Originally Posted by 89white GT
When I bought my mustang my cousin said he put a 93 cobra waterpump pulley in it And a 165 degree thermostat. So my engine barely get over 140 degrees. This won't hurt anything will it? I always thought a cool engine is a good thing.
I don't remember which thread in this forum I recently posted some info about this, but you are better off for numerous reasons to leave the stock temperature thermostat in the engine.
First and foremost is that cooler T-Stats cause increased cylinder wear.
And, the entire EEC IV system is designed to run/tune at the factory designated temperature.
The "only" time you might want to run a cooler T-Stat, is on a race only vehicle.
Here is what I found on the net. It pretty much agrees with what I read in my book.
Change (or remove) the factory thermostat
This is based on the fact that cooler air is denser, so the less you heat the air coming into the engine, the more air/fuel mixture you can pack into each cylinder. An old shade-tree mechanic fix, but it's got several strikes against it. First, you never want to remove the thermostat completely. The cooling system has been designed with the thermostat restriction in mind, and removing it will actually hurt cooling. Second, cylinder wall wear increases as operating temperatures are lowered. The stock Mustang thermostat is set for 196° Fahrenheit. Dropping to 180° will increase wear somewhat, and dropping to 160° or 140° will increase wear dramatically.
On EFI cars, cooler thermostats are rumoured to increase performance because the engine will run richer at temperatures below 180° Fahrenheit. True, the EEC-IV will richen the mixture, but staying in "warm up" mode entails more than just a richer mixture. The EEC-IV will be more conservative with the timing curves, and will never get into "closed loop" operation (where it uses the oxygen sensors to fine-tune the mixture). The result will likely be poorer drivability and _decreased_ performance. Also, catalytic converters can be damaged over time by an engine that's continually running rich.
- Don't remove the thermostat entirely, and don't use a thermostat below 180° Fahrenheit on an EFI car.