My 1990 g-series Van, 350 motor wants to run hot after about 30 miles.

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I have replaced the thermostat. When I went to do this the bottom half of the thermostat was gone,so far I have found no particles from the old thermostat. I also replaced the radiator, checked the water pump. It also sounds like there is a leak in the exhaust manifold. It runs about 30 miles on the open rd. before it starts getting hot. If i dont tighten the cap down all the way I seem to get a little further. The fan seems to be working properly but not exactly sure how to test it except it seems to be running properly. Could the thermostat pieces have clogged the circulation in the motor causing it not to cool properly? Should I add an electric fan? The previous owner did away with the AC as it is being used as an ice cream trk. I haven't had any diagnostics run on it as of yet since I thought the radiator and other stuff would solve the problem. Could a blown head gasket cause this issue and is there any way to check other than compression check? Frustrated.

clamdog in Pensacola FL

Jun 24, 2014

2 Replies

Popular Answer

csubak30on Jun 24, 2014

If you didn't remove the other half of the thermostat...it is in there somewhere. Probably jammed in the heater core or the radiator. Last place, in the water pump.

clamdogon Jun 24, 2014

radiator has been replaced,not in the water pump checked it. Any reason why I can't bypass the heater core.

csubak30on Jun 24, 2014

You can bypass the heater core but, could get chilly in the winter....If you leave Florida and head north!! LOL!

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pushrodon Jun 24, 2014

That's strange!!!... Could try a 3 row (heavier duty) radiator... At hi-way speed... the fan is not really needed!... NEVER seen a properly installed thermostat come apart on GM and been doing this a pretty good while!... 40+ years!... Pieces should have been easily extracted..... I dont think it's a head gasket!... Is the a/c condenser still in the van?... In front of the radiator.... . BTW..... Coolant flows from the engine back to the rad through the TOP hose!!... Think about it....

clamdogon Jun 24, 2014

The AC condenser is still in place, I did think about removing it, sounds like I should. It's not doing anything.

pushrodon Jun 24, 2014

Exactly!... . I have a 1982 Beauville (same van) ..... and had the same problem once headed your way from VA.... new 3 row radiator fixed mine!!!. Now that may not be your problem but it sure sounds fimiliar!!!!... Also, since the broken t-stat pieces should still be in the intake.... should be pretty easy to get out... i would think, as the flow is trying to wash them toward the top hose.... IF it even needs to be extracted! Good luck... let us know what ya find...

clamdogon Jun 27, 2014

I replaced the radiator, fan clutch, thermostat and checked the water pump. I did end up removing the ac condenser. After all of this it still wanted to run hot. Loosened the pressure release handle on radiator cap and she cools like a champ. Did not know that a radiator cap could make a difference. Never did find the parts from the thermostat maybe clogged the heater core and this is what's causing the issue. Thanks for everyone's help. Had I not have already bought a two row rad I would have gone with the 3 row for an xtra 125.00

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