I just bought a '79 F-350 that's been (mostly) sitting for 8-10 years -- previous owner was unsure.

Long story, but the tank now contains 12 gallons of fresh fuel (10% ethanol) and an unknown quantity of old fuel, probably a mixture of some that's a year or two old and some that's 8-10 years old. The fuel guage is pegged at Full -- haven't had a chance to check if it's in-op or accurate. I think it's a 20 gallon tank, but I'm not sure -- it started life as a dual-tank U-haul, with the 2nd tank since removed.

The 2nd owner, who quit driving it 8-10 years ago, sold it the the 3rd owner, a scrapyard, a year or two ago -- I forget when I towed it in. The 2nd owner wanted his engine back, so it was swapped out for a 360 from a '69 that was driven into the scrapyard at about the same time.

To the point: the thing runs fine but REEKS of old fuel. I suspect that the oil is being contaminated with unburned fuel, also. The tank & lines are contaminated, but the pump and carb are (probably) clear.

I'm being given conflicting advice, and the one I think I oughta do is the one I don't want to do if I can avoid it.

One guy suggests a couple bottles of SeaFoam, top off the tank, and run it off. Another suggests pretty much the same thing, with any brand of fuel system cleaner. Another suggests running 40 gallons of high-octane (91 or better). Another suggests ignoring it; it stinks, but it's not a problem since it runs fine.

I think I probably oughta drain the tank and eat the $30 I unthinkingly put into it, and THEN using a fuel-treatment of some sort. An oil change is definitely in order, since I have no idea if it's contaminated or how old it is or how many miles is on it.

 

It's a carbed motor most likely with out cats, so it will smell different than catylist vehicles. My suggestion would be change the oil, clean the carb, and run the fuel out. Any fuel treatment may help, but if the fuel runs burn it.

 

To tell you the truth, it probably wasn't a good idea to top off the tank in a vehicle that had been sitting for that long.

Personally, I would have taken the tank to a radiator shop to have them clean it out. I'd also replace the rubber fuel lines and fuel filter, and then rebuild the carburetor. After it ran a while I'd put a new fuel filter on it.

If you have gas in your oil, your fuel pump is probably going out. You would need to replace the pump and change the oil.

 

I didn't even check for cats. It's a all new piping -- had dual exhaust, scrapyard changed to single when they swapped engines. Anyway, it's definitely a varnishy, stale fuel smell, not exhaust.

That's me: king of the poorly thought-out ideas. I was more worried about running out of fuel on our lot than what might be in the tank itself. Now that I think about it, the fuel-guage is in-op -- it was pegged before I put fuel in it.

 

Change the oil and just run all of the gas thru it. As long as the fuel pump isn't pumping fuel into the crankcase, it should be ok and clear up.