Why You Shouldn't Run Your Car Low On Gas

[Gforce]

Originally Posted by why?

That is specifically why most cars are designed now with the idea that the fuel pump be totally submerged until there is very little gas left. The smart ones are designed so that the pump is still submerged when the fuel gauge is telling you it is totally empty.

You might be surprised at how hot that very small amount if fuel can get. Mind you, if the FI system is not a tank return system the fuel tank stays much cooler. Older designs were fuel tank return systems and those could heat the fuel tank fuel up to vapour lock temperatures on hot days if there was not much fuel left.

Refuel just when the low fuel light goes on is good advice.

PS, the fuel pump is only submerged in the fuel it picks up. They sit quite tall, vertically oriented. The fuel pick up is the only part of the fuel pump assembly that is fully submerged. The pump itself draws fuel into the housing around itself which is what cools the pump obviously, that heat accumulates faster if the tank is nearly empty.

Older designs used two pumps: the main pump which hardly ever failed siting in a small chamber that was primed filled and partially pressurized by a small pre pump unit that frequently failed. That pre pump was not always fully submerged draw your own conclusions.

[Sideways]

I have always refueled when my gas light comes on. Our 86 tanks are plastic and fuel pump is mostly plastic or zinc plated steel. And even then, I refuel the same day as the gas light comes on.

I guess it will be bad if you park your car for extended period of time with empty tank or driving in hot weather on empty tank to overheat the pump.

[ZDan]

Originally Posted by Gforce

This advice is correct. In tank fuel pumps are cooled by the fuel in the tank. Frequently running the tank very low can shorten the service life of the fuel pump, especially in hot climates.

As long as the pump is drawing fuel, it is being cooled. So don't run out of gas. But people already know that's a bad idea anyway.

Regarding contaminants and moisture, you're going to have those anyway, whether you run the tank to near-empty or not.

Originally Posted by Gforce

Me too. I had a pump failure on one of my cars and it is pretty inconvenient. Fuel pumps last the life of the car if you don't abuse them.

Running the tank to indicated "empty" (and beyond by some amount) generally does not constitute "abuse". Repeatedly running out of gas would, but nobody wants to do that anyway.

Refuel just when the low fuel light goes on is good advice.

Or when it gets to "E", or whenever you feel like it as long as you don't run out of gas.

People don't need to read an unnecessary alarmist article to know they need to put gas in the tank before they run out...

[Tcoat]

Originally Posted by Gforce

This advice is correct. In tank fuel pumps are cooled by the fuel in the tank. Frequently running the tank very low can shorten the service life of the fuel pump, especially in hot climates.

Any solid contaminants tend to accumulate in the low point of the tank, the fuel pump tends to draw from the low point. For those who think fuel is always free of contaminants ask yourself why all cars fit a fuel filter. Contaminants all pass through the pump on their way to the filter.

Water contaminatation is unavoidable. Fuel floats so guess where the water is. Gasoline contains water absorbing additives, most gas in Canada has lots of ethanol which dissolves water nicely. Shell V power 91 does not have ethanol but does have a water absorber. Water contamination is now rare, but, I still pop a bottle of gas line antifreeze into my cars once or twice a winter. Good preventative maintenance. Isopropyl alcohol versions are more expensive but twice as effective. Most water in fuel is condensation. Obviously the less fuel there is in your tank the more humid air there can be. The less often you refuel the more water there will be in your fuel. Condensation rates are affected by how many temperature cycles the same air volume goes through and how much air is there. In winter in Canada condensation in your fuel tank can be significant, ditto underground tanks although the temperature doesn't vary much at the depth of the storage tanks.

Always buy gas from a reputable retailer.

Ethanol "dissolves" water? Really?


This shit is hilarious in the sheer repetition misconceptions and quasi science.

[Tcoat]

Originally Posted by ZDan

As long as the pump is drawing fuel, it is being cooled. So don't run out of gas. But people already know that's a bad idea anyway.

Regarding contaminants and moisture, you're going to have those anyway, whether you run the tank to near-empty or not.

Running the tank to indicated "empty" (and beyond by some amount) generally does not constitute "abuse". Repeatedly running out of gas would, but nobody wants to do that anyway.



Or when it gets to "E", or whenever you feel like it as long as you don't run out of gas.

People don't need to read an unnecessary alarmist article to know they need to put gas in the tank before they run out...

Here is the reality of this! ^^^^ Low gas means nothing. Empty means possible issues.

[StraightOuttaCanadaEh]

Originally Posted by Tcoat

Ethanol "dissolves" water? Really?


This shit is hilarious in the sheer repetition misconceptions and quasi science.

I think he meant to say miscible.

[Tcoat]

Originally Posted by Sideways

I have always refueled when my gas light comes on. Our 86 tanks are plastic and fuel pump is mostly plastic or zinc plated steel. And even then, I refuel the same day as the gas light comes on.

I guess it will be bad if you park your car for extended period of time with empty tank or driving in hot weather on empty tank to overheat the pump.

And this is reality as well ^^^
I bought a barn find Karmann Ghia that sat with and empty tank for 15 years. Anybody want to guess how much rust or moisture was in the tank?
Nothing!!!!!


How people think that there is enough air movement in and out of a tank to keep building up new moisture is beyond me.


Take a 5 gallon pail.
Cut a small hole in the lid.
Place it outside and let it sit through heat cycles.
See how much water builds up from condensation.
It will probably not even be detectable.


We have huge half full tanks of oil at work that are tested weekly for water. The total found over the course of a year is about 2 quarts. Any amount of condensation in a car fuel tank will be so low it may as well not exist.

[Scrappydoo]

It's not an acorn it's an old chestnut.

[Azzudien]

So let me see if I can sum up this entire thread:

Run out of gas is bad

[Tcoat]

Originally Posted by Azzudien

So let me see if I can sum up this entire thread:

Run out of gas is bad

And running low on gas is not the same as being out of gas.

[Dadhawk]

Originally Posted by Tcoat

Here is the reality of this! ^^^^ Low gas means nothing. Empty means possible issues.

Yep. Here is our fuel pump. You would have to keep your tank well over half full to keep the pump submerged, never mind it's wrapped in plastic and not directly in contact with the fuel. It's the fuel running through the pump that cools/lubricates, not the fuel around it. I suspect the pump would work fine completely outside the tank.

[Tcoat]

Originally Posted by Dadhawk

Yep. Here is our fuel pump. You would have to keep your tank well over half full to keep the pump submerged, never mind it's wrapped in plastic and not directly in contact with the fuel. It's the fuel running through the pump that cools/lubricates, not the fuel around it. I suspect the pump would work fine completely outside the tank.

Not according to some!

[Yoshoobaroo]

Originally Posted by Dadhawk

Yep. Here is our fuel pump. You would have to keep your tank well over half full to keep the pump submerged, never mind it's wrapped in plastic and not directly in contact with the fuel. It's the fuel running through the pump that cools/lubricates, not the fuel around it. I suspect the pump would work fine completely outside the tank.

That's the fuel pump inside its surge tank. That 'bucket' is designed to stay full of fuel even when the tank is very very low, to ensure cooling.


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[ZDan]

Originally Posted by Yoshoobaroo

That's the fuel pump inside its surge tank. That 'bucket' is designed to stay full of fuel even when the tank is very very low, to ensure cooling.

If this ensures that the fuel pump is cooled "even when the tank is very very low", why again should people worry?

B.S. story is B.S. Sure, it's not a good idea to run completely out of fuel, but people already have incentive not to do that!