My 1990 E150 van with a 351W overheats after about 15 minutes of driving. It rises to the midpoint after about 5 minutes and stays there until I get to about the 15 minute point. then the gauge goes slowly almost all the way over. Then when I park and turn it off, in a few minutes the pressure cap begins pulsing and releasing water & steam. Blows less than a half gallon of water off. Van has 68000 ORIGINAL miles.
I have already done the following:
New thermostat.
New radiator cap
New serpentine belt, and roughed up the pulley surface on the water pump pulley.
New oxygen sensor
Put on a known good fan clutch from another van w/351W.
Put on a known good radiator from same.
Flushed out the block & radiator with a garden hose, in both directions.
Used a block checking kit (The NAPA one with the blue fluid) to check for head gasket leaks.
Today I took off the water pump, and it is in perfect shape- impeller just like new.
In addition, I changed the plugs, wires, cap & rotor before this problem started.
I'm at a loss for what else it could be.
Any help will be greatly appreciated.
Tom