When it comes to coolant caps, there is a surprisingly wide array of radiator caps. There are different ratings as well as vented and non-vented caps to name a few. So, how do these differ and which should you use on your car?
The pressure rating of a coolant cap is how much pressure it takes to overwhelm the cap and have it release coolant. Most cars today use around a 15 or 16-pound cap. While you can get caps that go up to 20 pounds, this is not advised. Increasing the pressure too far beyond OEM specs can cause serious damage to your cooling system.
If the pressure is allowed to build beyond the safe limit and not be released, then it can cause gaskets to fail or even blow out the wall of the radiator tank. Since the radiator is designed to work at a very specific pressure, it is only designed to handle a little above that. This can cause it to fail and burst, especially around weak points like seams in the metal.
Conversely, do not get a cap that is too weak for your system. It may seem like this is an easy way to reduce the stress on your system, but this is not the case. It may seem to work fine, but in reality, it is likely causing localized boiling. Since the metal inside of the engine is going to be much hotter than the coolant, if the coolant is not under pressure then it cannot heat up enough to cool the metal. When this happens, it causes it to boil and can eventually cause your system to run dry.
Vented caps are usually used in closed loop cooling systems. This is because the system is designed not to be opened up to the air. It is meant to be under pressure while running, then when it needs to vent to allow the negative pressure to be released as it cools it draws from the reservoir tank. On a closed loop system, this tank is not pressurized and is simply for the system to draw from and overflow into during normal operation.
These are used in open loop systems. This is the system that most people are familiar with. This is the cap that actually goes on the radiator. A non-vented cap will not allow pressure to enter the system. This means that if you remove the cap and allow the pressure to be released, then you must wait until it has cooled back down before putting the cap back on. If you do not then it will create a vacuum inside of the radiator as it cools. This can be as harmful as having too much pressure in the system. It can cause your hoses to collapse of gaskets to fail, so be sure to let it cool first.
Coolant caps are a small part that plays a big role in the health of your vehicle. Do not neglect it and be sure to replace it if it has failed or your system will leak and will not retain enough pressure.
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