94 Burb With Crazy Heater Trbl

jpgaines · December 28, 2007

i have a 94 gmc burb with a prouble that 3 repair shops have yet to fix and need some serious help. The trouble is with the heater and very liyyle heat coming out of it, on high it is luke warm air. after 3 repair shops have changed the following nothing has changed; 3 temp stats, heater core, water pump, rad cap, and 2 cooling sys flushes with a prof flush system. When you look at the water amount coming back from the core there is not alot of flow at idle, at 1500 rpm the flow increaes a little but not alot. If you turn of the blower both hoses are hot, with moter on, return hose is cold. The blower is taking out what little heat the is in the line. We have even bypassed the core and no change in the flow of the line. Also now i have noticed that the temp guage will go to 200 then fall to 160 and continue this all day, it takes about 3 min for this to happen. all three mech are stumped and i am out $500. Please help, this is a burb and i have to have hot heat!!!!!!

skills4lou · December 28, 2007

Wow, that sucks. Does it have the rear heat/AC? Have you replaced the heater hoses? Are you sure that the heater door is going ALL the way to hot, and not getting stuck half way? Does the heater blow a LOT of air on high, or does it seem to be reduced volume?

papastoy · December 29, 2007

Have you replaced the upper and lower radiator hoses? If not, when replacing the lower hose, make sure it has the spring in it that keeps the hose from colasping. I believe the old hose will/should have the spring in it already, but I'm not up on whether these newer vehicles have the spring in them. How old is the radiator? Was it replaced with a good quality one or a cheap no name radiator? Same for the heater core. Did the heat work ok last winter? Does your truck have a heater control valve in the heater hose?

jpgaines · December 29, 2007

replaced heater hoses, napa heater core and both rad hoses look good and neither one is collapsing, and there is no control valve in the heater lines it is staight from the eng to the heater core and back. The old heater core was perfect, you can blow are and water through it and it looks like new. I bought the burb in march and it was very warm and really don't know if it ever worked very well. it does not have rear heat but has rear air. The volume off are goes down as it moves from hot to cold. I'm stumped and so are the serv tech's that have worked on it. I feel like i should be throwing money out the window instead. Is it possible that i could change the inlet supply line for the heater to a diff spot like on the block?

papastoy · December 29, 2007

What temperature thermostat did they install? It should have been a 195 degree one. I'd check the temp the engine is running at with one of those temp guns.

dto · December 29, 2007

temp valve working?

jpgaines · December 31, 2007

finally found the trouble. Anyone with a 5.7 should watch the quick connect at the intake manifold. It didn't break it just disolved and clogged the inside of it so much that it would only flow a little at high rpm. This is not the hose because I replaced it but the actual connect that threads into the intake. I have heard alot of people say the had broken on off when working on it, but never one that is disolving and clogging itself. Replace it with a normal hose connector and now I have great heat!!!! Just wish the other mech would have found that before replacing everything else first. This I guess is a good $500 learning experience that maybe someone else might not have to go through. Thanks for all the help!!!!