Ok so i have a problem.  I have an 89 chevy 4x4 3/4 ton pu.  It has a TBI 350.  Bought the truck from a friend i am pretty savy on 350s i just cant figure out.

The truck had a bad radiator when i got it, my friend i got it from had replaced water pump he though that was the prob.  He put 4 bars stop leak in it total he says. As soon as i got the truck i put a new radiator in it.  Still overheating, so took the thermostat out.  Still over heating, clutch fan really loose replaced.  Still no differance.  Replaced radiator cap and hoses. Still no difference (old hoses needed replaced anyways).  Some times it will run like 190 or so then just shoot up and over heat.  It has gotten really hot my frined said (redline) when he had it.  But not for too long.  It had boiled over on me and when it does the top hose is super hot and the bottom one is cool to touch.  No condinsation in oil or oil cap.  Starts great tells me not a headgasket.  What i would like to know is there something i am overlooking?  Somewhere in the block that may be plugged from stop leak? Bad water pump?  any help would be greatly apprecaited, i have 3 mechanic friends stumped  

you have 3 mechanic friends stumped?  you didn't even mention a blown head gasket, cracked head, bad manifold gasket or cracked manifold.  if none of the stuff you already did worked then these are you next choices.  shitty for you.  i mean there is really nothing else, unless it was you thermostat and you put the new one in upside down which is very unlikely, I'm sure you didn't  

wow hate to be you right now look into puting new gaskets on and look at your intake and heads oh and leave your return hose off and thermostat OUT plug the radiator with a cap or rag just see how much flow of water you get..sorry man good luck with that tbi pos  

Heater core plugged? Coolant in oil? Doe's the coolant circlalate with the cap off? Keep us posted WIEDER  

I have had one with blown head gaskets.  Just doesnt seem like it.  It has no coolent in oil at all and nocondencation on oil cap.  and the coolent system holds pressure.    

oh and it starts and runs awesome just over heats  

Ok. Your buddy put four cans of stop leak in the motor? My guess is, all that stop leak has clogged up one of the water passages so water can't flow properly through the block.

First, put a new thermostat in the truck. Then, when it's running, form cold to hot check the upper radiator hose. When the motor gets up to temp, the hose should be filled with coolant and you can't squeeze it shut. If you can, then you've got a coolant flow issue.

After that, I'd start with doing several good flushes on the cooling system to try and get all that accumulated stop leak out of the engine.  

Remember now don't forget the heater core!  WIEDER  

a plugged heater core will not make that truck overheat!  

Say what!Do you understand how they work? Somebody help me!      WIEDER  

If he put all four cans of stop leak in at once then it may have clogged the block.

Or, since it jumps in temp after running at 190 "for how long at 190"?

It could be a ball of Bars Stop Leak floating in the block of water pump passage. Just like having a ping-pong ball in the gas tank.

Removing the Thermostat will always make it run hotter it is not a good idea to remove it.  

I have about a million thoughts on the subject. I am wondering alot of "why's" why did your friend think it was the water pump? why did you think it is the radiator? why did the truck get a total of 4 bars of stop leak??? Is it leaking and if so where?

 I was wondering if the intake manifold has ever been off the truck? and the reason why is cause they have metal restrictor plates in the gaskets and if the restrictors were placed in the wrong position it will make it overheat and it will drive ya nuts trying to figure it out. If the intake has been off let me know, I got more info about correct restrictor placement.  

Sounds like you need to flush the system really good first to try to get all the stop leak out and good luck doing that. And when that doesnt work ask your friend why he put 4 bottles of stop leak in it. And after he gives you that answer knock him upside the head and tell him he is stupid because you are probably going to have to tear down the motor to get it all cleaned out. The only other thing you might try is bypassing the heater core and see if that cures the problem if it does then your heater core is stopped up and not letting the water flow properly. Good luck and remember take a big bat with you when you ask your fiend the question  

I respectfuly disagree with the heater core theory. I know that a plugged heater core will not cause that truck to overheat. There should be a heater controll valve which blocks the flow of antifreeze through the heater core unless you turn the heat on. They do this to keep the heater box from gettting smoking hot when you don't have the heat on especialy in the summer when you are trying to use your a/c.
 I have been working on cars for alot of years and never seen a plugged heater core make a car overheat.  

I agree at this point that all the stop leak may be causing major problems with that engine but I don't think it is the source of the original problem because the truck had a problem with overheating before that stuff was installed. It would be hard to make this statement with total confidence because I don't know the whole story about the truck.