4.0 blues- Now it overheated?

[badtxz]

Trying to get this truck back on the road after 2 years. It has a junkyard motor(temp. for rebuild), new radiator and rebuilt transmission. It overheated in moderate traffic. I've pulled the waterpump of and it seems fine and the thermostat opens when you heat it up. I'm stuck!

 

[Big Jim M]

Howdy txz. Are you saying it puked it's guts out? Spilt coolant all over the palce?
Big JIm

 

[badtxz]

Yeah! it spewed. It blew the cap off the overflow tank. I'm pretty sure it didn't leak out and then overheat. It had water and a lot of pressure when I shut it off.

 

[Big Jim M]

Oh my! What a great post!

Yeah! it spewed. It blew the cap off the overflow tank. I'm pretty sure it didn't leak out and then overheat. It had water and a lot of pressure when I shut it off.

Well txz it is plain to me you have went off while half-cocked! Always before taking something apart one should KNOW for SURE what is the problem.. You seem to not have known.
Now the bad news. By far the most common overheating problem is a small outside leak. A leak that isn't noiced by the driver untill the engine overheats.
The least likely of all problems is the coolant pump!
Here's what I'd do now. You already have it apart. I'd think of the miles on that pump and I might decide to replace it. I'd put her back together and fill it with coolant (properly to make sure it is actually full).. then I'd run her around the block till it was up to temp.. Then I'd leave it running and open the hood to see if small bubbles were coming out the overflow.. If yes then that would indicate a head gasket leak.. If NONE than that would indicate what I started with...a small barely seen outside coolant leak.
For sure keep a close eye on the coolant level. If it is a leak it could be the radiator cap...a hole in the hose between the cap and the tank.. heater hoses.. even a small crack in the radiator itself.
Big Jim

 

[mosher41]

my 4.0 seems to create a lot of pressure too...i do not usually loose any coolant but sometimes it will push past the cap and on the ground and sometimes it doesnt. no rhyme or reason to this truck, it does some strange stuff now and then. yesterday is smogged my neighborhood with thick oil smoke for a little while...then cleared up ????

its a new cap too

 

[stx4.0]

Alot of people forget the obvious with an overheated/ing engine.Its not only a thermostat or coolant leak or plugged radiator but once a motor has been overheated you open the door for all kinds of ugly problems including warped heads and warped block which changing a water pump or anything else for that matter will not fix.That is what happened to my 4.0 that wasnt overheated bad but by the time I seen the temp gauge the damage was done.The 4.0 is not forgiving to being overheated like alot of other engines are so you have to catch problems right away with them or your looking at pulling the engine.I have seen at least 5 others that were overheated due to the poor thermostat that was used from the factory and all of them were warped.There a good engine but they dont tollerate heat at all.

 

[mosher41]

i agree with the heat thing...i rescued this truck, it had bad head gasket in it when i bought it, i have no idea what caused that ar what abuse the motor really went thru. I have been plagued with all kinds of issues with this motor, all of which can be attributed to heat. Mine is being completely rebuilt as we speak.

I think it is a good piece if treated like that !

 

[modelageek]

I had a 96 f150 with a 302. I had my daughters picture over the temp light/gauge.(lower left of the dash) I blew the bottom radiator hose and never noticed. I think i drove the truck for months. when I figured it out i replaced the hose and added coolant .drove for another 40k and then sold it........never had an issue........