I just had a new fuel pump put in my 1994 GMC Sonoma. As I was leaving, the mechanic told me I should keep the gas tank half full to extend the life of my new pump. However, due to the language barrier between us, I was unable to determine whether he was telling me to only fill the tank half-way, or, to never let it drop below half. Which is it? Why?
He would otherwise tell you to keep it half empty.
I would recommend forgetting he ever said it.
Other than some slight chance of damage to a pump by running the tank so dry as to draw air, it should make no difference whatsoever.
The people who design fuel pumps designed them to work fine at any level of tank filling. Presumable, keeping the tank more full would make it less work for the fuel pump to maintain the required pressure. I can only guess he was suggesting that might increase its life. But this doesn’t hold water. When you factor in fuel pressure regulators fuel return lines (in the case of fuel injection), it just doesn’t make any sense. The level of fuel in the tank just doesn’t make a significant difference in the amount of work the pump has to do.
I can think of one longshot idea in the case of fuel injection. Most fuel injected cars have the fuel pump in the tank. Having alot of fuel in the tank could conceivably increase the cooling to the pump. Still a pretty weak arguement.
The best way to extend the life of your fuel pump is to not drive the car.
The electric pump in you tank is indeed cooled by the liquid
gasoline surrounding it. Unlike other electric motors with an internal cooling fan to circulate air, the pump requires the gas surrounding it, else the brushes burn out.
Refil at 1/2 tank.
NEVER go below 1/4 tank!
Not slamming you, but where did you find this info?
A couple of things seem contrary to this.
- Anyone who would design a fuel pump to rely on the fuel in the tank for cooling would be a total moron. (That doesn’t mean it has never happened though)
- Pumping the fuel THROUGH the pump, as it has to do anyway, would be a much better way to use the fuel for cooling.
Bah.
Thats too blanket of a statement to make. Many electric fuel pumps aren’t even in the tank. They couldn’t give a shit if you only had 1/2 a gallon of gas left.
Even for the ones in the tank, that advice is questionable at best. There is some sound reasoning behind it but I wouldn’t bet any money on it.
Old wives tales: Don’t run the tank low, or you’ll just suck up all the sludge at the bottom of the tank. My answer: When the tank is full, the sludge is where exactly? What “sludge”…or what “debris”?
I’ve burned out my share of “low fuel” lights and never had a gas filter or fuel pump issue. Ain’t anectodal evidence great?
Actually, if you want to make an arguement for filling a gas tank, try the “condensation will build up in empty tanks” arguement. Although, I would like that myth tossed aside.
And, when gas tanks are down to a quarter tank, even in smaller 16 gallon tanks, we’re still talking about four gallons of gas (probably more based on how gauges work).
Now all of a sudden, we need 10 to 12 gallons of fuel to properly cool the pump? Can I just put this in the “give me a break” category?
Regularly driven cars with fresh gas will do fine, full, empty, half full, etc.
Fuel pumps are at risk from old gas…but then so is your whole damn engine at that point.
What exactly is the risk from old gas? And how old are we talkin’?
Well, it doesn’t seem to be as big a problem as it used to be with old/stale gas. Maybe they are putting more additives in there to help deal with this.
Still, something odd can happen in gas that has sat along time. I am not sure if parts seperate out of it into layers or it is decomposing. End result is the same, you wind up with some jelly-like stuff in the tank. It is great stuff to plug up fuel filters and carb jets.
I’ve never seen it do any engine damage. It just required a complete cleaning of the fuel system.
Click & Clack seem to think that running the tank dry can hurt your fuel pump, or at least accelerate its dying day. Which doesn’t mean it’s true, of course. 
I was skeptical of the warnings concerning the care and handling of in-tank fuel pumps also, so I did some web-searching. I’m still pretty skeptical. Google led me to this article on how to change an in-tank fuel pump.
The bottom of the article’s second page includes a pretty good “how it works” sidebar, which among other things asserts that the fuel is in fact used to cool and lubricate the pump.
Based on this explanation, I could see how running your gas tank completely dry might damage the fuel pump, as it would be running with no lubricant at all. Running the tank merely low, however, should pose no problem.
Similarly, cooling shouldn’t be a problem except in extraordinary circumstances. According to this story, it’s the fuel flowing through the pump, not the fuel the pump is immersed in, which is used for cooling. The pump runs continuously to keep the fuel system pressurized, and excess fuel that the engine hasn’t burned is recirculated back to the tank. So there should be plenty of coolant (fuel) flow, even when the tank is nearly empty.