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Fuel Pump Question

I read this in another group, is it correct?

"I'm sure you've all heard about not running your fuel injected cars under a quarter of a tank of gas before. I've always been told its because when the tank is low on gas the build up of dirt, gums etc can get into the fuel lines.

No its not!

The reason they place the electric fuel punp in the gas tank is to help keep it cool. Most fuel pump failures happen in summer. Under a quarter tank of gas lowers the fuel level causing the fuel punp to be in the "air" area where heat builds up and that shortens the life of the pump. Here's part of the article I was reading.

Gas prices are out of sight and many people aren't filling their fuel tanks for obvious reasons.

Whatever the reason, the very expensive consequence is the same.... When you operate your vehicle on a regular basis with the fuel level below a

1/4 tank you run the risk of causing damage to your fuel pump, in many cases, causing it to fail, this is especially in the summer time as the temperatures go up!

Most vehicles today have their fuel pumps located inside the tank and one very important aspect to that, believe it or not, is that it is intended for the fuel in the tank to help keep the pump cool during operation. When the gas level gets to a certain point (around 1/4 tank) and the fuel can't cool it any more, the pump overheats and over time this will cause it to fail".

Obviously an American poster, because I put petrol in my tank...

Reply to
Gordon H
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I suggest you check the facts before replying with nonsense like that. Mike.

Reply to
Mike G

Mike,

Re-read the OP (particularly the first line) and then respond to Gordon H appropriately.

Reply to
Woodworm

He was asking. It's still essentially bollocks though.

Reply to
Duncan Wood

[...]

A family member is notorious for running out of fuel. It's unusual to get in one of his vehicles without the fuel light being on. Over the last 15 years or so, I doubt whether he has ever filled his tank above one quarter.

He's never had a fuel pump fail...

Chris

Reply to
Chris Whelan

You're right. I mistook the second half of the post for the reply to the first half. My apologies to Gordon H. The premise is still factually incorrect though. Mike.

Reply to
Mike G

It could be an American fear, a bit like flat batterys destroying your alternator (although one remanufacturer over her claims "Great your customer has bought an alternator They can fit it and forget it, not quite true, 85% of all alternators fitted to cars with a discharged / flat battery will fail within 30 minutes."" who I'm definitely not buying anything from.

Reply to
Duncan Wood

He's almost certainly never had dirt or gums(!!) clog a fuel pipe or filter either. Unless of course he's been filling up at some very iffy places.

Steve

Reply to
shazzbat

In message , Mike G writes

I didn't reply to anything, I asked a bloody question!

Reply to
Gordon H

In message , Mike G writes

Accepted, my apologies for my reply. ;-)

To clarify, I was surprised to read that fuel pumps are located in the tank. I assume that they are guaranteed spark free? ;-)

Reply to
Gordon H

As was pointed out by Duncan Wood, and a for which I apologised. Mike.

Reply to
Mike G

Many - certainly older EFI systems - circulate the fuel, tapping off only what's needed for the injectors at any point in time. So I'd not clear just how the amount of fuel in the tank matters - assuming the pump isn't allow to run dry. More modern ones may have a fuel pressure sensor which regulates the pump output so it only provides the amount of fuel needed. I believe the latter is more sensitive to the temperature of the fuel in the tank.

But since it's from the US, it can be taken with a large pinch of salt. They have bees to match their 10 gallon bonnets...

Reply to
Dave Plowman (News)

Given they're soaked in fuel they wouldn't catch fire even if they did spark. But they're normally sealed.

Reply to
Duncan Wood

I took a petrol tank off a car that had done 120K miles. Took pump off, looked inside, it was perfectly clean. The fuel pump sock filter was quite mucky though. Cleaning it probably ought to be on a 50-60K mile service schedule.

Reply to
Peter Hill

Utter codshit.

Reply to
Nige

In message , Duncan Wood writes

I'd be more worried for the period when they were out of the fuel and in the fumes above it. :)

Reply to
Gordon H

I don't suggest you try this, but it's almost impossible to start a fire in an unventilated tank, once you get over 8% vapour it won't burn.

Reply to
Duncan Wood

Any mixture of fuel vapour + air WILL burn. It may take more energy to sustain the combustion than it makes. It won't explode. Explosiveness depends on mixture, which depends on vapour pressure, which depends on tank temperature. What temperature does it have to be to bring the saturated (in contact with liquid) fuel vapour pressure down to the explosive limit?

A "dry" tank contains a mix of vapour and air that could have any mixture including explosive mixtures.

It doesn't need the body in contact with fuel, it's full of fuel. Pump motor is on pressure side of pump. The fuel flows though the rotor/stator gap. Commutator runs immersed. All electric pumps for high pressure fuel injection flow more fuel than the engine can use. The excess is returned back to the tank from a fuel pressure regulator on end of injector fuel rail. They also have a internal pressure relief valve.

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So what happens when it runs out? The engine stops, rpm signal to ECU stops, ECU switches the fuel pump relay off, pump stops. Every time it's switched off and on again it will run for 5 secs to prime. That's not enough to damage a fuel pump but it's not enough to prime a system after it's been run empty, it's just to displace any vapour lock in the fuel rail.

If anyone tries to sell you some especially strong magnets to put in the fuel line tell em the car maker has already installed them in the fuel pump.

Reply to
Peter Hill

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