Coolant Reservoir Cap

• An engine coolant reservoir cap is a plastic or metal cover that seals the coolant reservoir tank and protects the coolant inside from contamination. 
• Non-pressurized coolant reservoirs typically use clip-on caps made of toughened plastic.
• Meanwhile, pressurized systems need sturdier screw- or twist-on coolant reservoir caps made of aluminum.
• Coolant reservoir caps are important because they keep contaminants and debris from falling inside the coolant recovery tank and affecting the quality of the engine coolant. 
• If you’re driving a vehicle with a pressurized engine coolant recovery tank and the cap is showing signs of failure, it’s possible that your engine may overheat. In this case, you need to replace the cap right away.
• The price of aftermarket coolant reservoir cap replacements typically ranges from $10 for an individual cap to $130 for an entire kit.

Your vehicle’s engine is a complex machine that needs to function at a certain temperature range in order to run smoothly. If the engine runs cooler than its optimal operating temperature, fuel consumption may increase. If the engine overheats, important engine parts may warp and come loose. In some cases, head gasket leaks may form as a result of overheating and the engine may burn oil and coolant. To avoid these scenarios, the engine is equipped with its own cooling system.

The engine cooling system is generally made of six main components: the engine coolant, radiator, water pump, cooling fan, hoses, and a thermostat. This system serves a three-fold purpose: to help the engine reach its operating temperature as quickly as possible; to help maintain the engine’s operating temperature; and to remove excess heat from the engine. 

The coolant reservoir cap is a part of the cooling system. What does it do and why is it important? Answer these questions and more with this comprehensive guide.

An engine coolant reservoir cap is a plastic or metal cover that seals the coolant reservoir tank and protects the coolant inside from contamination. This cap may contain important information, such as pressure ratings and warnings. 

Note that coolant expands under high temperatures and the coolant reservoir cap should not be opened, especially when the engine is still hot. Opening the cap 20 minutes after the ignition has been turned off is highly recommended.

Coolant reservoir caps not only keep the coolant reservoir system sealed and intact, but they also indicate the kind of coolant reservoir system they’re placed in. 

Non-pressurized coolant reservoirs typically use clip-on caps made of toughened plastic. It’s easier to find tanks and caps for non-pressurized systems because there are a lot of universal parts available on the market.  

Meanwhile, pressurized systems need sturdier screw- or twist-on coolant reservoir caps made of aluminum. Caps on pressurized systems are often labeled with specific pressure ratings. The label serves as a reminder of the type of coolant reservoir tank it is used on. 

The label on the pressurized coolant reservoir cap also indicates the required pressure rating of the cap in case the vehicle owner purchases a new one. However, coolant recovery tank specifications, as well as other technical information and service schedules, can also be found in the owner’s manual, in case the tag becomes unreadable.

The coolant reservoir is an important part of the coolant recovery system. Also known as the coolant recovery tank, the coolant reservoir is a container that holds excess engine coolant until it is needed. This tank is translucent and may have markings that allow the owner of the vehicle to monitor the level and quality of the coolant. 

Coolant reservoirs are typically located near the radiator, but in some cases, they may be mounted on an inner fender or against the firewall. 

Engine coolant is a substance that is used to regulate the temperature of the engine and protect its moving components from corrosion. This liquid runs throughout the entire engine cooling system in order to absorb excess engine heat. 

After circulating around the engine, the coolant goes to the radiator where heat is diffused into the atmosphere. Engine coolant expands as it heats up, so the cooling system needs additional space, especially if the radiator gets too hot. 

In the past, radiators used to have top tanks that allowed engine coolant to expand into. If the coolant gets too hot and expands even further, it forces its way past the spring-loaded radiator cap to relieve pressure. Excess coolant would then flow through a discharge tube into a recovery tank. 

Modern radiators do not have expansion tanks and radiator caps on top. Instead, radiators are connected to a separate recovery tank that serves both as a coolant reservoir and an expansion tank. A modern coolant reservoir tank is partially filled with air. This air allows the coolant to expand without damaging the rest of the system. 

Excess engine coolant stays inside the reservoir or recovery tank until the system cools down. Once the system goes down to a specific temperature, it creates a negative pressure that draws the excess coolant back into circulation. When the engine is off, the coolant reservoir should typically be around 30% full. 

The coolant recovery system and the rest of the engine cooling system have a huge impact on engine performance. That’s why even minor components of these systems are crucial in keeping the engine in top shape. 

Both non-pressurized and pressurized coolant reservoir caps are important because they keep contaminants and debris from falling inside the coolant recovery tank and affecting the quality of the engine coolant. 

Pressurized coolant reservoir caps serve another function aside from protecting the engine coolant. Pressurized coolant reservoir caps allow the coolant to become pressurized. Engine coolant may reach temperatures of more than 100°C before it boils. If the cap goes missing or shows signs of damage, the engine may overheat. The coolant may also fail to pressurize properly and boil over, causing significant engine damage or even failure. 

If you’re driving a vehicle with a pressurized engine coolant recovery tank and the cap is showing signs of failure, it’s possible that your engine may overheat. 

It’s very important to regularly check your coolant reservoir tank and cap to ensure everything is in top shape. For more information on service intervals and maintenance, you can refer to your owner’s manual.  

If your coolant reservoir cap is missing or broken, you need to replace it right away. A loose or cracked cap may allow dirt and debris to contaminate the engine coolant. In pressurized systems, a failing coolant reservoir cap may even cause expensive engine damage or failure. 

Constantly low coolant levels, visible leaks, and an overheating engine are just a few signs of a bad coolant reservoir cap. Once you notice these symptoms, you’ll need to conduct a thorough diagnosis first as the root issue may not just be a bad cap.  

The price of aftermarket coolant reservoir cap replacements typically ranges from $10 for an individual cap to $130 for an entire kit. This price range depends on several factors, including the brand, quantity, and the part’s compatibility with your vehicle’s year, make, and model. 

Coolant reservoir caps are typically sold individually, although sets of multiple coolant reservoir caps and kits with several other inclusions are also available. Some kits may contain a fan clutch, fan blade, coolant reservoir, water pump, and thermostat housing aside from the cap itself.

Getting the parts that you need shouldn’t be a hassle. With CarParts.com, you get to select from a wide variety of quality and long-lasting coolant reservoir caps for an unbeatable price. If you’re browsing for pats or if you’re looking for something more specific, such as a 2007 Honda Accord Coolant reservoir cap, you can find what you need on the site. 

To get started, use the site’s vehicle selector tool to indicate your vehicle’s year, make, and model. Then, you can use the search bar to find the part that you need. The advanced search filter lets you narrow down your choices according to your price range and other preferences. Get back on the road with confidence and style with CarParts.com.