Overheating

Hi gsfeltner,

Thank you for the donation.

If the cooling fans are working correctly, then the most probable cause would be a stuck thermostat.

Start engine and run for five minutes. Feel the upper and lower radiator hoses. If the upper hose is very hot whereas the lower hose is cool to the touch, then the thermostat is most likely stuck.

New thermostats are known to fail as well. You should check it again.

You have gone through everything so the last thing to check would be the water pump. If the pump is bad, it would not be pushing the collant through the system.

Remove the thermostat and run vehicle without it to test if it is the cause of the problem.

I am going to add some information, as I have been following the post. Before I would invest anymore time or money, I would have your cooling system checked for the presence of combustion gases. By and large, most Northstar cooling system problems are the result of internal leak, especially if there are no external leaks/low coolant. Often times the higher the load, the more super-heated combustion gases are introduced into the cooling system. What happens is the result of poor design. Through the extreme torque placed on the head bolts, and expansion and contraction of metals, the threads (aluminum) in the block end up failing. The repair involves engine disassembly, and steel thread inserts installed to replace the original aluminum ones. In twelve years, I have yet to see a repeat failure after the repair has been done, and done properly. Hope this helps.