Old gas in the tank--Truck won't start

We had about a gallon of old gas (probably from the lawnmower) in a container and were trying to find somewhere to dispose of it (not easy). Someone suggested to simply add it to our vehicle’s gas tank, which is what we did. Alas, the next day, the truck (2000 Ford F150) wouldn’t start–that was almost a week ago. Our mechanic has been trying to diagnose it but no luck so far. At first he thought we’d need to replace the fuel pump, but since there is pressure in the pump, it seems that’s not the problem. We added gas treatment and the temperature has been regularly well above freezing, so ice in the gas tank also isn’t the problem. Help!

I’d first drain the tank, since clearly adding that gas to it had something to do with your troubles.

Unless the tank in the 150 was empty when you added that old gas then the old gas is not likely to be the problem.

There is no way of making much of a guess as to what the real cause is because what is missing, spark, fuel, or a combination of the two (they’re related), is unknown.

Spray some aerosol carburetor cleaner into the intake and attempt a start. If it runs for a few seconds then it’s a lack of fuel problem. The lack of fuel could be related to the pump or its controls and this is where the diagnostics start.

Making a sheer WAG out of the blue I might take a stab at a bad fuel pressure sensor or the control circuit for that sensor.

As usual OK4450 is right on the money…HOw many X have I started a post with that comment? Oh well give props when props are due is my motto…

YES like OK said…how much fuel was in the truck to begin with, because if it had 1/4tank or more this amount of stale fuel would do nothing to you…now if you were seriously foolish and added this to an empty truck tank then you are asking for trouble…so which is it? Its rather important.

The truck should have started regardless since the lines and filter contained the same fuel it was running on when it was shut off…If it was the nasty old gas, it would have run for 3 or 4 minutes and THEN quit…Blaming the one gallon of old fuel is not the problem…See if the truck has ignition.

I assumed the truck was running perfectly well before they added the bad gas and they just threw it into a near empty tank. If not, it is like saying “I forgot to comb my hair this morning and now the car won’t start…”.

Thanks for all the comments. The gas tank was almost full when we put in the “old” gas; and it was running perfectly before then. We’re wondering if our mistake was to put the old gas in on one day, but we didn’t try to start it until the next day. The engine turns over and seems to want to start, but it just won’t catch. We had to have it towed. It’s been in the shop since Tuesday with no luck.

The other comments are totally on point, knowing that^.
Adding that little bit of fuel shouldn’t have caused it to die like that. Something else is wrong.
If it has spark, its timing is right, has fuel pressure, working injectors and air it should do something. It may not run perfectly because of other parameters but he should be able to get it close to starting and get an idea as to what’s wrong.

I can’t imagine a good mechanic not checking basics like that. A car that doesn’t start at all is a lot easier to fix than a car that once in a while does something weird.
Have you used this mechanic before?

Actually, my husband just told me that the day after putting in the old gas, the truck DID start, but it only ran for about a minute and then stalled out. Since then, it turns over but won’t start at all. We’ve used this mechanic for many years; he is well-known and trustworthy and, I believe, has checked all the things mentioned in the last post. The only thing we haven’t done yet is drain all the gas out of the tank.

Sounds like the “Gas” you poured in was water or some other non-fuel liquid…

Your mechanic should be able to open the fuel line at the fuel rail, jump the fuel pump relay so the pump runs continuously and pump out 3 or 4 gallons or until nothing but clean gasoline comes out. Change the fuel filter, button it up and you should be good to go…

One gallon of rotten gas is not going to cause a truck with a near full tank to refuse to start unless, as Caddyman mentions, that gallon was water, etc.

There’s still not enough info to even make a wild guess. The only reason I mention the fuel pressure sensor is because they have been known to be a problem now and then.
The sensor replaces the former check valve in the fuel pump which maintains residual fuel pressure when the engine is not running. The sensor acts up for whatever reason and no fuel is going to get past it and to the injectors.

The mechanic has had the truck since last Tuesday and by last Tuesday he should have at least been able to give you a vague idea of what the problem is and what’s missing. (Missing meaning lack of fuel, lack of spark, etc.)

I vote for water, a dead stall after a few minutes of running sounds like water got in the tank. So the drain/clean option is needed.

AMEN…I would strongly suspect that the “old gas” was probably water…or perhaps diesel? LOL…methinks water is more than likely. NOW THAT…would do what was described.

Pull your pressure pin in the fuel rail…put a hose on the rail and into a container…clearer the better and run the fuel pump. See what you get…the crapo will come out first if its water related.

BEST to do this after the car sat overnight and without moving it…the water/contaminant separation will be at its most distinct at that point and you have a better shot at pumping it out. Not hard to do really.

If your fuel pump only primes when you turn the key…let me know…I can walk you thru getting it to run constant via the FPR under your hood

Nothing to add to the already excellent advice. Just let me say the next time old fuel of undetermined age is lying around and someone suggests it ought to be dumped into a car, let that car be owned by that “someone”.


But the OP DID bring up a good point…Old or contaminated gasoline is VERY hard to get rid of legally…

“I took it to my local recycling center” is just a dream…Dumping it into the local “waste oil collection center” causes major problems down-stream or if you get caught doing it…

It’s a hazardous waste nightmare…You CAN put it in an open container and just let it evaporate…

Yeah I hear you Caddy…when we try to do the “right” thing it seems to get complex…or WORSE EXPENSIVE…esp when they declare the old fuel as Hazardous Waste… I’d save it for the next bonfire…or something similar…or the evaporate method works too…but that takes a good long while…No? You can also use it as a solvent or something? I have…

I get rid of my old gas by giving it to a friend of mine that works for a maintenance yard for a golf course. Apparently places like that use burn-everything heaters.

Assuming it was water, if the old gas were first pour into a clear container and allowed to separate then poured off, most of it might then be usable and OP might not be writing us. Personally, I would repeat process then throw in an additive or marine emzyne to deal with what little has remained. Otherwise, I routinely use older gasoline to either power stuff less expensive, or as an oil thinner when I rust proof cars each year. If it’s real old, and real bad, all the other good suggestions are available…