Why Should Your Next Thermostat Be a Fail-Safe Model?

October 25, 2018
min read

When your thermostat sticks, it can lead to costly repairs. After all, engine overheating is the number one cause of engine failure. Letting your engine overheat can cause a range of problems from shorting electronics due to the moisture buildup to cracked blocks and blown head gaskets, so making sure that your engine stays cool is vital to keeping it alive and running for a long time.

What is a Fail-Safe Thermostat?

Fail-safe thermostats are designed to stay open when they fail. This is not a perfect solution since the system will still run hot. Since the coolant cannot stay in the radiator long enough to cool enough, it will still allow the system to heat up and eventually overheat, but you will get a lot more miles out of it. With a traditional thermostat, they fail in the closed position. This means that coolant cannot flow at all and your system will overheat almost immediately. While you will not be able to drive very long with a failed fail-safe, you can get to the parts house to pick up a replacement.

Why is it So Important?

So, why is keeping your engine cool so important? Well, to answer that, first you have to understand how thermal expansion works. As the metal in the block and heads heats up, it expands. These components are designed to expand to a certain point and not fatigue the metal. This is why your engine usually runs around 200 degrees. If it gets too hot, then it will expand too far and crack the metal. A cracked block is usually the death of your engine, and a cracked head is not much better. If you are lucky, then you may just blow your head gasket, but these repairs can be costly as well. Head gasket repairs can cost several hundred dollars since the head must be removed and inspected for damaged as well.

How Far Can You Go?

This is going to depend on a lot of factors including ambient temperature, engine size, fan speed, and more, so an exact answer is not possible. In general, if you baby it and stop to let it cool once it starts to get too hot then you can drive as far as you have to, though you want to avoid this. Extra heat cycles will reduce the life of your engine. Fail-safe thermostats are designed to get you to the nearest parts house, so expect to be able to get a few miles down the road before having any issues.

If you want to make sure that your car is going to last you for years to come then be sure to pick up a fail-safe thermostat, just in case. A failed thermostat is an unpleasant drive and quick repair. A cracked block is a new car payment.


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