Impatience Might Kill Me Yet

December 5, 2007 9:13 AM

One malfunctioning fuel pump + one fuel pump with a broken positive terminal = ? How safe are electric motors immersed in gasoline, anyway?

I picked up a used EFI fuel pump over the weekend for a few dollars and in the process of installing it, the positive tab snapped off. Soldering wasn't really an option because there would have been no good mechanical joint to brace the solder. So I took the two apart and made a frankenstein out of the two. So now I'm sitting here, having listened to it whir being powered by a PC power supply, wondering if I should trust this inside a tank full of highly flammable liquid. Am I insane? Or is this fairly safe, considering these things go bad inside of tanks all the time without catastrophic results? From powering it up I think it would be fine at the beginning but, if there is some misalignment from it's mutilation, it may heat up from the friction.

Other than a bit of impatience at having to wait a week for a replacement, I'm rather interested in seeing if this worked. The fact that no parts place accepts a core for this pretty much tells me they're not supposed to be repairable.

posted by IronLizard to travel & transportation (7 comments total)

As I understand, it's the gasoline vapors + air that are dangerous, so fully immersed should be fine. Mostly empty tank, perhaps not so. I say replace it.
posted by jquinby at 9:22 AM on December 5, 2007

2nding the fumes + air

you can put out a cigarette in a cup of gasoline i have seen it done
posted by BSummers at 9:40 AM on December 5, 2007

I was told by a mechanic that the fuel system runs in a vacuum. Vacuum = no fumes = no combustion...
Secondly, Mythbusters proved it was extremely difficult to set liquid gasoline on fire. :)

(I am not a mechanic)
-AltReality
posted by AltReality at 10:11 AM on December 5, 2007

oh..another note..my fuel pump blew once...I took it out of the tank...the hot wire was exposed and actually had some black charred spots on it....but my tank didn't explode.
posted by AltReality at 10:15 AM on December 5, 2007

With over 25 years of experience I can safely say I've never seen a car fire caused by the fuel pump in the tank. Electrical and exhaust issues, on the other hand, I've seen plenty of.

That said, I wouldn't put a used fuel pump into my tank unless I absolutely had no other choice. When they fail, you're not going anywhere. Unlike a fuel filter, there's no way you're going to replace one on the road.
posted by tommasz at 11:42 AM on December 5, 2007

I was told by a mechanic that the fuel system runs in a vacuum.

Your mechanic lied. Through his teeth. The entire fuel system is either at approximately ambient pressure (before the pump, but with differential heat expansion causing a slight variance - ie the tank) or usually somewhere over +3 Bar (depending on type of system) post pump in the fuel line and rail (injected engines). Carb models have little or no pressure in the line, as the just feed the carb via a float valve.

The pump sits in fuel in the tank, and as it is completely immersed cannot be in contact with the vapours - the dangerous bit of petrol. Petrol also isn't anywhere near as volatile as people suggest, either. Large amounts of contained vapours can be, though.
posted by Brockles at 5:16 PM on December 5, 2007

That said, I wouldn't put a used fuel pump into my tank

I very much agree with this. The complexity/hassle/dirtiness of the job is directly proportional to the chance of me refusing to cut costs on it, usually. Changing an in tank pump is smelly, crap and dries your hands out. I'd choose to only do it once in the lifetime of the car, I have to say.

Petrol (particularly non-street grades) and exposed contact has made my hands all dry and crappy. It gets on your nerves after a while.
posted by Brockles at 5:18 PM on December 5, 2007