{"id":38784,"date":"2022-09-14T18:42:00","date_gmt":"2022-09-15T01:42:00","guid":{"rendered":"https:\/\/blogv2prod.wpenginepowered.com\/blog\/?p=38784"},"modified":"2025-03-15T07:24:45","modified_gmt":"2025-03-15T14:24:45","slug":"what-are-the-common-signs-of-a-bad-thermostat","status":"publish","type":"post","link":"https:\/\/www.carparts.com\/blog\/what-are-the-common-signs-of-a-bad-thermostat\/","title":{"rendered":"What Are the Common Signs of a Bad Thermostat?"},"content":{"rendered":"<!DOCTYPE html PUBLIC \"-\/\/W3C\/\/DTD HTML 4.0 Transitional\/\/EN\" \"http:\/\/www.w3.org\/TR\/REC-html40\/loose.dtd\">\n<html><body><span class=\"span-reading-time rt-reading-time\" style=\"display: block;\"><span class=\"rt-label rt-prefix\">Reading Time: <\/span> <span class=\"rt-time\"> 6<\/span> <span class=\"rt-label rt-postfix\">minutes<\/span><\/span><style>.kadence-column38784_a4e286-63 > .kt-inside-inner-col,.kadence-column38784_a4e286-63 > .kt-inside-inner-col:before{border-top-left-radius:0px;border-top-right-radius:0px;border-bottom-right-radius:0px;border-bottom-left-radius:0px;}.kadence-column38784_a4e286-63 > .kt-inside-inner-col{column-gap:var(--global-kb-gap-sm, 1rem);}.kadence-column38784_a4e286-63 > .kt-inside-inner-col{flex-direction:column;}.kadence-column38784_a4e286-63 > .kt-inside-inner-col > .aligncenter{width:100%;}.kadence-column38784_a4e286-63 > .kt-inside-inner-col:before{opacity:0.3;}.kadence-column38784_a4e286-63{position:relative;}@media all and (max-width: 1024px){.kadence-column38784_a4e286-63 > .kt-inside-inner-col{flex-direction:column;justify-content:center;}}@media all and (max-width: 767px){.kadence-column38784_a4e286-63 > .kt-inside-inner-col{flex-direction:column;justify-content:center;}}<\/style>\n<div class=\"wp-block-kadence-column kadence-column38784_a4e286-63 inner-column-1 qk-look-widget\"><div class=\"kt-inside-inner-col\">\n<div class=\"wp-block-ultimate-post-row ultp-block-a68862  qk-main-wrap\"><div class=\"ultp-row-wrapper\"><div class=\"ultp-row-content\">\n<div class=\"wp-block-ultimate-post-column ultp-block-af1d1f\"><div class=\"ultp-column-wrapper\"><style>.wp-block-kadence-advancedheading.kt-adv-heading38784_be957d-4f, .wp-block-kadence-advancedheading.kt-adv-heading38784_be957d-4f[data-kb-block=\"kb-adv-heading38784_be957d-4f\"]{text-align:center;font-size:20px;font-style:normal;}.wp-block-kadence-advancedheading.kt-adv-heading38784_be957d-4f mark.kt-highlight, .wp-block-kadence-advancedheading.kt-adv-heading38784_be957d-4f[data-kb-block=\"kb-adv-heading38784_be957d-4f\"] mark.kt-highlight{font-family:Inter;font-weight:500;font-style:normal;color:#f76a0c;-webkit-box-decoration-break:clone;box-decoration-break:clone;padding-top:0px;padding-right:0px;padding-bottom:0px;padding-left:0px;}.wp-block-kadence-advancedheading.kt-adv-heading38784_be957d-4f img.kb-inline-image, .wp-block-kadence-advancedheading.kt-adv-heading38784_be957d-4f[data-kb-block=\"kb-adv-heading38784_be957d-4f\"] img.kb-inline-image{width:150px;vertical-align:baseline;}<\/style>\n<div class=\"kt-adv-heading38784_be957d-4f summary-title wp-block-kadence-advancedheading\" data-kb-block=\"kb-adv-heading38784_be957d-4f\"><span>Summary<\/span><\/div>\n\n\n\n<ul class=\"wp-block-list\">\n<li><strong>The thermostat is a valve that regulates coolant temperature, keeping it in the best range for the engine.<\/strong><\/li>\n\n\n\n<li>Although a stuck closed thermostat can cause overheating, modern thermostats more often fail by opening too soon or sticking open, which generally causes the engine to run too cool.<\/li>\n\n\n\n<li>You may be dealing with a faulty thermostat if your vehicle&rsquo;s temperature gauge reading is high into the red mark or running at the bottom end of the normal range.<\/li>\n\n\n\n<li>While driving without a thermostat almost never causes overheating, it does increase the risk of sludge formation due to the engine running too cold, and sludge in the oil pan can starve the engine for oil.<\/li>\n<\/ul>\n<\/div><\/div>\n<\/div><\/div><\/div>\n<\/div><\/div>\n\n\n\n\n\n<p>A healthy engine should run above 200 degrees. The radiator cooling fan on some vehicles doesn&rsquo;t even engage until after the coolant reaches nearly 230 degrees. Although most modern engines are expected to run 200-230&deg;F, most thermostats open at just under 200&deg;F.<\/p>\n\n\n\n<p>Disregarding a bad <a href=\"https:\/\/www.carparts.com\/thermostat\" target=\"_blank\" rel=\"noreferrer noopener\" aria-label=\"thermostat\">thermostat<\/a> may result in catastrophic engine failure, so you must replace it as soon as it begins to show signs of trouble. Fortunately, you can determine when it&rsquo;s time to get a replacement by watching for signs of a bad thermostat.<\/p>\n\n\n\n<h2 class=\"wp-block-heading\">What Does a Thermostat Do for Your Car?&nbsp;<\/h2>\n\n\n\n<p><strong>The thermostat is a valve that regulates coolant temperature and helps it stay at a certain preset level for optimal engine operation.<\/strong> It is located between the engine and the radiator.<\/p>\n\n\n\n<p>Although a stuck closed thermostat can cause overheating, modern thermostats more often fail by opening too soon or sticking open, which generally causes the engine to run too cool.<\/p>\n\n\n<style>.kadence-column38784_07a173-ac > .kt-inside-inner-col,.kadence-column38784_07a173-ac > .kt-inside-inner-col:before{border-top-left-radius:0px;border-top-right-radius:0px;border-bottom-right-radius:0px;border-bottom-left-radius:0px;}.kadence-column38784_07a173-ac > .kt-inside-inner-col{column-gap:var(--global-kb-gap-sm, 1rem);}.kadence-column38784_07a173-ac > .kt-inside-inner-col{flex-direction:column;}.kadence-column38784_07a173-ac > .kt-inside-inner-col > .aligncenter{width:100%;}.kadence-column38784_07a173-ac > .kt-inside-inner-col:before{opacity:0.3;}.kadence-column38784_07a173-ac{position:relative;}@media all and (max-width: 1024px){.kadence-column38784_07a173-ac > .kt-inside-inner-col{flex-direction:column;justify-content:center;}}@media all and (max-width: 767px){.kadence-column38784_07a173-ac > .kt-inside-inner-col{flex-direction:column;justify-content:center;}}<\/style>\n<div class=\"wp-block-kadence-column kadence-column38784_07a173-ac kb-section-dir-vertical kb-section-sm-dir-vertical inner-column-1 pro-tip-widget\"><div class=\"kt-inside-inner-col\"><style>.kb-row-layout-id38784_345e0a-a5 > .kt-row-column-wrap{align-content:start;}:where(.kb-row-layout-id38784_345e0a-a5 > .kt-row-column-wrap) > .wp-block-kadence-column{justify-content:start;}.kb-row-layout-id38784_345e0a-a5 > .kt-row-column-wrap{column-gap:var(--global-kb-gap-none, 0rem );row-gap:var(--global-kb-gap-md, 2rem);padding-top:20px;padding-right:32px;padding-bottom:20px;padding-left:16px;grid-template-columns:minmax(0, calc(10% - ((var(--global-kb-gap-none, 0rem ) * 1 )\/2)))minmax(0, calc(90% - ((var(--global-kb-gap-none, 0rem ) * 1 )\/2)));}.kb-row-layout-id38784_345e0a-a5 > .kt-row-layout-overlay{opacity:0.00;}.kb-row-layout-id38784_345e0a-a5 .kt-row-layout-bottom-sep{height:100px;}.kb-row-layout-id38784_345e0a-a5 .kt-row-layout-bottom-sep svg{width:100%;}.kb-row-layout-id38784_345e0a-a5 .kt-row-layout-bottom-sep svg{fill:#ffffff!important;}.kb-row-layout-id38784_345e0a-a5 .kt-row-layout-top-sep{height:100px;}.kb-row-layout-id38784_345e0a-a5 .kt-row-layout-top-sep svg{width:100%;}.kb-row-layout-id38784_345e0a-a5 .kt-row-layout-top-sep svg{fill:#ffffff!important;}@media all and (max-width: 1024px){.kb-row-layout-id38784_345e0a-a5 > .kt-row-column-wrap{grid-template-columns:minmax(0, 1fr) minmax(0, 2fr);}}@media all and (max-width: 1024px){.kb-row-layout-id38784_345e0a-a5 .kt-row-layout-bottom-sep{height:px;}}@media all and (max-width: 1024px){.kb-row-layout-id38784_345e0a-a5 .kt-row-layout-bottom-sep svg{width:%;}}@media all and (max-width: 767px){.kb-row-layout-id38784_345e0a-a5 > .kt-row-column-wrap{padding-top:28px;padding-right:16px;padding-bottom:25px;padding-left:16px;grid-template-columns:minmax(0, 1fr) minmax(0, 2fr);}.kb-row-layout-id38784_345e0a-a5 .kt-row-layout-bottom-sep{height:px;}.kb-row-layout-id38784_345e0a-a5 .kt-row-layout-bottom-sep svg{width:%;}}<\/style><div class=\"kb-row-layout-wrap kb-row-layout-id38784_345e0a-a5 alignnone pro-tip-wrap wp-block-kadence-rowlayout\"><div class=\"kt-row-column-wrap kt-has-2-columns kt-row-layout-right-golden kt-tab-layout-right-golden kt-mobile-layout-right-golden kt-row-valign-top\">\n<style>.kadence-column38784_02d32a-f6 > .kt-inside-inner-col{display:flex;}.kadence-column38784_02d32a-f6 > .kt-inside-inner-col{min-height:45px;}.kadence-column38784_02d32a-f6 > .kt-inside-inner-col,.kadence-column38784_02d32a-f6 > .kt-inside-inner-col:before{border-top-left-radius:0px;border-top-right-radius:0px;border-bottom-right-radius:0px;border-bottom-left-radius:0px;}.kadence-column38784_02d32a-f6 > .kt-inside-inner-col{row-gap:0px;column-gap:0px;}.kadence-column38784_02d32a-f6 > .kt-inside-inner-col{flex-direction:row;flex-wrap:wrap;align-items:center;}.kadence-column38784_02d32a-f6 > .kt-inside-inner-col > *, .kadence-column38784_02d32a-f6 > .kt-inside-inner-col > figure.wp-block-image, .kadence-column38784_02d32a-f6 > .kt-inside-inner-col > figure.wp-block-kadence-image{margin-top:0px;margin-bottom:0px;}.kadence-column38784_02d32a-f6 > .kt-inside-inner-col > .kb-image-is-ratio-size{flex-grow:1;}.kadence-column38784_02d32a-f6 > .kt-inside-inner-col:before{opacity:0.3;}.kadence-column38784_02d32a-f6{position:relative;}@media all and (max-width: 1024px){.kadence-column38784_02d32a-f6 > .kt-inside-inner-col{flex-direction:row;flex-wrap:wrap;align-items:center;}}@media all and (min-width: 768px) and (max-width: 1024px){.kadence-column38784_02d32a-f6 > .kt-inside-inner-col > *, .kadence-column38784_02d32a-f6 > .kt-inside-inner-col > figure.wp-block-image, .kadence-column38784_02d32a-f6 > .kt-inside-inner-col > figure.wp-block-kadence-image{margin-top:0px;margin-bottom:0px;}.kadence-column38784_02d32a-f6 > .kt-inside-inner-col > .kb-image-is-ratio-size{flex-grow:1;}}@media all and (max-width: 767px){.kadence-column38784_02d32a-f6 > .kt-inside-inner-col{flex-direction:row;flex-wrap:wrap;justify-content:flex-start;}.kadence-column38784_02d32a-f6 > .kt-inside-inner-col > *, .kadence-column38784_02d32a-f6 > .kt-inside-inner-col > figure.wp-block-image, .kadence-column38784_02d32a-f6 > .kt-inside-inner-col > figure.wp-block-kadence-image{margin-top:0px;margin-bottom:0px;}.kadence-column38784_02d32a-f6 > .kt-inside-inner-col > .kb-image-is-ratio-size{flex-grow:1;}}<\/style>\n<div class=\"wp-block-kadence-column kadence-column38784_02d32a-f6 kb-section-dir-horizontal kb-section-md-dir-horizontal inner-column-1 pro-tip-item1\"><div class=\"kt-inside-inner-col\"><style>.kb-image38784_4890c6-3a.kb-image-is-ratio-size, .kb-image38784_4890c6-3a .kb-image-is-ratio-size{max-width:45px;width:100%;}.wp-block-kadence-column > .kt-inside-inner-col > .kb-image38784_4890c6-3a.kb-image-is-ratio-size, .wp-block-kadence-column > .kt-inside-inner-col > .kb-image38784_4890c6-3a .kb-image-is-ratio-size{align-self:unset;}.kb-image38784_4890c6-3a figure{max-width:45px;}.kb-image38784_4890c6-3a .image-is-svg, .kb-image38784_4890c6-3a .image-is-svg img{width:100%;}.kb-image38784_4890c6-3a .kb-image-has-overlay:after{opacity:0.3;}<\/style>\n<div class=\"wp-block-kadence-image kb-image38784_4890c6-3a\"><figure class=\"aligncenter size-large\"><img decoding=\"async\" src=\"https:\/\/cld.partsimg.com\/image\/upload\/f_auto,dpr_auto,q_auto,c_pad\/carparts\/blog\/widgets\/protip\/services-icon\" alt=\"\" class=\"kb-img\"><\/figure><\/div>\n<\/div><\/div>\n\n\n<style>.kadence-column38784_4e2bcf-7a > .kt-inside-inner-col,.kadence-column38784_4e2bcf-7a > .kt-inside-inner-col:before{border-top-left-radius:0px;border-top-right-radius:0px;border-bottom-right-radius:0px;border-bottom-left-radius:0px;}.kadence-column38784_4e2bcf-7a > .kt-inside-inner-col{column-gap:var(--global-kb-gap-sm, 1rem);}.kadence-column38784_4e2bcf-7a > .kt-inside-inner-col{flex-direction:column;}.kadence-column38784_4e2bcf-7a > .kt-inside-inner-col > .aligncenter{width:100%;}.kadence-column38784_4e2bcf-7a > .kt-inside-inner-col:before{opacity:0.3;}.kadence-column38784_4e2bcf-7a{position:relative;}@media all and (max-width: 1024px){.kadence-column38784_4e2bcf-7a > .kt-inside-inner-col{flex-direction:column;justify-content:center;}}@media all and (max-width: 767px){.kadence-column38784_4e2bcf-7a > .kt-inside-inner-col{flex-direction:column;justify-content:center;}}<\/style>\n<div class=\"wp-block-kadence-column kadence-column38784_4e2bcf-7a inner-column-2 pro-tip-item2\"><div class=\"kt-inside-inner-col\">\n<div class=\"protip-desc\">\n\t<div class=\"help-tip\">\n\t\t<p><strong>Pro Tips<\/strong> are nuggets of information direct from ASE-certified automobile technicians working with CarParts.com, which may include unique, personal insights based on their years of experience working in the automotive industry. These can help you make more informed decisions about your car.<\/p>\n\t<\/div>\n    <div class=\"help-caption\">\n        <p>\n            <strong>Pro Tip:<\/strong>\n            If, in the winter, you notice your engine running cooler than expected and you don&rsquo;t have good cabin heat, the thermostat is most likely at the root of the problem. Emissions and fuel economy are also negatively impacted by a cold-running engine.\n        <\/p>\n    <\/div>\n<\/div>\n<\/div><\/div>\n\n<\/div><\/div><\/div><\/div>\n\n\n\n<div class=\"wp-block-data443-irp-shortcode irp-shortcode\"><div style=\"clear:both; margin-top:0em; margin-bottom:1em;\"><a href=\"https:\/\/www.carparts.com\/blog\/p0597-code-thermostat-heater-control-circuit-open\/\" target=\"_self\" rel=\"dofollow\" class=\"u2884fe32f6a3f940f41edb98f66a1fc5\"><style> .u2884fe32f6a3f940f41edb98f66a1fc5 { padding:0px; margin: 0; padding-top:1em!important; padding-bottom:1em!important; width:100%; display: block; font-weight:bold; background-color:#eaeaea; border:0!important; border-left:4px solid #34495E!important; text-decoration:none; } .u2884fe32f6a3f940f41edb98f66a1fc5:active, .u2884fe32f6a3f940f41edb98f66a1fc5:hover { opacity: 1; transition: opacity 250ms; webkit-transition: opacity 250ms; text-decoration:none; } .u2884fe32f6a3f940f41edb98f66a1fc5 { transition: background-color 250ms; webkit-transition: background-color 250ms; opacity: 1; transition: opacity 250ms; webkit-transition: opacity 250ms; } .u2884fe32f6a3f940f41edb98f66a1fc5 .ctaText { font-weight:bold; color:#464646; text-decoration:none; font-size: 16px; } .u2884fe32f6a3f940f41edb98f66a1fc5 .postTitle { color:#000000; text-decoration: underline!important; font-size: 16px; } .u2884fe32f6a3f940f41edb98f66a1fc5:hover .postTitle { text-decoration: underline!important; } <\/style><div style=\"padding-left:1em; padding-right:1em;\"><span class=\"ctaText\">See also<\/span>&nbsp; <span class=\"postTitle\">P0597 Code: Thermostat Heater Control Circuit \/ Open<\/span><\/div><\/a><\/div><\/div>\n\n\n\n<p>But other than the obvious impact a cold running engine can have on emissions and fuel economy, an engine that runs too cold for too long can begin to develop crankcase sludge even if the oil is changed regularly.<\/p>\n\n\n\n<figure class=\"wp-block-image size-large is-resized\"><img loading=\"lazy\" decoding=\"async\" width=\"1024\" height=\"683\" src=\"https:\/\/www.carparts.com\/blog\/wp-content\/uploads\/2021\/05\/New-car-thermostat-isolated-on-white-1024x683.jpg\" alt=\"New car thermostat isolated in white\" class=\"wp-image-38805\" style=\"width:1024px;height:683px\" srcset=\"https:\/\/www.carparts.com\/blog\/wp-content\/uploads\/2021\/05\/New-car-thermostat-isolated-on-white-1024x683.jpg 1024w, https:\/\/www.carparts.com\/blog\/wp-content\/uploads\/2021\/05\/New-car-thermostat-isolated-on-white-300x200.jpg 300w, https:\/\/www.carparts.com\/blog\/wp-content\/uploads\/2021\/05\/New-car-thermostat-isolated-on-white-768x512.jpg 768w, https:\/\/www.carparts.com\/blog\/wp-content\/uploads\/2021\/05\/New-car-thermostat-isolated-on-white-600x400.jpg 600w, https:\/\/www.carparts.com\/blog\/wp-content\/uploads\/2021\/05\/New-car-thermostat-isolated-on-white-150x100.jpg 150w, https:\/\/www.carparts.com\/blog\/wp-content\/uploads\/2021\/05\/New-car-thermostat-isolated-on-white.jpg 1500w\" sizes=\"(max-width: 1024px) 100vw, 1024px\"><figcaption class=\"wp-element-caption\">The thermostat is a valve that regulates coolant temperature and helps it stay at a certain preset level for optimal engine operation.<\/figcaption><\/figure>\n\n\n\n<h2 class=\"wp-block-heading\">How Does a Thermostat Work?&nbsp;<\/h2>\n\n\n\n<p>You may be wondering, &ldquo;What does a car thermostat even do?&rdquo; Most thermostats have a wax-filled brass tube that expands as the coolant gets hot, opening the thermostat&rsquo;s valve against spring pressure. A thermostat&rsquo;s temperature rating represents the point at which the thermostat starts to open.<\/p>\n\n\n\n<p>While the thermostat is closed, the coolant is pumped through the heater core or through a heater core bypass valve that only opens when cabin heat is requested.<\/p>\n\n\n\n<p>When coolant temperature expands the wax pellet to open the valve, the coolant flows through the <a href=\"https:\/\/www.carparts.com\/radiator\" target=\"_blank\" rel=\"noreferrer noopener\" aria-label=\"radiator\">radiator<\/a> to carry engine heat away so that the coolant returning to the engine is cool, and the thermostat closes again until the coolant gets hot enough to open it again. You can actually watch this thermostat cycling happen if you graph the <a href=\"https:\/\/www.carparts.com\/blog\/engine-coolant-temperature-sensor-purpose-location-and-failure-signs\/\" target=\"_blank\" rel=\"noreferrer noopener\" aria-label=\"engine coolant temperature sensor\">engine coolant temperature sensor<\/a> on an idling engine.<\/p>\n\n\n\n<figure class=\"wp-block-image size-large is-resized\"><img loading=\"lazy\" decoding=\"async\" width=\"974\" height=\"1024\" src=\"https:\/\/www.carparts.com\/blog\/wp-content\/uploads\/2022\/09\/conventional-thermostat-974x1024.jpg\" alt=\"conventional thermostat\" class=\"wp-image-73803\" style=\"width:974px;height:1024px\" srcset=\"https:\/\/www.carparts.com\/blog\/wp-content\/uploads\/2022\/09\/conventional-thermostat-974x1024.jpg 974w, https:\/\/www.carparts.com\/blog\/wp-content\/uploads\/2022\/09\/conventional-thermostat-285x300.jpg 285w, https:\/\/www.carparts.com\/blog\/wp-content\/uploads\/2022\/09\/conventional-thermostat-768x807.jpg 768w, https:\/\/www.carparts.com\/blog\/wp-content\/uploads\/2022\/09\/conventional-thermostat-150x158.jpg 150w, https:\/\/www.carparts.com\/blog\/wp-content\/uploads\/2022\/09\/conventional-thermostat.jpg 1427w\" sizes=\"(max-width: 974px) 100vw, 974px\"><figcaption class=\"wp-element-caption\">A conventional thermostat that was stuck open and was causing the engine to run too cool | Image Source: Richard McCuistian<\/figcaption><\/figure>\n\n\n\n<figure class=\"wp-block-image size-large is-resized\"><img loading=\"lazy\" decoding=\"async\" width=\"1024\" height=\"765\" src=\"https:\/\/www.carparts.com\/blog\/wp-content\/uploads\/2022\/09\/2020-toyota-corolla-thermostat-1024x765.jpg\" alt=\"2020 toyota corolla thermostat\" class=\"wp-image-73804\" style=\"width:1024px;height:765px\" srcset=\"https:\/\/www.carparts.com\/blog\/wp-content\/uploads\/2022\/09\/2020-toyota-corolla-thermostat-1024x765.jpg 1024w, https:\/\/www.carparts.com\/blog\/wp-content\/uploads\/2022\/09\/2020-toyota-corolla-thermostat-300x224.jpg 300w, https:\/\/www.carparts.com\/blog\/wp-content\/uploads\/2022\/09\/2020-toyota-corolla-thermostat-768x574.jpg 768w, https:\/\/www.carparts.com\/blog\/wp-content\/uploads\/2022\/09\/2020-toyota-corolla-thermostat-150x112.jpg 150w, https:\/\/www.carparts.com\/blog\/wp-content\/uploads\/2022\/09\/2020-toyota-corolla-thermostat.jpg 1500w\" sizes=\"(max-width: 1024px) 100vw, 1024px\"><figcaption class=\"wp-element-caption\">Some newer engines have a heating element so that the ECM\/PCM can heat the wax element electrically and control the opening of the thermostat. One example of this kind of thermostat is found on some 2020 Toyota Corollas, such as the one in this photo. The thermostat is part of the housing. This thermostat was also replaced due to a cold-running engine and a stored P0128 code. | Image Source: Richard McCuistian<\/figcaption><\/figure>\n\n\n\n<p>The temperature at which the valve begins to open depends on the vehicle. Most late model thermostats open once the engine reaches 195 to 200 F. Once the engine shuts off and cools down, the wax contracts and closes the thermostat.<\/p>\n\n\n\n<h2 class=\"wp-block-heading\">What Are the Possible Signs of a Bad Thermostat?<\/h2>\n\n\n\n<p>When your vehicle&rsquo;s engine temperatures are reaching abnormal ranges, you can look out&nbsp; for a number of symptoms of a stuck open or closed thermostat. Here&rsquo;s how to know your thermostat is bad:<\/p>\n\n\n\n<h3 class=\"wp-block-heading\">Engine Running Too Cool or Too Hot<\/h3>\n\n\n\n<p>You may be dealing with a faulty thermostat if your vehicle&rsquo;s <a href=\"https:\/\/www.carparts.com\/temperature-gauge\" target=\"_blank\" rel=\"noreferrer noopener\" aria-label=\"temperature gauge\">temperature gauge<\/a> reading is high into the red mark or running at the bottom end of the normal range. An engine that is running too cool will store a <a href=\"https:\/\/www.carparts.com\/blog\/p0125-code-insufficient-coolant-temperature-for-closed-loop-fuel-control\/\" target=\"_blank\" rel=\"noreferrer noopener\" aria-label=\"P0125\">P0125<\/a> or a <a href=\"https:\/\/www.carparts.com\/blog\/p0128-coolant-temperature-below-thermostat-regulating-temperature\/\" target=\"_blank\" rel=\"noreferrer noopener\" aria-label=\"P0128 code\">P0128 code<\/a>.<\/p>\n\n\n\n<div class=\"wp-block-data443-irp-shortcode irp-shortcode\"><div style=\"clear:both; margin-top:0em; margin-bottom:1em;\"><a href=\"https:\/\/www.carparts.com\/blog\/what-type-of-damage-to-expect-from-an-overheating-car\/\" target=\"_self\" rel=\"dofollow\" class=\"u5213f5f317e92d1db2162cbbd562020e\"><style> .u5213f5f317e92d1db2162cbbd562020e { padding:0px; margin: 0; padding-top:1em!important; padding-bottom:1em!important; width:100%; display: block; font-weight:bold; background-color:#eaeaea; border:0!important; border-left:4px solid #34495E!important; text-decoration:none; } .u5213f5f317e92d1db2162cbbd562020e:active, .u5213f5f317e92d1db2162cbbd562020e:hover { opacity: 1; transition: opacity 250ms; webkit-transition: opacity 250ms; text-decoration:none; } .u5213f5f317e92d1db2162cbbd562020e { transition: background-color 250ms; webkit-transition: background-color 250ms; opacity: 1; transition: opacity 250ms; webkit-transition: opacity 250ms; } .u5213f5f317e92d1db2162cbbd562020e .ctaText { font-weight:bold; color:#464646; text-decoration:none; font-size: 16px; } .u5213f5f317e92d1db2162cbbd562020e .postTitle { color:#000000; text-decoration: underline!important; font-size: 16px; } .u5213f5f317e92d1db2162cbbd562020e:hover .postTitle { text-decoration: underline!important; } <\/style><div style=\"padding-left:1em; padding-right:1em;\"><span class=\"ctaText\">See also<\/span>&nbsp; <span class=\"postTitle\">What Type of Damage to Expect From an Overheating Car<\/span><\/div><\/a><\/div><\/div>\n\n\n\n<p>This could mean that the thermostat is stuck closed if the engine is running too hot or opening too soon if the engine is running too cold. And while an <a href=\"https:\/\/www.carparts.com\/blog\/coolant-temperature-warning-light-meaning-causes-what-to-do\/\" target=\"_blank\" rel=\"noreferrer noopener\" aria-label=\"overheating engine\">overheating engine<\/a> may also be caused by other parts, such as a busted or clogged radiator, a defective cooling fan, or a weak water pump, a thermostat is usually a good cheap first step, unless it&rsquo;s extremely difficult to access (and on some engines that&rsquo;s the case). To be sure, it&rsquo;s best to have your vehicle checked by a certified mechanic for a proper diagnosis.<\/p>\n\n\n\n<h3 class=\"wp-block-heading\">Illuminated Check Engine Light<\/h3>\n\n\n\n<p>A broken thermostat may also illuminate the check engine light. Check if the thermostat is stuck open\/closed or if it doesn&rsquo;t respond to temperature conditions. Fixing the position or replacing the damaged thermostat should clear the check engine light.<\/p>\n\n\n\n<div id=\"article-search-widget\">\n<div class=\"cp-search\">\n<div align=\"center\">\n<img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/cld.partsimg.com\/image\/upload\/w_auto,dpr_auto\/carparts\/logos\/badge_wordmark\/full_color\/CP_LOGO_COLOUR_RGB\" alt=\"CarParts.com\" width=\"300\" height=\"56\">\n<\/div>\n<form id=\"cpsearchform\" name=\"cpsearchform\" action=\"https:\/\/www.carparts.com\/search\" method=\"get\" target=\"_blank\" accept-charset=\"character_set\" aria-label=\"search CarParts.com\">\n    <input type=\"text\" class=\"keyword\" name=\"q\" placeholder=\"Search for parts on CarParts.com\" value=\"\" aria-label=\"Search CarParts.com\"><input type=\"submit\" class=\"btn-search\" value=\"Search\" aria-label=\"Search\">\n<\/form>\n<\/div>\n<\/div>\n\n\n\n<h2 class=\"wp-block-heading\">Effects of a Bad Thermostat<\/h2>\n\n\n\n<p>A thermostat can fail in either the open or closed position. When the thermostat stays closed, the engine will begin to overheat, potentially leading to extensive engine and cooling system damage. Because of this, we don&rsquo;t recommend driving with your thermostat stuck closed.<\/p>\n\n\n\n<p>On the other hand, if the thermostat is stuck open, the engine will fail to reach operating temperature, resulting in issues, such as an inoperative cabin heater, increased fuel consumption, and possible engine wear.<\/p>\n\n\n\n<h2 class=\"wp-block-heading\">How to Diagnose a Faulty Thermostat<\/h2>\n\n\n\n<p>To check if your vehicle has a defective thermostat that is stuck closed, feel the upper <a href=\"https:\/\/www.carparts.com\/radiator-hose\" target=\"_blank\" rel=\"noreferrer noopener\" aria-label=\"radiator hose\">radiator hose<\/a> after the engine has had time to warm up. A cool radiator hose usually means the thermostat is stuck closed, restricting coolant from flowing from the engine to the radiator.<\/p>\n\n\n\n<p>Note that a cool <a href=\"https:\/\/www.carparts.com\/blog\/radiator-hose-problems-6-symptoms-of-a-bad-or-failing-radiator-hose\/\" target=\"_blank\" rel=\"noreferrer noopener\" aria-label=\"radiator hose\">radiator hose<\/a> could also mean that the engine has a low coolant level, trapped air bubbles under the thermostat, or a bad water pump. One test often performed is to remove the thermostat from the engine and drop it into a bucket of boiling water (over 200 degrees). The thermostat should open while it&rsquo;s submerged close once it&rsquo;s pulled out. If it fails this test, the thermostat is defective and should be replaced immediately.<\/p>\n\n\n\n<p>That being said, sometimes a thermostat will pass this test and still be defective, so this isn&rsquo;t a go-no-go in every case. It&rsquo;s best to go ahead and replace the thermostat unless it&rsquo;s configured differently. Some thermostats are built into the housing (like on a mid-2000s <a href=\"https:\/\/www.carparts.com\/blog\/chevrolet-blazer-reliability-and-common-problems\/\" target=\"_blank\" rel=\"noreferrer noopener\" aria-label=\"Chevy Trailblazer\">Chevy Trailblazer<\/a>) and those are a bit more difficult to test definitively.<\/p>\n\n\n\n<div class=\"wp-block-data443-irp-shortcode irp-shortcode\"><div style=\"clear:both; margin-top:0em; margin-bottom:1em;\"><a href=\"https:\/\/www.carparts.com\/blog\/p0125-code-insufficient-coolant-temperature-for-closed-loop-fuel-control\/\" target=\"_self\" rel=\"dofollow\" class=\"uabc4d9d95c5ea8dc3bb9a9e3e4d32894\"><style> .uabc4d9d95c5ea8dc3bb9a9e3e4d32894 { padding:0px; margin: 0; padding-top:1em!important; padding-bottom:1em!important; width:100%; display: block; font-weight:bold; background-color:#eaeaea; border:0!important; border-left:4px solid #34495E!important; text-decoration:none; } .uabc4d9d95c5ea8dc3bb9a9e3e4d32894:active, .uabc4d9d95c5ea8dc3bb9a9e3e4d32894:hover { opacity: 1; transition: opacity 250ms; webkit-transition: opacity 250ms; text-decoration:none; } .uabc4d9d95c5ea8dc3bb9a9e3e4d32894 { transition: background-color 250ms; webkit-transition: background-color 250ms; opacity: 1; transition: opacity 250ms; webkit-transition: opacity 250ms; } .uabc4d9d95c5ea8dc3bb9a9e3e4d32894 .ctaText { font-weight:bold; color:#464646; text-decoration:none; font-size: 16px; } .uabc4d9d95c5ea8dc3bb9a9e3e4d32894 .postTitle { color:#000000; text-decoration: underline!important; font-size: 16px; } .uabc4d9d95c5ea8dc3bb9a9e3e4d32894:hover .postTitle { text-decoration: underline!important; } <\/style><div style=\"padding-left:1em; padding-right:1em;\"><span class=\"ctaText\">See also<\/span>&nbsp; <span class=\"postTitle\">P0125 Code: Insufficient Coolant Temperature for Closed Loop Fuel Control<\/span><\/div><\/a><\/div><\/div>\n\n\n\n<p>If the thermostat is stuck open, the heater might not produce enough warmth during cold weather and the engine may take more time to reach its normal operating temperature. These issues are usually caused by a defective wax element or broken return spring.<\/p>\n\n\n\n<h2 class=\"wp-block-heading\">Why Should You Replace a Bad Thermostat?&nbsp;<\/h2>\n\n\n\n<p>Aside from maintaining the engine&rsquo;s optimal performance, getting a new thermostat reduces the risk of <a href=\"https:\/\/www.carparts.com\/blog\/what-damage-to-expect-from-an-overheating-car\/\" target=\"_blank\" rel=\"noreferrer noopener\" aria-label=\"overheating\">overheating<\/a> and thermostat failure. Experts recommend changing the thermostat every ten years for preventive maintenance, especially on early-model and high-mileage vehicles.<\/p>\n\n\n\n<h2 class=\"wp-block-heading\">Can You Drive Without a Thermostat?<\/h2>\n\n\n\n<p>It is not advisable to run your engine without a thermostat. While driving without a thermostat almost never causes overheating, it does increase the risk of sludge formation due to the engine running too cold, and sludge in the oil pan can starve the engine for oil.<\/p>\n\n\n\n<h2 class=\"wp-block-heading\">Replacing a Bad Thermostat&nbsp;<\/h2>\n\n\n\n<p>A new thermostat can cost anywhere between $10 and $600 (for just the part), depending on your vehicle&rsquo;s year, make and model. Other factors that may affect the price include the thermostat&rsquo;s open temperature rating, material, and brand. To make sure you&rsquo;re getting the right thermostat for your vehicle, select a product that&rsquo;s designed to fit your application. You&rsquo;ll also want to select a thermostat that&rsquo;s designed to open at the same temperature as your original thermostat.<\/p>\n\n\n\n<p>Replacing a bad thermostat is considered a DIY-friendly repair job on most vehicles, as it only involves a few tools, and the procedure is pretty straightforward. However, if you&rsquo;re not confident with your DIY skills or you don&rsquo;t know how to properly fill the engine with coolant (which can be more complicated than it would seem), it may be best to have a professional do it.<\/p>\n<\/body><\/html>\n","protected":false},"excerpt":{"rendered":"<p><span class=\"span-reading-time rt-reading-time\" style=\"display: block;\"><span class=\"rt-label rt-prefix\">Reading Time: <\/span> <span class=\"rt-time\"> 6<\/span> <span class=\"rt-label rt-postfix\">minutes<\/span><\/span>A healthy engine should run above 200 degrees. The radiator cooling fan on some vehicles doesn&rsquo;t even engage until after&#8230; <a href=\"https:\/\/www.carparts.com\/blog\/what-are-the-common-signs-of-a-bad-thermostat\/\" rel=\"nofollow\">Read More<\/a><\/p>\n","protected":false},"author":4,"featured_media":38811,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"_acf_changed":false,"_genesis_hide_title":false,"_genesis_hide_breadcrumbs":false,"_genesis_hide_singular_image":false,"_genesis_hide_footer_widgets":false,"_genesis_custom_body_class":"","_genesis_custom_post_class":"","_genesis_layout":"","footnotes":""},"categories":[3753,52],"tags":[1214,332],"ppma_author":[2607,2985],"class_list":{"0":"post-38784","1":"post","2":"type-post","3":"status-publish","4":"format-standard","5":"has-post-thumbnail","7":"category-cooling-system","8":"category-diy","9":"tag-temperature-gauge","10":"tag-thermostat","11":"entry"},"acf":{"adrotate_specific_mobile_ad":"","adrotate_specific_desktop_ad":""},"yoast_head":"<!-- This site is optimized with the Yoast SEO plugin v27.7 - https:\/\/yoast.com\/product\/yoast-seo-wordpress\/ -->\n<title>What Are the Common Signs of a Bad Thermostat? - In The Garage with CarParts.com<\/title>\n<meta name=\"description\" content=\"Learn more about the signs of a bad thermostat and why you should replace it as soon as possible. Plus check how much a replacement costs.\" \/>\n<meta name=\"robots\" content=\"index, follow, max-snippet:-1, max-image-preview:large, max-video-preview:-1\" \/>\n<link rel=\"canonical\" href=\"https:\/\/www.carparts.com\/blog\/what-are-the-common-signs-of-a-bad-thermostat\/\" \/>\n<meta property=\"og:locale\" content=\"en_US\" \/>\n<meta property=\"og:type\" content=\"article\" \/>\n<meta property=\"og:title\" content=\"What Are the Common Signs of a Bad Thermostat? - In The Garage with CarParts.com\" \/>\n<meta property=\"og:description\" content=\"Learn more about the signs of a bad thermostat and why you should replace it as soon as possible. Plus check how much a replacement costs.\" \/>\n<meta property=\"og:url\" content=\"https:\/\/www.carparts.com\/blog\/what-are-the-common-signs-of-a-bad-thermostat\/\" \/>\n<meta property=\"og:site_name\" content=\"In The Garage with CarParts.com\" \/>\n<meta property=\"article:publisher\" content=\"https:\/\/www.facebook.com\/carpartscom\" \/>\n<meta property=\"article:published_time\" content=\"2022-09-15T01:42:00+00:00\" \/>\n<meta property=\"article:modified_time\" content=\"2025-03-15T14:24:45+00:00\" \/>\n<meta property=\"og:image\" content=\"https:\/\/www.carparts.com\/blog\/wp-content\/uploads\/2021\/05\/car-thermostat-inspection.jpg\" \/>\n\t<meta property=\"og:image:width\" content=\"1500\" \/>\n\t<meta property=\"og:image:height\" content=\"1000\" \/>\n\t<meta property=\"og:image:type\" content=\"image\/jpeg\" \/>\n<meta name=\"twitter:card\" content=\"summary_large_image\" \/>\n<meta name=\"twitter:creator\" content=\"@carpartscom\" \/>\n<meta name=\"twitter:site\" content=\"@carpartscom\" \/>\n<meta name=\"twitter:label1\" content=\"Written by\" \/>\n\t<meta name=\"twitter:data1\" content=\"\" \/>\n\t<meta name=\"twitter:label2\" content=\"Est. reading time\" \/>\n\t<meta name=\"twitter:data2\" content=\"7 minutes\" \/>\n<script type=\"application\/ld+json\" class=\"yoast-schema-graph\">{\"@context\":\"https:\\\/\\\/schema.org\",\"@graph\":[{\"@type\":\"Article\",\"@id\":\"https:\\\/\\\/www.carparts.com\\\/blog\\\/what-are-the-common-signs-of-a-bad-thermostat\\\/#article\",\"isPartOf\":{\"@id\":\"https:\\\/\\\/www.carparts.com\\\/blog\\\/what-are-the-common-signs-of-a-bad-thermostat\\\/\"},\"author\":[{\"@type\":\"Person\",\"$id\":\"4\",\"name\":\"CarParts.com Research Team\",\"jobTitle\":\"Expert Automotive Writer\",\"description\":\"The CarParts.com Research Team is composed of experienced automotive and tech writers working with (ASE)-certified automobile technicians and automotive journalists to bring up-to-date, helpful information to car owners in the US. 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