I recently did an engine replacement in my daughters 2008 Ford Fusion. The engine I installed was completely overhauled. New bearings, seals, rings, head tanked and new valve stem seals, checked for warp across the head surface, new water pump, thermostat, cylinder head temperature sensor, new coolant temperature sensor, new radiator, and heater core flushed. With all that above done and engine installed, it starts up and runs great. However, in taking the car for test drives to make sure it functions as it should, the engine will sporadically overheat. It sometimes will only take a matter of driving the car a few miles while other times it takes up to 20 miles for the engine to overheat. The following has been done in search of the problem. A compression test, a cylinder leak down test, a blown head gasket test ( used kit with blue liquid ), replaced the degas bottle cap ( coolant reservoir, and inspection of connectors to cylinder head temp sensor and coolant temp sensor. The cooling fans are working properly and turn on when the should. I am stumped as to what could be the problem. The only remaining thought is that the impeller on the water pump begins to slip as it reaches operating temperature. Has anyone in this forum experience such a problem? And as far as filling the cooling system goes, I used a coolant evacuation kit to put a vacuum in the system to fill the system up with coolant. There are no air leaks as the system will hold a vacuum prior to filling the system with coolant. Any info on this issue would be appreciated.

 

My first question is , are you sure it is actually getting HOT or could it be an electrical problem with the gauge?

 

The temp gauge seems to be working just fine. There is hot air being blown into the cabin after the engine warms up. But, after I get it out on the road to test, when the temp gauge does rise above the normal operating range it's not gradual. The gauge needle will get pinned on H and along with it the air in the cabin gets cooler. Raise the hood to check for leaks and there are none. But, the degas bottle ( reservoir ) has the coolant near the top of the container. The radiator hoses are warm/hot to the touch as are the heater core hoses. Spinning the degas bottle cap loose some there is pressure in the system and the top radiator hose is under pressure. So you know, after going through the same routine a few times I used the small hose next to the cylinder head to burp air out of the system. There wasn't many air bubbles that found their way out. I have drained the coolant a half dozen times and refilled after evacuating the system of air. Each time I have only been able to get the system to accept about 7.5 quarts of coolant. The specs on capacity is that the coolant system is suppose to take up to 9 quarts. So, I am also trying to understand why the system won't take the called for capacity. Engine runs fine without hesitation, no evidence of coolant in the oil or trans fluid, no gas bubbles observed when blown head gasket test done and no change of color in the test fluid, all cylinders have good compression, and the rings seem to have seated fairly well. I left to think that the water pump impeller is slipping, my serpentine belt is slipping ( it's got good tension on the pulley's), or I have a faulty thermostat. It's frustrating as the water pump is new as is the thermostat and radiator. No blockage should be anywhere in the system. I even had the cylinder head tanked and checked for cracks prior to assembling the engine. Really don't cherish the thought of removing and replacing the water pump. Clearance is tight between the fender well and water pump shaft. Only other thing I can fathom is that the PCM needs reprogrammed after a engine R&R

 

Have you considered removing the thermostat and see what you get?
Engine should get warm, but not HOT.
~~~~~~~~Defective temp sending unit checked out ?