allright then, try your best to solve this one, yes its an 88 with a 2.9 and an auto, wants to overheat all the time, Ive searched for hours and hours and days and days, so Ive done my research. (I never let it overheat, Ive shut it down before it does every time) but it will overheat id I dont. let me describe the symptoms. it runs at the top line of the temp gauge, heater works very well, lower radiator hose cold, upper hot. center of radiator is cold, only warm spot is where upper hose attatches, I replaced the temp sending unit cuz it was 3 bucks and easy and worth a try, still ran hot, I tried a new thermostat, still ran the same, i got a slight smell of coolant inside truck and windows got just a little foggy, replaced the heater core (thought maybe loss of pressure caused it) still runs the same, replaced thermostat with another thermostat, still ran the same (although the new thermostat which i got under warranty looked a little WORSE than the new thermoistat I took out, tried it anyway) hoses arent collapsed and can feel pressure, today I replaced the radiator because read that if it has cold spots its likely clogged, couldnt see alot of flow, so i went for it. runs the same, upper hose hot, lower cool, radiator cool, heater good, ive burped the system for a long time, i removed the upper hose and filled cooling system there and bled again, same thing, the only part of the cooling system left is the waterpump but it looks like a sob to change and the heater is getting hot, so it has to be pumping, but i cant think of anything else it could be, unless my cap is bad, or maybe somehow there still is air in the system, or my replacementreplacement thermostat is bad, please help, stranded at work on new years eve until i get it figured out.

 

All I can think of is you may have a cracked head..

 

> the only part of the cooling system left is the waterpump

You might think about replacing the fan clutch with a new one. The 1990 has a better blade fan, if you have a junk yard close by you might want to grab it and do that swap at the same time.

 

Have you read the temp with an actual thermometer? Even backprobing the computer's ECT sensor would provide verification that the dash gauge is reading correctly.

If it really is getting hot like that, I would also look at the fan clutch.

 

If you've replaced all those parts with new parts, then the only suspect(s) left are the water pump, the fan, radiator cap, head(s), or freeze plug(s). The only other thing I can think of outside of that is that the cooling system is in dire need of a flush. Are you losing coolant constantly? Do you have a heavy coolant smell from the exhaust or anywhere else? Was the thermostat installed correctly? What have you done with changing / checking / adding fluid or filter for the transmission? Do you have an external cooler or deep sump pan on the transmission in addition to the cooler in the radiator? Are the cooler lines hooked up correctly? This overheating issue could also cause bad things for your A4LD. Another thing to check is for oil in your coolant / coolant in your oil. Could be a gasket or head. I'd also check the transmission fluid for signs of cross-contamination. Just some things to think about.

My '87 would run a little hot and I found that the block heater was leaking around the seal and that the radiator cap wasn't holding pressure. I completely flushed my cooling system, fixed the leaking block heater, and replaced the radiator cap, and that solved the problem. I wasn't aware that the '90 models had a different fan than the rest - but that might be worth looking into. I think if my fan clutch ever goes, I'll either do an electric fan with a direct temperature sensor / control or a spacer and flex fan. Depends on if I ever do a body lift or not.... hope you get it figured out