Hello. My sisters 1992 RS tbi runs very cold when driving 20+ mph or when the AC is turned on and idling. it runs about 110 - 130 degrees fahrenheit. This is in 100 degree summer weather as well. As long as the car is moving, it will run sub 130 degrees. But if you sit and let it idle without the AC on, the engine temperature will quickly rise to 220+ and wont cool itself unless you turn on the AC. then when you turn it on, it goes back down to ~ 120 degrees. I took it to a shop and im not sure if they could handle the problem because they didnt figure it out. They replaced the thermostat, replaced the coolant, replaced the cooling fan motor (at the time the fan had gone bad and she needed it to keep the engine from overheating because its summer. Also they said it was the entire motor that had gone out not just a relay. Thats what they say, im not sure that was actually the case but its too late at this point.) I am going to take it to another mechanic some time, i won't be diagnosing the problem myself because im not a mechanic and i wont pretend to be. I just would like to know what your guys' thoughts might be on what could be the problem. Also, how bad is it for the engine to run cold? My sister has been running it like this for the past year because she didn't realize that the engine was running cold, she only knew that the car wouldnt cool itself unless you manually engaged the ac fan. I am worried that a lot of damage has been done. But as far as i can tell the car runs and sounds very well. It is in pristine condition and only has 120k miles. Not exactly garage kept but it is always stored under an awning and is very well maintained otherwise.

 

Have you verified that the fan switch on the passenger side head is in working order?

 

will I only be able to see/access it from the bottom of the car?

 

You may be able to spot the wire for it from above but you'll have to get underneath to see it properly and access it, in between plugs 6 and 8 if I recall correctly.
I would also imagine it would be using a ton of fuel running that cold all the time.

 

I will have to check it out later today or another day but I think the shop we took it to also replaced the fan switch. I will have to take another look at the receipt but I’m pretty sure they said they replaced it. Plus, seeing as how we brought it in for cooling issues, I find it hard to believe that wasn’t one of the first things they checked. Correct me if I’m wrong, but even if the switch was bad, wouldn’t that only affect when the fan engages? It would need to be manually engaged (such as we do now) but that doesn’t explain why the car runs so cold when the AC is on or when driving. I thought it had a stuck open thermostat, that would have explained it better, but that doesn’t seem to be the case because replacing it didn’t solve the problem.