Getting too hot at idle

[454cid]

I had a thermostat in my '83 RX-7 stick closed once. I caught it in time and shut the motor down. I replaced it the next day.

When I was a Nissan dealer technician, a 4,000 mile Altima on the used car lot had a thermostat stick closed on a test drive. The salesman tried to drive it back to the dealership. It got so hot the distributor cap melted, which finally shut the car down. It got a new motor.

Those are problems with the thermostat itself, Though, which is not what Shurkey was saying. I too have had a thermostat fail closed. It was in my 4.0L 89 Jeep Comanche. More commonly, I've had them fail partially open. My Saturn and Volvo most recently.

 

[Wendell Mullan]

I had the same issue with my 95 K2500 Suburban, now if it was in park or neutral it would never over heat, I live in Phoenix so overheating can be a issue during summer months, what I found later on was: 1 the water pump was incorrect and was the wrong rotation, 2 the aux fan was pulling not pushing the air, 3 the ac pressure was too high. After all of that I still replaced the clutch fan set up with a flex a little dual fan system, I did have to get a 300 amp alternator as well but in traffic the beast runs at 210 degrees at 113 degrees outside with the ac on

 

[John Moore]

Hey guys just an update:

I had my radiator/AC guy replace my entire AC system. Condenser, drier, compressor, hoses, etc. The condenser was original, and what I thought to be relatively clean, apparently was not.

I had him pressure test the cooling system and circulation, all was great.

It has been idling for over two hours now and has not gotten over 200 degrees. AC is ice cold and I could not be happier.

The real test will be the 100 degree days. It was 90 today, and it was idling for hours in ~85 degrees or so. Before it would climb up to 230 even when it was 75 degrees outside.

Anyway, so far so good. The condenser that was installed looks amazing, not sure of the brand but it’s high quality. My clutch fan even sounds different like it’s not struggling to pull air.

Current temps after hours of idling:
Engine: 189 degrees
Transmission: 170 degrees
AC vent: 44 degrees.

Before the high side pressure would get over 300 psi. When tested earlier at 90 degrees, it was 225 psi.

 

[John Moore]

Update #2:

I just drove around the block and the fan clutch disengaged. Before the fan would stay fully engaged almost the whole time, even up to 5k rpm.

It is A LOT more efficient cooling now. I am very happy!

 

[alpinecrick]

Here's an idea. Borrow a pressure tester, from the autoparts store, and pressurize the cooling system. You may have an external leak somplace that you're not seeing. Coolant leaks often dry when they're small because of the engine heat. It may even be the weep hole on the bottom of the water pump, which you'll likely have to find by feel after pressurizing.

Excellent advice!
Could also be the good 'ol intake leaking to the inside--never seen it but have been told it sometimes happens.

Also....I wonder how plugged the exterior of the condensor is? Has it ever been cleaned and the tiny pebbles picked out of it (an exercise in patience to say the least). Has the truck ever had conventional coolant mixed in with DexCool any time in it's life (most GMT 400 have had this ignominy done to them by unwitting owners or even mechanics in the past)? Has the cooling system ever been flushed?

The radiator on the first few years of GMT400 production was barely adequate for the 5.0's and 5.7's, but after that the cooling system is MORE than adequate. If it's overheating it ain't a design problem.

edit: I see the OP resolved his cooling problem! I should've read the entire thread Plugged up condensers are something often overlooked.

 

[L31MaxExpress]

The stock serpentine condenser is terrible. Get a thinner parallel flow. Alot more airflow for cooling and the ac will be colder. The stock condenser design is awful!

 

[Vanishing Point]

Dear L31MaxExpress, you wouldn't by chance happen to have any (photos) or part numbers available for the thinner parallel flow serpentine condenser that you mentioned in your post?

 

[L31MaxExpress]

Dear L31MaxExpress, you wouldn't by chance happen to have any (photos) or part numbers available for the thinner parallel flow serpentine condenser that you mentioned in your post?

Part number is going to depend on which GMT 400 you have. Factory R12 and R134a systems use different threads. Also trucks and SUVs with front only air are different than SUVs that have rear air. That is the parallel flow on my Express it is a CSF. Trans cooler is made by Long, it is a M7B.

You must be registered for see images attach