hello I have a 91 f-150 i put a motor out of a 1994 full size bronco (302) I had to pull the heads to have two bolts machined out that broke off when I removed the intake (as always of 302 efi) replaced with new fel pro gaskets and new intake gaskets it run great for about two months and now I am overheating I have put in three thermostats and a aftermarket water temp gauge to make sure of actual water temp it warms up normaly till about 160 and then it skyrockets and will peg the gauge out before it stops if you rev it up a little it will start to cool down a little but don't I am not finding any water in the oil and no oil in the water it was surging through the heater core and i switched the heater hoses and that fixed that problem i have no idea what is going on so please help thanks

 

Is your upper radiator hose getting hot? Is there coolant flow down inside the radiator with the cap off and the upper radiator hose hot? Does it only overheat driving down the road, and cool off in town?

 

the top hose is getting warm but when the gauge shows like 220 it should be hot as a fire cracker and its not it is just past luke warm it gets hot at an idle and never cools down but if you shut it off for like 10 minutes when the gauge show 220 or better and you restart it it goes back down to like 195 degrees

 

I have also replaced the rad cap and radiator and water pump and upper radiator hose when you rev it up with the cap off it will suck coolant down but when you let off it will overflow the radiator. It is my dads truck and it is his daily driver so I need to get it fixed asap thanks for the help guys.

 

I wonder why the top radiator hose is not hot? As a experiment, I would take the thermostat out temporarily and see what happens.

 

Blocked passage somewhere in the coolant route, maybe even the heater core. Does the heater get hot inside?

I just replaced the fan clutch on my '85. It would overheat at slow speeds then cool off when I got it moving. The fan clutch felt normal until I took it off, then it freewheeled.

 

I dont mean to be rude but this is in the wrong section of the forums. You have a 91 in the 80-86 year section.

 

hes just trying to get answers that way he can get it fixed and have it back on the road asap(just like every other ford guy wants there truck back on the road) and figures the more ppl he asks the more options he will have to pick from and sooner he will find the prob

 

the heater only gets luke warm inside and the radiator is cool as a cucumber I was thinking about letting it run until it gets warmed up and feel the heater hoses will that tell me if the heater core is blocked?

 

Even if the heater core is blocked, no big deal as that won't stop coolant from flowing
through the water jacket.

My first suspicions was wrong or incorrectly-installed head or intake gaskets but that
wouldn't explain the rather sudden appearance of this problem.

Did you by chance change the belts to a Serpentine setup and not replace the water pump
with one that spins in the correct direction? Are you sure you got a water pump with the
impeller facing the right direction?

I agree with Franklin2, remove the thermostat and re-assemble the engine, see what
happens at that point....

 

Perhaps the pump impeller is rotted to nothing or just spinning on the shaft?
When the thermostat is finally open do you see a rapid flow of coolant in the top of the radiator?

 

when the level in the radiator changes a lot with rpm it means you have air in the system. (that antifreeze has gotta be going somewhere).