{"id":108016,"date":"2024-06-06T05:36:34","date_gmt":"2024-06-06T12:36:34","guid":{"rendered":"https:\/\/blogv2prod.wpenginepowered.com\/blog\/?p=108016"},"modified":"2025-10-23T21:17:10","modified_gmt":"2025-10-24T04:17:10","slug":"overfilled-coolant-reservoir-consequences-causes-and-solutions","status":"publish","type":"post","link":"https:\/\/www.carparts.com\/blog\/overfilled-coolant-reservoir-consequences-causes-and-solutions\/","title":{"rendered":"Overfilled Coolant Reservoir: Consequences, Causes, and Solutions"},"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\"> 3<\/span> <span class=\"rt-label rt-postfix\">minutes<\/span><\/span><style>.kadence-column108016_e5b8eb-bf > .kt-inside-inner-col,.kadence-column108016_e5b8eb-bf > .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-column108016_e5b8eb-bf > .kt-inside-inner-col{column-gap:var(--global-kb-gap-sm, 1rem);}.kadence-column108016_e5b8eb-bf > .kt-inside-inner-col{flex-direction:column;}.kadence-column108016_e5b8eb-bf > .kt-inside-inner-col > .aligncenter{width:100%;}.kadence-column108016_e5b8eb-bf > .kt-inside-inner-col:before{opacity:0.3;}.kadence-column108016_e5b8eb-bf{position:relative;}@media all and (max-width: 1024px){.kadence-column108016_e5b8eb-bf > .kt-inside-inner-col{flex-direction:column;justify-content:center;}}@media all and (max-width: 767px){.kadence-column108016_e5b8eb-bf > .kt-inside-inner-col{flex-direction:column;justify-content:center;}}<\/style>\n<div class=\"wp-block-kadence-column kadence-column108016_e5b8eb-bf inner-column-1 qk-look-widget\"><div class=\"kt-inside-inner-col\">\n<div class=\"wp-block-ultimate-post-row ultp-block-0bd113  qk-main-wrap\"><div class=\"ultp-row-wrapper\"><div class=\"ultp-row-content\">\n<div class=\"wp-block-ultimate-post-column ultp-block-d6404b\"><div class=\"ultp-column-wrapper\"><style>.wp-block-kadence-advancedheading.kt-adv-heading108016_e7caef-5c, .wp-block-kadence-advancedheading.kt-adv-heading108016_e7caef-5c[data-kb-block=\"kb-adv-heading108016_e7caef-5c\"]{text-align:center;font-size:20px;font-style:normal;}.wp-block-kadence-advancedheading.kt-adv-heading108016_e7caef-5c mark.kt-highlight, .wp-block-kadence-advancedheading.kt-adv-heading108016_e7caef-5c[data-kb-block=\"kb-adv-heading108016_e7caef-5c\"] 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-heading108016_e7caef-5c img.kb-inline-image, .wp-block-kadence-advancedheading.kt-adv-heading108016_e7caef-5c[data-kb-block=\"kb-adv-heading108016_e7caef-5c\"] img.kb-inline-image{width:150px;vertical-align:baseline;}<\/style>\n<div class=\"kt-adv-heading108016_e7caef-5c summary-title wp-block-kadence-advancedheading\" data-kb-block=\"kb-adv-heading108016_e7caef-5c\"><span>Summary<\/span><\/div>\n\n\n\n<ul class=\"wp-block-list\">\n<li>You shouldn&rsquo;t overfill your coolant reservoir. Doing so will cause the cooling system to push the coolant out of the pressure cap.<\/li>\n\n\n\n<li>Often, an overflowing coolant reservoir is the result of human error. You might have simply overfilled your coolant reservoir and will need to drain it through the drain plug on the bottom of the radiator. Remember to use proper procedure when draining coolant.<\/li>\n\n\n\n<li>Other common causes for overflowing coolant include a worn radiator cap, a faulty thermostat, and a blocked radiator.<\/li>\n<\/ul>\n<\/div><\/div>\n<\/div><\/div><\/div>\n<\/div><\/div>\n\n\n\n\n\n<p>Overfilling the coolant reservoir will cause the cooling system to push the coolant out of the pressure cap.<\/p>\n\n\n\n<p>Often, an overflowing coolant reservoir is the result of human error. You might have simply overfilled your coolant reservoir and will need to drain it through the drain plug on the bottom of the radiator. Remember to use proper procedure when draining coolant.<\/p>\n\n\n\n<p>But there may be other reasons for an overfilled coolant reservoir. Let&rsquo;s take a closer look.<\/p>\n\n\n\n<h2 class=\"wp-block-heading\">Overfilled Coolant Reservoir Causes and Solutions<\/h2>\n\n\n\n<p>Tracking down the main cause behind your overflowing coolant might take some investigating. In this section, we&rsquo;ll be going over some of the most common causes and their possible fixes. Bring your vehicle to a trusted mechanic if you can&rsquo;t figure out the main problem though. They can investigate your overflowing coolant further.<\/p>\n\n\n\n<h3 class=\"wp-block-heading\">Ignoring Recommended Coolant Levels<\/h3>\n\n\n\n<p>The engine cooling system has a &ldquo;full hot&rdquo; line on the reservoir, and this is how you tell if it&rsquo;s low or too full. If it&rsquo;s too full, it&rsquo;ll just push coolant out. If it&rsquo;s too low, you need to add coolant, but always let the engine cool so that there is no pressure before opening the system and adding coolant.<\/p>\n\n\n\n<figure class=\"wp-block-image size-large is-resized\"><img loading=\"lazy\" decoding=\"async\" width=\"1024\" height=\"702\" src=\"https:\/\/www.carparts.com\/blog\/wp-content\/uploads\/2024\/07\/photo-of-a-coolant-reservoir-fill-range-1024x702.jpg\" alt=\"photo of a coolant reservoir fill range\" class=\"wp-image-109953\" srcset=\"https:\/\/www.carparts.com\/blog\/wp-content\/uploads\/2024\/07\/photo-of-a-coolant-reservoir-fill-range-1024x702.jpg 1024w, https:\/\/www.carparts.com\/blog\/wp-content\/uploads\/2024\/07\/photo-of-a-coolant-reservoir-fill-range-300x206.jpg 300w, https:\/\/www.carparts.com\/blog\/wp-content\/uploads\/2024\/07\/photo-of-a-coolant-reservoir-fill-range-768x527.jpg 768w, https:\/\/www.carparts.com\/blog\/wp-content\/uploads\/2024\/07\/photo-of-a-coolant-reservoir-fill-range-1536x1053.jpg 1536w, https:\/\/www.carparts.com\/blog\/wp-content\/uploads\/2024\/07\/photo-of-a-coolant-reservoir-fill-range-150x103.jpg 150w, https:\/\/www.carparts.com\/blog\/wp-content\/uploads\/2024\/07\/photo-of-a-coolant-reservoir-fill-range.jpg 1600w\" sizes=\"(max-width: 1024px) 100vw, 1024px\"><figcaption class=\"wp-element-caption\">The photo is a coolant reservoir fill range. Some have cold and hot full lines. | Image Source: Richard McCuistian<\/figcaption><\/figure>\n\n\n\n<h3 class=\"wp-block-heading\">Worn Radiator Cap<\/h3>\n\n\n\n<p>Before you check the other parts of the cooling system for damage, you ought to take a look at the <a href=\"https:\/\/www.carparts.com\/radiator-cap\" target=\"_blank\" rel=\"noreferrer noopener\" aria-label=\"radiator cap\">radiator cap<\/a>. Radiator caps are designed to keep the coolant at a specific pressure. A worn cap might be loose or damaged in some way, leading to coolant spilling out even if the reservoir isn&rsquo;t too full. Your owner&rsquo;s manual should have more about how to replace it if needed.<\/p>\n\n\n\n<h3 class=\"wp-block-heading\">Faulty Thermostat<\/h3>\n\n\n\n<p>Coolant flows through the thermostat into the radiator when it hits 190 to 200 degrees. From there, the radiator cools the liquid down before releasing it back into the rest of the cooling system. The thermostat controls when the coolant flows into the radiator, but if the <a href=\"https:\/\/www.carparts.com\/blog\/what-are-the-common-signs-of-a-bad-thermostat\/\" target=\"_blank\" rel=\"noreferrer noopener\" aria-label=\"thermostat is faulty\">thermostat is faulty<\/a>, it might not let the coolant through. The coolant gets trapped outside the thermostat if it&rsquo;s stuck or otherwise malfunctioning. As a result, the radiator won&rsquo;t be able to cool the coolant down. The liquid will continue to heat up and expand, spilling out the top of the coolant reservoir as a result. Replacing or repairing the thermostat should prevent the coolant from getting stuck.<\/p>\n\n\n\n<h3 class=\"wp-block-heading\">Blocked Radiator<\/h3>\n\n\n\n<p>Like a faulty thermostat, a blocked radiator will prevent coolant from flowing through the system. Over time, rust and sediment gets trapped in the radiator and impedes the coolant flow. <a href=\"https:\/\/www.carparts.com\/blog\/how-to-clean-radiator\/\" target=\"_blank\" rel=\"noreferrer noopener\" aria-label=\"Clear the blockage in the radiator\">Clear the blockage in the radiator<\/a> by performing a <a href=\"https:\/\/www.carparts.com\/blog\/how-to-flush-coolant\/\" target=\"_blank\" rel=\"noreferrer noopener\" aria-label=\"coolant flush\">coolant flush<\/a>. If that isn&rsquo;t enough, it might be time to <a href=\"https:\/\/www.carparts.com\/blog\/radiator-replacement-101-everything-you-need-to-know-about-the-radiator\/\" target=\"_blank\" rel=\"noreferrer noopener\" aria-label=\"replace the radiator\">replace the radiator<\/a> entirely.<\/p>\n\n\n\n\n\n\n<h3 class=\"wp-block-heading\">Bad Water Pump<\/h3>\n\n\n\n<p>The <a href=\"https:\/\/www.carparts.com\/water-pump\" target=\"_blank\" rel=\"noreferrer noopener\" aria-label=\"water pump\">water pump<\/a> pumps coolant through the system, so a <a href=\"https:\/\/www.carparts.com\/blog\/signs-of-a-bad-water-pump-is-it-time-to-replace-yours\/\" target=\"_blank\" rel=\"noreferrer noopener\" aria-label=\"faulty water pump\">faulty water pump<\/a> will slow or stop the coolant flow. As a result, the engine will overheat and coolant will spill out of the system. Replace the water pump if you notice coolant spilling out of the area around it.<\/p>\n\n\n\n<h3 class=\"wp-block-heading\">Leaking Combustion Gas<\/h3>\n\n\n\n<p>Combustion gas and coolant both flow through the engine, but they follow different paths that aren&rsquo;t meant to intersect. Coolant flows through passages in the engine block, cooling the engine as it goes. Meanwhile, the engine burns air and gas inside the combustion chamber, and it expels the resulting combustion gas through the exhaust system.<\/p>\n\n\n\n<p>If the engine has either a <a href=\"https:\/\/www.carparts.com\/blog\/the-top-7-symptoms-of-a-cracked-cylinder-head\/\" target=\"_blank\" rel=\"noreferrer noopener\" aria-label=\"cracked engine block\">cracked engine block<\/a> or a <a href=\"https:\/\/www.carparts.com\/blog\/what-are-the-signs-of-a-blown-head-gasket\/\" target=\"_blank\" rel=\"noreferrer noopener\" aria-label=\"blown head gasket\">blown head gasket<\/a>, the combustion gases can escape and enter the cooling system. From there, the gases will push the coolant out of the passages and back into the reservoir, which can lead to the reservoir overflowing. Inspect the engine block and head gasket for damage and replace them accordingly.<\/p>\n\n\n\n<div class=\"rsi-card\">\n  <div class=\"rsi-thumb\">\n    <img decoding=\"async\" src=\"https:\/\/cld.partsimg.com\/d_noimage.jpg\/b_white\/e_sharpen,e_auto_brightness,e_auto_contrast\/f_auto\/q_auto:eco,dpr_auto\/w_873,h_873,c_pad\/images\/rb603205_1\">\n  <\/div>\n  <div class=\"rsi-info\">\n    <span class=\"rsi-title\">The Best Coolant Reservoir Brands for DIYers<\/span>\n    <span class=\"rsi-desc\">Check out the best aftermarket coolant reservoir brands that offer reliable fit, strong warranties, and lasting performance.<\/span>\n    <a href=\"https:\/\/www.carparts.com\/blog\/the-best-coolant-reservoir-brands-for-diyers-quickref\/\" target=\"_blank\" rel=\"noreferrer noopener\" aria-label=\"Discover Your Options\">Discover Your Options<\/a>\n  <\/div>\n<\/div>\n\n\n<p>Now that you know the likely causes behind your overflowing coolant reservoir, you can take the appropriate steps to address any issues. Coolant plays an essential role in keeping your engine cool. Refill your coolant to the appropriate levels, and keep an eye on other parts that aid its flow through the cooling system.<\/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\"> 3<\/span> <span class=\"rt-label rt-postfix\">minutes<\/span><\/span>Overfilling the coolant reservoir will cause the cooling system to push the coolant out of the pressure cap. Often, an&#8230; <a href=\"https:\/\/www.carparts.com\/blog\/overfilled-coolant-reservoir-consequences-causes-and-solutions\/\" rel=\"nofollow\">Read More<\/a><\/p>\n","protected":false},"author":1651,"featured_media":108119,"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":[3754,52],"tags":[1669],"ppma_author":[2607,2985],"class_list":{"0":"post-108016","1":"post","2":"type-post","3":"status-publish","4":"format-standard","5":"has-post-thumbnail","7":"category-air-conditioning-and-heating","8":"category-diy","9":"tag-coolant-antifreeze-2","10":"entry"},"acf":{"adrotate_specific_mobile_ad":"","adrotate_specific_desktop_ad":""},"yoast_head":"<!-- This site is optimized with the Yoast SEO plugin v27.3 - https:\/\/yoast.com\/product\/yoast-seo-wordpress\/ -->\n<title>Overfilled Coolant Reservoir: Consequences, Causes, and Solutions - In The Garage with CarParts.com<\/title>\n<meta name=\"description\" content=\"Coolant keeps your engine from reaching dangerous temperatures. But what happens if there\u2019s too much coolant in the system? What can you do?\" \/>\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\/overfilled-coolant-reservoir-consequences-causes-and-solutions\/\" \/>\n<meta property=\"og:locale\" content=\"en_US\" \/>\n<meta property=\"og:type\" content=\"article\" \/>\n<meta property=\"og:title\" content=\"Overfilled Coolant Reservoir: Consequences, Causes, and Solutions - In The Garage with CarParts.com\" \/>\n<meta property=\"og:description\" content=\"Coolant keeps your engine from reaching dangerous temperatures. But what happens if there\u2019s too much coolant in the system? What can you do?\" \/>\n<meta property=\"og:url\" content=\"https:\/\/www.carparts.com\/blog\/overfilled-coolant-reservoir-consequences-causes-and-solutions\/\" \/>\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:author\" content=\"https:\/\/www.facebook.com\/carpartscom\" \/>\n<meta property=\"article:published_time\" content=\"2024-06-06T12:36:34+00:00\" \/>\n<meta property=\"article:modified_time\" content=\"2025-10-24T04:17:10+00:00\" \/>\n<meta property=\"og:image\" content=\"https:\/\/www.carparts.com\/blog\/wp-content\/uploads\/2024\/06\/coolant-refill.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=\"author\" content=\"CarParts.com Research Team, Richard McCuistian, ASE Certified Master Automobile Technician\" \/>\n<meta name=\"twitter:card\" content=\"summary_large_image\" \/>\n<meta name=\"twitter:creator\" content=\"@https:\/\/twitter.com\/CarPartscom\" \/>\n<meta name=\"twitter:site\" content=\"@carpartscom\" \/>\n<meta name=\"twitter:label1\" content=\"Written by\" \/>\n\t<meta name=\"twitter:data1\" content=\"CarParts.com Research Team\" \/>\n\t<meta name=\"twitter:label2\" content=\"Est. reading time\" \/>\n\t<meta name=\"twitter:data2\" content=\"4 minutes\" \/>\n<script type=\"application\/ld+json\" class=\"yoast-schema-graph\">{\"@context\":\"https:\\\/\\\/schema.org\",\"@graph\":[{\"@type\":\"Article\",\"@id\":\"https:\\\/\\\/www.carparts.com\\\/blog\\\/overfilled-coolant-reservoir-consequences-causes-and-solutions\\\/#article\",\"isPartOf\":{\"@id\":\"https:\\\/\\\/www.carparts.com\\\/blog\\\/overfilled-coolant-reservoir-consequences-causes-and-solutions\\\/\"},\"author\":[{\"@type\":\"Person\",\"$id\":\"1651\",\"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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