'79 F150 battery drain, gas overflow

ford
gasoline
batteries
f150

#1

I have an 1979 F150, 351 V8, only 104,000 miles. Been driving it sporadically, had it serviced over the years, been driving it until recently. At least three new batteries have drained to dead in short amounts of time. No one seems to be able to pinpoint the trouble. any ideas??



It has two gas tanks–the original tank overflows out the filler cap in hot weather, even when mostly empty. I must find this trouble. Again–it’s been seen by several repair shops, but no one has fixed the problem.

Helpful suggestions are welcome.


#2

Your fuel tank sounds like it isnt venting properly…Did anyone look into the tank vent as an issue bec that is one place I would look into. They need to vent when you are filling it up with fuel…and it could also be as simple as a kinked filler tube or an obstruction in the filler hose…I’d check the filler tube for anything FIRST as it is easiest to do and the tank vent system second…its either one or the other causing this.

The battery is most likely being drained by your alternator. Try this…fully charge your batt…then disconnect the hot wire to your alternator and let the truck sit…go back a few days later and test your batt voltage…if good reconnect the alternator hot wire and start the truck. If it starts and has voltage…you just found the culprit. The alternator…if it is STILL dead…then you need to charge the batt and then pull the neg batt clamp and put a multi meter in between it and gound and measure amp draw…then begin pulling fuses one by one when you draw stops you found the problematic circuit… The most common culprit is your alternator however.

Make sure you shield that hot wire after you take it off the alternator…you can tape it up or something to prevent it from grounding out anywhere.