calypsocowboy

Hey all, brand new to the forum, I have a Ford F-150 4x4 shortbed with a 302 in it. I have recently tried putting a new thermostat in, and it wont open up at 180f. I tested both the thermostats I have, and they tested fine. But when I put it in the truck it wont open up, all the coolant in the radiator and hoses stays cold and the block gets hot, and I have had the block up over 180f. Then when I take it back out and let it free flow, it works fine, accept obviously I don't have any heat and I cant get it up to operating temp. Everything flows fine , heater works fine but I cant put the stat in. Someone told me that it could be some sort of vapor lock , like air getting in somewhere and making a pocket behind the stat somewhere and not letting the stat open. Anyone have any insight on this, Im at a dead end. Thanks

390wagon

air in the system is certainly a possibility, put a flushing tee in a heater hose, leaving its cap open a little bit when refilling will help get the air out.

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68 Ford Country Sedan Wagon-390 FE, C6, 9 Inch
87 Chevy Caprice Classic Wagon-307, 2004R, 10 Bolt, what can i say, i grew up with that car

troyboy8102

I have a Ford f150 4X4 w/ a 351W and it did the same thing, you might try jacking the front of the truck up about two feet so it will purge the air out of the system, make sure the 1/8" hole is up on the thermostat.
Some f 150"s have a valve inline on the heater hose if your's has one make sure it is working, you may have to run your engine for 15 or 20 minutes to purge it. "Good luck with it!"

jo14

I've worked on an '89 Bronco with 351W, and '90, '91, and '94 F-150 with the 302 and they have all done the same thing. Air in the system sounds like the problem, but it could be that the thermostat is in backwards. Look on the thermostat and see if there is a hole in it with a small metal ball. If there is, make sure it is on top.

wrenchman30

spring faces the engine block.