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1986 4 x 4 Suburban


LawnSite Member
Greenville, NC
I have a 1986 Chevrolet 1/2 ton 4 x 4 suburban. The heat will not warm up unless the truck is sitting still. I have replaced the water pump, thermostat 160 degree, new heater hoses, flushed the radiator, flushed the heater core, replaced all the vaccuum lines, checked the flaps to make sure they are opening and closing properly. If the heat warms up sitting still and then you start down the road it will cool right off. Any Suggestions? I have been told that the flap inside the heater box may have lost the weather stripping that seals the box from outside air, but I am trying to make pulling the heater box a last resort.<p>----------<br>Steve Harris<br>From The Ground Up Landscaping


LawnSite Senior Member
If the engine is heating up properly, and the plumbing is correct between the engine and the core, the only think I could see being a problem is the duct work. Outside air is probably the best bet, and the place I'd look first to find it would be where the fan assmebly and coolant lines enter the cab on the passanger side. Good luck.


LawnSite Bronze Member
try installing a 180or 195 stat. When you go down the road the 160is opening to soon and not letting the coolant warm up.<br>Do you get any air moving when at speed, or is there nothing coming out of the heater? If you get air but it just cools off then I suspect the thermostat. If you get no air moving at all, then check the cool air intake.<br>Dino<p>----------<br> Professional Ice and Snow Management <br>Products:Services:Equipment www.sima.org

Chuck Smith

LawnSite Senior Member
Nutley, NJ
Bingo Dino. I run 190 degree in both my 77 Chevy and my 80 GMC. No problems with heat.<br>Also no problems with overheating in the GMC when plowing. Considering it only has a 3 row radiator.<p>~Chuck<br><p>----------<br>Chuck's Chevy Truck Pages - Snowplowing Central<br>http://members.aol.com/csmith669/plowcentral.html