My mother's 97 SE7 with ~99k miles has started to over heat. She was driving in our mid 90s heat with AC on, and noticed the temp gauge near the red and what sounds like the transmission temp light come on. No new noises or anything. She stopped and waited for a little bit and restarted the Disco, with the same results. She then called me and I said don't turn it back on.

While I'm not a mechanic, we had it towed home for me to look at it. There is plenty of new looking coolant in the radiator and no obvious leaks. The engine oil doesn't look milky or exhaust white/smelly like a head gasket. The condenser fans do turn on, but one is pretty sluggish. How fast should these turn at idle with AC on? I was going to change the thermostat, but figured the transmission light probably wouldn't turn on if it's just a bad thermostat. Bad radiator? I haven't yet had time to check if there are cool spots on the radiator. Any ideas?

 

They should sound like fans, pushing a mass of air quickly, that loud. Also suspect the fan clutch is not up to par. Check it, if it turns freely (about one revolution or more) with engine off for several hours then it's time to replace. It should resist spinning even with ambient air temps in the mid 90's.

 

Will one poorly functioning fan be enough to cause it to overheat? One looks pretty weak:
Video

 

Well they didn't install two because they had piles of fan motors laying around the factory and they didn't know what to do with them.

That's gotta be fixed either way. So I'd start with the obvious and work your way up to more expensive things.

 

I would replace the t-stat and check the clutch fan

 

So both are on full blast whenever the AC is on? The ambient or engine temp doesn't have a factor at all? Will start looking into a replacement.

Does it sound like a thermostat? I figure this is less likely since the transmission light also came on. Wouldn't a bad thermostat only affect the engine? I guess they are cheap and easy enough to change might as well.

 

A/C on - yes the condenser fans will be running. Engine coolant temp does matter, 212F (as I just read in the Rave) coolant temp and those fans will come on with or without the A/C running. The trans temp light is effected by coolant temp because there is a tank within the radiator for the transmission fluid and if the radiator is hot so will the transmission fluid be.

 

So if the thermostat is stuck closed there won't be flow to the radiator and the trans light shouldn't come on though right? Does the ac condenser put out enough heat to cause the trans temp to elevate to that degree of the thermostat is closed? Seems the ac fan is the most likely source. Whenever I have some free time I'll drive it and see if there is an issue without the ac running. Theoretically the disco shouldn't overheat without the extra load from the ac if everything else is ok. The engine fan doesn't spin much at all when I try to turn it so it should be ok.

 

Wrong, yeesh. Over-thinking every possible angle is wearing me out....you know? Replacing the thermostat is what, a housing, two bolts, a gasket and of course.....a thermostat. How difficult is that concept? It's easier than deciding dining room wall paper patterns while completing a dissertation on bowel entomology during which your reading Cat In The Hat to a drooling 95 year old who needs a diaper change because their farting Clare De Lune heir Doctor! I think I'm finally loosing my mind......

 

Which part is wrong? That I'm taking a methodical approach to this instead of just changing parts to hope it's the right choice? Kind of like in Rave saying check this then that then that other thing if they check out ok. How is that a difficult concept?