This myth is one of the worst there is, as the thermostat does not have any control over the operating temperature of your engine. Your engine is going to run as hot as it is going to run based on the cooling system parameters. A properly designed system will maintain the temperature in a safe range. The only thing the thermostat does is open and close at a specific temperature, it is actually regulating the minimum temperature, not the top end. A 160-degree Tstat begins to open around 135-140 degrees and is fully open at 160. When the temps fall below 160, the Tstat begins to close until the temps rise again. If you have too high of a tstat, your engine will get up to temp faster, but you are closing off some of your cooling range, going to a cooler temp unit will only open the flow faster.
There are reasons to run a higher or lower thermostat, such as you want to be able to use the heater sooner from a cold start, or your engine needs to get up to a higher temp faster. Most modern engine ECMs don’t even turn the fans on until the engine is at 205-degrees, so going from 190 to a 170 tstat won’t do a thing to reduce the operating temperature unless the previous tstat was higher than the cooling system’s efficiency.
AS you can see, there is a lot more to cooling systems than just the raw parts, every piece of the puzzle needs to be compatible, from the radiator to the coolant and water you use. This article is a “5,000-foot view” of engine cooling systems. You can learn more on each of the above sections by clicking the links in the text above for each section. Gearheads spend the most money on their engines, why would you put it at risk by running the original 6-cylinder radiator and tap water?
