1990 Chevy truck overheating

[Trev72]

Hi, I'm new to this forum, and I'm hoping someone can shed a little light on a problem I'm having with my recently acquired 1990 Chevy 3/4 ton 350 V8.

After about 10-12 minutes of idle, the engine overheats, so I turn it off. The first thing I did was replace the thermostat. Fired it up again, still overheats. The rad hose isn't hot, except for near the thermostat housing, which seems odd. No visible leaks from the rad, and the rad is new, belts and hoses are new. I also have a brand new heater core that I am going to install this week most likely, so I'm wondering if that has anything to do with the problem. I've been reading a few other threads, and a lot of people with a similar problem have had it suggested that they check the fan clutch. I haven't checked the water pump, but I suppose that could be a possibility as well? Could it be an issue with the rad? What throws me off is that the rad hose is still cold, like I mentioned, but only hot near the t-stat housing.
Any ideas on what this issue could be?
I haven't bothered flushing the system and putting fresh coolant in yet, because I just wanted to get it running and to see if I could solve the overheating problem.
Thanks for any help and info

[silverhairdeere]

did you flush the radiator before putting it in , you wouldn't never believe the junk that could be in a new one , it could also be air trapped in the system , and lastly check your water pump with the belt off for looseness , and just because it's a new thermostat don't mean it's good .

[myteemyk]

Hey Trev, Welcome. I'm still a Newbie too.
I'm having a similar problem on my 76 350. Rad is always low (about half). My coolant seems to keep dumping into the overflow tank. I thought my thermst was bad, but it slowly warms from housing to rad, but never a firm solid flow. I was told once norm temp you can squeez the upper hose and should feel a surge upon releasing if the pump is working. I've tried that and not much of a surge.Feels weak. I've let idle with rad cap off and slowly filled with coolant, but boils out. I don't see a lot of circulation. I don't know if it's my pump, thrmst or possibly rad cap isn't holding correct pressure and letting the cooland escape. Maybe I can learn something with ya. My temp gauge doesn't work either. Somewhere in the wire or gauge itself

[bradrhale]

id pull the radiator cap off and see if you have flow, which i doubt. pull the lower radiator hose and dump water in to the radiator. how quick does it exit out of the lower port?? if very slow or doesnt, then you probably have a clogged radiator. being that the hoses are cold, we are going to say that you are getting good transfer so a new fan clutch or clogged radiator fins would be out of the equation. at this point, considering you didnt install the tstat upside down, would be a bad pump.

[zombie1969]

You didnt put the thermostat in upside down did you?Not sure how your heater hoses are routed but mine has one going to the radiator and you can see coolant flow right away so I know its flowing through the system and the thermostat should have a small hole that helpes purge air out of the block.

[Trev72]

Thanks for all the input. Gonna do some work on it tonight with a friend, and take some of your suggestions into account and see what we can find out. I'll post an update after the fact.

[Trev72]

So this is what my friend and I did tonight...

Upon arriving at the truck, we fired it up and let it idle. We squeezed the rad hoses and felt no surge in them. This led us to believe that we needed to replace the water pump. So we went out and bought a new pump, then came back and took out the old one and installed the new one. 2 1/2 hours later, with only flashlights, and after a quick check by the cops to see what we were doing, we fired it up and let it idle for 15 minutes - no overheating, hoses were hot and coolant was flowing nicely! So that seems to solve that problem. Now I'm gonna move on to the heater core and a few other minor things after I move it to another friend's house where we can work on it.

Thanks for all the advice, it certainly helped.

Trevor