Ruining An In Tank Electric Fuel Pump?

My understanding of the most common cause of failure for in tank fuel pumps is lack of continued operation with LOW fuel in the tank. This causes any moisture in the fuel/tank to corrode the electric fuel pump. So, you always leave the fuel tank FULL when storing or camping for long periods where the vehicle is not being driven. Auto's have fewer problems because the majority of people drive the Auto regularly and refill the fuel tank regularly. I have a 1975 Corvette with 29,000 miles and ALWAYS leave the fuel tank FULL. I have never had a tank fuel level sensing unit fail(rust/corrosion the most common cause on old vehicles), because any possible moisture cannot get to the sending unit. Doug

D.E.Bishop wrote:
In comparison to my high school years those of us that had 50 or 51, Mercs or Fords and carried an electric pump knowing full well that the mechanical pump was going to fail, the new block mounted and in tank pumps are bullet proof.

Life was not so complex back then. You could fix the fuel pump on a 50 Ford with a chewing gum wrapper.

Since the advent of HP in tank pumps and block mounted pumps working in tandem, I have only replaced two in tank pumps. With my carburetor equipped P30 Bounder with a LP, in tank pump, the engine would run and was drive able abet at a slower speed. The two times that my HP pump failed, nothing, no start, no move.

In comparison to my high school years those of us that had 50 or 51, Mercs or Fords and carried an electric pump knowing full well that the mechanical pump was going to fail, the new block mounted and in tank pumps are bullet proof.

Consider this; some engines are designed for air cooling and have the surface area to transfer waste heat to the surrounding air. Higher power density engines use liquid cooling because the capacity of liquid to transfer heat is higher than gasses.

So if you drain the coolant from a liquid cooled engine and run it with air cooling it's somewhat analogous. No doubt in tank fuel pumps are designed to tolerate a certain amount of that, however it's not ideal to run elevated temps.

In my experience the in tank pumps are more reliable than the engine driven or remote mounted electric pumps ever were.

When the in-tank fuel pump failed on our previous gas coach in Arizona, I picked up a universal inline pump and a spool of wire at NAPA and had us back on the road with about an hours work. Later on when time permitted, I cut an access opening under the bed over the fuel tank and replaced the in-tank pump.

I don't know fuel pumps but I do know large pumps used in HVAC systems. Those large Weinman pumps use the medium being pumped to cool/lubricate the seal between the liquid and the carrier bearings.

pnichols wrote:


I'd pay more for a new RV that included dual in-tank fuel pumps.

By the way, do fuel injected engines actually NEED in-tank fuel pumps ... or could a powerful enough and field-replaceable fuel pump still be mounted right at the engine for them?

A lot of gas engine fuel injected cars have fuel pumps mounted outside the fuel tank when it is nearly impossible to remove the fuel tank without major surgery in a properly equipped shop. Older Bosch fuel injected Mercedes, VWs and Audis come to mind. The pump is usually mounted so that it is gravity fed from the tank so keeping it below the bottom of the tank is helpful but limits its location options.

Chum lee

In interesting thread. After spending a ton of money because of a lift pump failure on our diesel 5.9, I now have a system that if it fails I can just unscrew failed pump and screw in back up pump, but that is diesel.

I've been in the planning stages (and currently stuck on ideas) for a back up system for a small class C. To me gas seems harder than diesel to work out the plumbing and sucking process.

Does anybody know if when a gas pump fails you are able to still suck fuel (with a different pump) that would be hooked up in fuel line?

pnichols wrote:
The main problem with in-tank fuel pumps in RVs is that if you're "way out" somewhere with your RV and that fuel pump fails, it cannot be (well, nearly impossible without access to the top of the tank from inside the RV) replaced in the field ... and even if you can get out with a cell phone ... maybe a tow truck will not come out there to get you at any price. For example, I have in mind many remote and pristine public land boondocking spots in Utah, many of which can be easily reached with a small enough non-expedition Class A/B/C 2WD RV in dry weather... but you better not have an in-tank fuel pump failure when out there.

One can carry along an extra timing belt, one can carry along flat tire changing/repair equipment, one can carry along extra engine fluids, one can carry along jacks, shovels, boards, and a massive tool kit, it's easy and inexpensive to keep engine hoses like new before trips, the engine can run without a working alternator, etc., etc.. But a failed in-tank fuel pump is a different story. In the "old days" one could carry along a spare fuel pump that could actually be installed under the hood while in the field.

The relatively simple OEM solution to this reliability/safety issue is to design in TWO in-tank fuel pumps, with both operating in parallel with each other so that if one fails the other can easily continue supplying fuel. Then compliment the dual fuel pumps with a warning light on the dash indicating that the vehicle is now operating on only one fuel pump if one ever failed.

I'd pay more for a new RV that included dual in-tank fuel pumps.

By the way, do fuel injected engines actually NEED in-tank fuel pumps ... or could a powerful enough and field-replaceable fuel pump still be mounted right at the engine for them?

It might be more practical to either upgrade the fuel tank and isncorporate some way to change the fuel pump in the field, or to add another tank with it’s own pump. My 91 Ford p/u was set up with two tanks that way from the factory.

Pumps in general seem to like pushing a liquid better then pulling the liquid which probably explains why they are in the tank. Better pressure and better volume when you push a liquid.

The main problem with in-tank fuel pumps in RVs is that if you're "way out" somewhere with your RV and that fuel pump fails, it cannot be (well, nearly impossible without access to the top of the tank from inside the RV) replaced in the field ... and even if you can get out with a cell phone ... maybe a tow truck will not come out there to get you at any price. For example, I have in mind many remote and pristine public land boondocking spots in Utah, many of which can be easily reached with a small enough non-expedition Class A/B/C 2WD RV in dry weather... but you better not have an in-tank fuel pump failure when out there.

One can carry along an extra timing belt, one can carry along flat tire changing/repair equipment, one can carry along extra engine fluids, one can carry along jacks, shovels, boards, and a massive tool kit, it's easy and inexpensive to keep engine hoses like new before trips, the engine can run without a working alternator, etc., etc.. But a failed in-tank fuel pump is a different story. In the "old days" one could carry along a spare fuel pump that could actually be installed under the hood while in the field.

The relatively simple OEM solution to this reliability/safety issue is to design in TWO in-tank fuel pumps, with both operating in parallel with each other so that if one fails the other can easily continue supplying fuel. Then compliment the dual fuel pumps with a warning light on the dash indicating that the vehicle is now operating on only one fuel pump if one ever failed.

I'd pay more for a new RV that included dual in-tank fuel pumps.

By the way, do fuel injected engines actually NEED in-tank fuel pumps ... or could a powerful enough and field-replaceable fuel pump still be mounted right at the engine for them?