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Thermostat temperature

I have a 1999 Malibu V6 and I’m getting ready to replace the thermostat while I’m performing some other work. The car came with a 195 degreee as OEM. What harm or good would happen if I put in a lower temperature thermostat, such as a 180 degree?

Your mileage would go down, the engine may not run as well as it did, and you may get the check engine light turned on.
Why do you want a cooler thermostat? What do you know that the engine designers didn’t? Are you trying to fix an overheat concern? (If so, a lower temp thermostat won’t really help, you need to fix whatever the real problem is.)

I don’t know how sensitive it is, but the water temperature sensor for your fuel injection system is a critical input to the computer. The programming assumes the engine has a thermostat that is trying to maintain the water at just over 195. If it sees 185 degree water, it will probably not function as it should for normal operation.

Note: Putting a lower temperature thermostat on will NOT reduce the chance of overheating and it will not provide additional cooling and it will reduce mileage and will likely reduce the life of the engine.

The engine is designed to operate at a temperature of 195 or above. Installing a lower temperature thermostat will reduce the efficiency of the engine. Install the correct thermostat only.

There is no benefit to installing a lower temperature thermostat.

All good input on why this would be a bad idea.

The first thing that came to my mind was how the engine control module would react. It has some threshold for the temperature of a “warmed up engine”. If your engine operates below that “warmed up” temperature, the control module will likely be using sub-optimal air/fuel ratios and timing curves.

Does anyone know if OBD2 will set a trouble code if the engine fails to reach normal operating temperature within a certain amount of time?

Does anyone know if OBD2 will set a trouble code if the engine fails to reach normal operating temperature within a certain amount of time?

Yes, I just went through that with my wife’s car. It would not go into closed loop control and told us so. She was going on a trip in a couple of days so we just replaced both the t-stat and the temp sensor which are the two most likely culprits. Eventually I will toss both of them into a pot of water and heat them up to see which one is guilty.

25 years ago…no problem…but today…it can effect mileage…emissions…performance. DON’T DO IT.