When it comes to radiator pressure caps, it is easy to justify just slapping one on there that fits. After all, it keeps the pressure in right? Don’t be so sure. Buying the right radiator cap is crucial to the survival of your engine. Here is why you do not want to buy the wrong radiator cap.
Too Low Pressure
If you buy a cap that is rated at too low of a pressure, then your system is not under as much pressure as it needs to be. This may sound like it is not that big of a deal, after all, why does it matter if there is pressure in the system as long as there is coolant, right? Wrong, your engine gets hot. While most engines are designed to run at around 200 degrees, this is the temperature of the coolant, not the metal. The metal is substantially hotter and can boil the coolant. The pressure in your system is exactly what keeps this from happening. If you buy a cap that is rated at too low of a pressure, then you may not see any steam, but you could be boiling coolant. This is bad for your car, the environment, and your wallet.
Too High Pressure
So, then just buy one that is rated higher, right? Nope, sorry, but buying a radiator cap that is rated too high is just as bad, if not worse than buying one rated too low. The point of having a pressure rating on your cap is because it is a sacrificial part. If your system gets too hot and the pressure gets too high, then the cap will release the pressure. When you buy a cap that is rated too high, it is not able to release until that pressure is reached. The problem here is that the other components were not designed for this pressure. Since the cap is sacrificial, this means that one of your hard parts or hoses is more likely to fail due to the extra pressure. At this point, a simple repair becomes potentially much more expensive.