hi guys,
I've got a bit of a puzzling problem i was hoping you could help me solve. I own a 1995 bronco with a 5.0. I just recently completed my motor swap into a fresh 5.0. along with a new water pump and radiator. The donor motor is a 5.0. H.0. out of a 1988 Lincoln. My question is why is my cooling system pushing coolant over the top of the overflow tank? The coolant in the tank is ice cold and the upper radiator hose is luke warm and the lower is cooler than that. The thermostat is new too. The truck does this without overheating. The temp gauge stays on the "O" or the "R". I have the supercooling package and the larger fan if this helps. I tried some of that blue devil stuff and it didn't seem to work, even after i drove the truck with no thermostat in it. Still puked the fluid out, at least the coolant was hot this time. I can idle the truck all day long and it won't happen, it only happens if i drive it for awhile. If i can't figure this out i'm going o have to scrap the truck and I really don't want to do that. Any help would be greatly appreciated guys. Ths truck is my daily driver.
p.s. sorry about leaving a long message.

 

Pushing the coolant out as it does now is the classic sign of a blown head gasket. It can idle all day but if you race the motor or drive it as you have will have the same result.

Have you tried a compression or pressure test to confirm the bad news?