AC not blowing cold AND temperature gauge pegged to the top (1 Viewer)

[KFunk740]

I think I owe an apology for using the word "pegged" incorrectly. During my last drive, it was at the very top and not moving, so I said "pegged." I've since cranked it twice to move it out of the garage and check AC levels and both time the temp gauge was normal. So it's not permanently "pegged."

I understood that from the beginning. It was indicating hot, and understandable to exaggerate it as 'pegged,' whatever that means. If you had an air bubble in the cooling system, the air heats up more than coolant would, and air around the temp sensor could lead to the gauge indicating way hot. I don't know if air bubbles tend to find their way to temp sensors in LC100s, but its common in other cars.

I do think you've either lost some coolant, or the mechanic that did your heater Ts 1K mile didn't properly top it off or bleed it properly after he did that. The repair manual says to run it a little bit with heat on, then after it cools down, set it to the upper mark on the expansion tank (its a bit ambiguous here, but somewhere between low and full). I set mine at full, and found that it always drops a bit below the full mark when its fully cooled down. It never loses any though, and you shouldn't be down below the low mark.
Your mechanic may not bother to read the manual, though.

 

[abuck99]

More likely Fan Clutch is weak and not moving enough air. Question: does the A/C blow cold first thing when you start it- (before engine heats up to operating temp)?

Scanguage or BlueDriver app can give you all the necessary info to check IAT, ECT etc.

Anyway I'd start my check there- cold engine- engine off, spin the fan clutch and notice if there's any resistance. They start loosing efficiency 150-200k.

 

[getserious]

I understood that from the beginning. It was indicating hot, and understandable to exaggerate it as 'pegged,' whatever that means. If you had an air bubble in the cooling system, the air heats up more than coolant would, and air around the temp sensor could lead to the gauge indicating way hot. I don't know if air bubbles tend to find their way to temp sensors in LC100s, but its common in other cars.

I do think you've either lost some coolant, or the mechanic that did your heater Ts 1K mile didn't properly top it off or bleed it properly after he did that. The repair manual says to run it a little bit with heat on, then after it cools down, set it to the upper mark on the expansion tank (its a bit ambiguous here, but somewhere between low and full). I set mine at full, and found that it always drops a bit below the full mark when its fully cooled down. It never loses any though, and you shouldn't be down below the low mark.
Your mechanic may not bother to read the manual, though.

OK. Back to the mechanic then since I have no expertise in this area.

 

[getserious]

More likely Fan Clutch is weak and not moving enough air. Question: does the A/C blow cold first thing when you start it- (before engine heats up to operating temp)?

Scanguage or BlueDriver app can give you all the necessary info to check IAT, ECT etc.

Anyway I'd start my check there- cold engine- engine off, spin the fan clutch and notice if there's any resistance. They start loosing efficiency 150-200k.

Yep. Ice cold when I start (and it even seems like it may stay cold when idling) but a few miles down the road and it starts to heat up.

 

[JunkCrzr89]

If you had an air bubble in the cooling system, the air heats up more than coolant would, and air around the temp sensor could lead to the gauge indicating way hot. I don't know if air bubbles tend to find their way to temp sensors in LC100s, but its common in other cars.

Given the location of the ECT sensor on the 2uz, I think the general consensus is that the dash gauge will actually give a lower than true temp reading if air is in the system or coolant level is low.

 

[KFunk740]

Given the location of the ECT sensor on the 2uz, I think the general consensus is that the dash gauge will actually give a lower than true temp reading if air is in the system or coolant level is low.

Crazy, how does that work? I did have a mildly low coolant issue once (stupid, didn't put a little hose clamp in right place after doing t belt), and my temp gauge never went up even though my heater got super hot at my feet. So yeah, I'm prone to believe that the temp gauge lies.

 

[JunkCrzr89]

Crazy, how does that work? I did have a mildly low coolant issue once (stupid, didn't put a little hose clamp in right place after doing t belt), and my temp gauge never went up even though my heater got super hot at my feet. So yeah, I'm prone to believe that the temp gauge lies.

Conceptually, it doesn't make sense to me because air heats up faster than water. In my mind, low coolant should cause the ECT sensor to read the abnormally hotter air in the system and shoot the dash gauge through the red zone even if coolant temp is lower. But that's probably why I'm not an engineer or physicist Perhaps the ECT sensor doesn't read air as well as it reads coolant? @2001LC might be the best person to shed light on this.

 

[abuck99]

Yep. Ice cold when I start (and it even seems like it may stay cold when idling) but a few miles down the road and it starts to heat up.

That pretty much confirms my thoughts on weak fan clutch.

 

[getserious]

I've been meaning to follow up. It was a "stuck thermostat." Couple hundred dollars for the repair and I've been good since August. Thanks to everyone for their help.