Quite a few years back this truck blew the expansion tank so explosively it took the neck off the radiator too. But there was a good explanation after I figured it out:


Ex-wife was and is clueless about cars and had been driving it on hot summer days. She told me after it happened that the AC blew warm air whenever stopped in traffic but it got cold again once at road speed. The actual original defect was the clutch fan had failed, which then overtaxed and burned out the electric pusher fan in front of the condenser. Idling through a parking lot and BLAM!.


The easy solution was a complete rad/condenser/electric fan from a wrecker as well as a new fan clutch.


It probably was borderline overheating at every stoplight.

After a good long drive this evening I checked the hoses to the water valve and they were barely warm. Inlet a little warmer than outlets but not as warm as I would expect.


This thing has an auxiliary electric water pump. Maybe it's failed. I'll check that next.

Old enough m54 has aux water pump and whrn that fails you will have terrible cabin heat. It's below the intake filter.

Cheapo from Amazon incoming. ;)