I recently purchased this truck after having it checked out by a mechanic. The mechanic checked the compression, which was 150 lbs per cylinder, and told me the truck was in great condition. After purchasing the truck, I noticed that the truck was not heating up enough, so I replaced the thermostat. After replacing the thermostat, I noticed that the truck was heating up too much when going up hills, to the point where I'd have to shut off the engine to prevent the motor from over haeting. I replaced the thermostat again, but the problem remained. I then replaced the fan clutch, but this also didn't work. Next, I had the radiator boiled out, which resulted in a significant improvement, but the truck still runs too hot up longer hills. The guy that boiled out the radiator said it was plugged up, and that it was pretty good after being boiled out, but still had a couple tubes that were plugged. A radiator shop later performed a pressure test while driving the truck and they told me the cooling system is building too much pressure, and that I either have a blown head gasket or a cracked head. However, I don't think it's the head or head gasket because there are no other symptoms of that - no bubbles seen when I run the engine with the cap off, no coolant in the oil, no white smoke, no oil in the coolant, etc. I did notice that the heater air isn't as hot as it should be. I also noticed that the top of the radiator gets extremely hot, but the center of the radiator is never more than lukewarm. It's strange that the truck began running too hot uphills after I changed the origianl thermostat. I tested the original thermostat, and it closes and opens OK. Do you think the radiator may still be plugged? Could it be air in the system? If so, how can I purge the air? I just don't want to spend $700 or more changing the head gasket to have the problem remain. Thank you for your help!

1st... I just replaced my head gasket... $92 for the set at my local autoparts store. It's not that hard.
But, before you do that crazy stuff, replace that damn radiator. Mine overheated only after I got above 45 or so.... It would idle for days without over heating. I bought a new radiator from autozone for about $140. It works great. I broke into my old radiator just for thrills ( I was bored ). It had so much gunk and corrosion in it. I could not believe the truck didn't overheat as much as it did.

Wait a minute -it wasn't overheating until you changed the thermostat the first time? Did you do that correctly? I don't advise running without a thermostat except to diagnose, but that may be worth a shot if the problem didn't exist before you first changed the thermostat. What I do when replacing the thermostat on these is jack up the passenger side so gravity will hold the termostat in, and make sure its pointing the correct way.

The thermostat is definitely installed correctly. I forgot to mention that the heater air is only warm when the engine is hot.

How's the water pump? A slipping belt may cause this problem. I've also seen the impeller, inside the pump, come off the shaft and also rust to almost nothing. Both conditions will cause both the overheating and the poor heat from the heater, as there is insufficient flow through the engine, rad and heater core. Let us know how you make out!

I'm pretty sure the radiator was the cause of the overhaeting, as I replaced it and the truck runs cooler. Now when I go up long hills, the needle gets up to about 5/8, which still seems a bit hot to me, but I'm not sure, as I just purchased this truck. I have a request of all 1988 (or around 1988) B2200 owners: Please reply with how hi the temp needle goes on your truck after climbing a long hill. Thank you very much!

half way up (Arizona)