Hi this is my first post. In December I purchased a 91 f150 4.9l 2wd. It was a a decent deal. 175k. $900

For about 2 months it ran great. Then started to fall apart. I have been pretty good at keeping up with it's issues. But for about 3 weeks it's been overheating. But not while driving. After I shut off engine within 2 minutes the radiator/reserve tank start to boil over, dumping about a gallon or more fluid out.

I have changed thermostat, done radiator flush, gotten a new rad cap, and checked the water pump, all seems good. The fan doesn't wiggle or free spin when engine is shut off. The fan shroud has a couple chunks missing out of it.

Does anybody have any experience with a problem like this? Any info would be much appreciated.
Thanks
Caleb

 

Actually dumping fluid out? Wow... almost sounds like you've got a clog somewhere or the thermostat is in incorrectly. Might want to flush again to see if you can pinpoint a possible stoppage.

 

Thank you for your input. I was thinking about a doing another flush in case I had loosened things up with the first flush and clogged it. Thanks!

 

The fan shroud doesn't help matters, but don't figure it's the cause.

Going to assume you got the right stuff - IIRC, 195degF thermostat, 13psi radiator cap, running a 50/50 mix of antifreeze.

Is your system holding pressure while hot - is the upper radiator hose 'tight', not easily collapsed by squeezing?

Any chance the lower hose is collapsing due to the suction of the water pump, impeding flow? Can you tell whether the water pump is moving the coolant, thinking of a worn or failed impeller? Are you sure the radiator core is clear and able to pass the amount of coolant?

Does the fan pull plenty of air, and are the radiator fins clear from debris and the like?

Possibility of a bad-out-of-the-box thermostat, not fully opening? Not knowing your level of expertise, any chance the thermostat was installed upside-down?

Hope this helps, keep us posted.