oveheating, imagine that!

[Kenbob]

89 renex was doing well in winter but on our first warm day it over heats at idle. It runs at 210 when on the road but as soon as I cut the rpms the temp goes up. I am going to do the burp thing. The question is, since this is a sealed system, does one of those inline flush caps compromise the system. There are no leaks around it. Also, the extra fan runs when the ac is on but does not come on by itself when heat goes above 220. If there is air in the system will that keep the switch from operating properly?

Thanks all

[Kenbob]

forgot to ask: IF that flush cap is not a problem in the closed system, can I burp fro that? It would be at a higher point than the temp switch.

[maddzz1]

Have you done any work to it lately? If not, there shouldnt be ant air in the system. Have you checked the regular probs first? radiator, water pump, fan clutch

[JeffN]

check for leaves and random crapola stuck between the radiator and ac condenser, mine had a ton o crap there that made it run hotter than it should

[Kenbob]

Yes, I put in a new sending unit for the heat guage and didnt know about having to burp it. It wasnt sitting down hill so I am hoping that is it. I am more concerned about the extra fan not coming on. If their is air in the system does that keep the switch from working? And when all said and done, how much is supposed to be in the expansion tank when it is cold?

[JeffN]

If I am not mistaken, the electric fan should only come on with the A/C on

[mvusse]

If you're fine on the highway, but not when sitting still then coolant flow is not the problem, air flow is. Either the radiator has too much crud between the fins, or your fan clutch needs replaced.

[Akula69]

The electric fan will come on without the AC if the relay is installed in the bay harness, and there is a fan temp sensor installed (either in the bung on the radiator or inline with the hose). I believe it comes on at around 250-260 degrees.

[Kenbob]

Assuming it is the fan clutch. I see there are two different kinds listed: thermal or mechanical.....any opinions?

[maddzz1]

It is probally the mechanical. Trucks without AC only have one fan.

[mvusse]

Autozone only shows one, and calls it thermal. I know it fits, cause that's the one I currently have.

Advance also only shows a thermal one. Different brand, though.

NAPA shows two, both thermostatic.

 

Where are you looking?

[Kenbob]

I think It was orielly's Thermal was what I was thinking anyway. It doesnt come on hard till 170 degrees and the other being mechanical is only governed by rpms....I think I got that right.

[STERLING STINGER]

when my 88 was overheating, for like a year, i just got a 180 degree thermo

AND

i had to remove the radiator for the ac which didnt work

removed entire ac

i run a plow on it all the time and i never had another overheating problem again

[Kenbob]

There was air in there! I also sprayed out the radiator, but did not see alot of stuff came out. Burped and took for a spin. Thermostat worked like it should, and no issues today. It is 60 degrees and not 74 so not an exact comparison. I did find one other thing that I think might need attention. The top part of my fan shroud is missing. At least I think it is missing as this is my first renex comanche and all is new to me. The top 1/4 of the shroud is not there. You can see the fan blades spinning and it looks like it should be there for protection if not for cooling. It was only on close inspection that I saw that it looks like it was broken off as the break is pretty clean.

 

THanks all for the help!