Fix It and keep it

After a persistent problem of my 1995 Toyota Corolla engine running too cold, even in the hottest weather, I had to investigate the problem before I had problems with the engine computer. If the engine runs too cold all of the time the engine computer is always trying to make adjustments for the engine to warm up to operating temperature which can result in poor gas mileage and a fast idle.

In another post on this website I have an article explaining another cause of a fast idle on the 1995 Toyota Corolla caused by the idle air control valve. The symptoms seem the same as they do with the engine running cold all of the time except when the IAC valve is the problem the idle remains high, but the engine is up to its operating temperature.

With the engine running cold all of the time I found the cause of that to be the thermostat. It stuck wide open so the flow of water going through the radiator and engine was never slowed enough to allow the water to heat up.

If this is your problem and you have to go get another thermostat be sure to get one from Toyota because the after market thermostats don't have the small bleed hole on either side that allows water flow even when the thermostat is closed to relieve pressure on the water pump. The Toyota thermostat costs around $25, but it is worth the extra money to keep your Corolla running strong.