91 Ford f150 4.9L inline 6 is overheated and will not start. I need help troubleshooting the problem. Any advice is most appreciated. Thanks

Asked by Jun 22, 2015 at 08:12 PM about the 1991 Ford F-150

Question type: Maintenance & Repair

91 f150 4.9 inline 6. Started losing power
the other day, I checked under the hood and
noticed the hoses to the air intake had
fallen off. It had been in the shop and I
guess someone had forgotten to put it
back. I put them on and tightened them,
than drove it approx 40 miles. It overheated
and lost fluid from the cap (at least that is
where I noticed the majority of the fluid)
and took quite a bit of water to refill
radiator. I was at a rest stop so water was
my only option. After it cooled down I
cranked it and after about 10-15 min it
began to overheat again. Pulled over and
repeat. Top hose was hot to the touch.
While running it, I turned the heat on and it
started out hot but within a few minutes
started to become cool. After many times
driving and stopping to let it cool I made it
to an auto parts store and picked up some
radiator fluid and thermostat. Truck would
not start from then on. Haven't installed the  
t-stat yet. Any ideas/ suggestions would be
most appreciated.

4 Answers

15,370

Sounds like the overheating problem was coming from a faulty thermostat, not opening. As for not starting now you could have fried the engine. It's it home, get a gauge and check the compression while cranking. Check and see if you blew gaskets, it was loosing power before it overheated.

Going the cheaper route first and replacing thermostat! I trickle charged the battery yesterday and it fired up fine, albeit, the motor didn't sound good... But it did run. Haven't installed thermostat yet but I'm getting a lot of pent up overflow at radiator cap. Perhaps from inability to flow through? No milk in the oil yet. Will see soon. Thanks for the feedback. I'm sure more questions will be coming!

Installed thermostat and filled radiator. No visible leaks. I drove it approx. 40 miles. I stopped and started it a few times and it would crank up fine, just didn't have the power it used to before the overheating. On the way home I stopped to get gas and when I tried to crank it the battery had trouble turning the starter. After a few more trys the battery went dead. A good samaratin was kind enough to try to JumpStart it but when I cranked it the starter would not stop! Just kept turning over w/o cranking. Nothing doing, so I disconnected the positive lead. The battery wires were literally smoking! Tried to start it hours later with a jump pack and it heated it up and still wouldn't start. I am at a loss. Does anyone have any idea(s) as to what could possibly be going on?

15,370

If it's home remove all the spark plugs. Put a large socket on the pully at the bottom of the engine and see if you can pull it over by hand. If you cannot your engine is shot, burned up, kaputt, had it.

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