After replacing the 195° thermostat with a 185° thermostat check engine light turned on

DEBORAH WALTON

MEMBER
2005 CHEVROLET CAVALIER
2.2L
4 CYL
2WD
AUTOMATIC
243,560 MILES

When my brother changed my water pump and thermostat, he put in a 185°.
My car requires a 195°.
My check engine light comes on with the bad sensor code - which makes sense.
The strange part is that if I turn off the code, it only comes back on when it's cold outside (under 50°).
Living in Florida, it doesn't happen often. So it could be off for weeks.

My question is this:
If I just change the sensor, without changing my thermostat back to a 195°, won't the new sensor keep picking up the same problem?

Note: the temperature gauge inside car works fine, so the current sensor isn't totally bad.

Oh, and a weird? Please!
If I left the code on for a week or 2, could that cause my gas mileage to be worse?

1 Reply

CARADIODOC

MECHANIC
33,754 POSTS

First you have to list the specific fault code number. There's multiple codes for each sensor, and they mean very different things.

The cooler thermostat shouldn't be causing any other problems. They have a tolerance, meaning an acceptable range of temperatures each one might open at. It's possible to have a 195 degree and a 185 degree thermostat open at the same temperature. Depending on what the Engine Computer is detecting, fuel mileage could be affected. There's well over 2,000 things the computer can detect and set fault codes for. About half of them relate to things that could adversely affect emissions. Those are the codes that turn on the Check Engine light.

In many cases, when a defect is detected, the computer knows it can't rely in that circuit for accurate information. It can "inject" an approximate value, based on the other sensor readings and operating conditions, and try to run the engine on that. The engine could run fairly well, but fuel metering calculations will only be close, not perfect, hence the increased fuel consumption and increased emissions.

Once you know the fault code number, you can go here:

https://www.2carpros.com/trouble_codes/obd2

to see the definitions, or I can interpret them for you.