because doing so will damage your fuel pump.

Been driving for 50 years, even since I turned 16, and only recently did I come across such a nugget. The reasoning is sound. The fuel pump that sits inside the gas tank depends on the gas to keep it cool and lubricated. When the fuel level is too low, the pump is exposed to mostly air, so that puts a lot of stress on it (more heat, more friction) potentially leading to premature breakdown.

Of course, occasionally letting the fuel level dip below a quarter is not going to immediately ruin your fuel pump, but making a habit of doing so more than likely leads to early pump replacement.

I’m the type who almost always runs the tank to near empty before filling up, and I can honestly say that I have never had to replace the fuel pump of all the cars I’ve owned.

So, what does SIGforum’s collective brain say?

I started hearing that a number of years ago, and it seems reasonable to me as well. I've also read that letting the tank get low could cause any sediment in the tank to get stirred up and pumped down the line, which could cause the engine to run poorly.

The only thing I have ever heard of was on some F-150's with the 36 gallon gas tank. The fuel pump was at one end of the tank, and if you parked on a slope in the opposite direction and the tank was not over 1/4 full, it wouldn't start - all the gas was at the other end of the tank.

It depends on the car.

Pump does run cooler, sending unit (gauge) better if under fuel. With the corn syrup fuel, better to keep it fresh.
I rarely let mine get below half a tank, my tank is rather large though in a Silverado.

From personal experience, as someone who drives 40,000 - 50,000 miles a year between work and personal, and who does wrench on cars as well, I am in the “total BS” category (at least for cars made in the last 30-40 years). I tend to fill up when my distance to empty is 5 or so miles (so totally empty), and I have never had even the hint of a fuel pump issue. This is in vehicles with 200k+ miles on them most of the time.

Furthermore, if you take my Tundra for example, it has a 26 gallon tank, yet when totally on E, I can barely get 21 gallons in it. I have read (but not personally verified) that the reason for that is Toyota builds in that reserve for the reasons in the Qs’ post (cooling, sediment, etc.). My theory is this may have not always been true (older cars did not have this built in safety net), so the rumor was born, but it is not true in my experience.

That being said, I do think there are other good reasons to fill up at 1/4 tank (like not running out, etc.), but it is certainly not how I typically operate.

Then again, I also don’t subscribe to the only using “top tier gasoline” theory either, I just put any old slop in my tanks, so perhaps I am not a good example to follow!

It's just old ingrained habit from my first 2 cars being 80s diesels, that would require manually priming the fuel system under the hood if you ran them dry.
I've heard the 'fuel keeps the pump cooler' [for in-tank pumps] but never about keeping it lubricated.

I start getting itchy when I get to about 1/4 tank.
Benefit of being in Houston, you're never more than about a mile from a gas station

It's not BS if you need a safety net, except for a couple years, Toyota pumps rarely fail anyway.

In 'theory 'could' be an issue, but in my experience, it's a verified non-issue. I've had multiple vehicles (4 Volvos since 2004) that all went over 230K miles, and I almost NEVER filled my tank at or above (or even slightly below!) a quarter full. I almost always get gas with less than 50 miles in reserve, and in reality, it's usually less than half that! My experience could be considered brand specific (Volvos are VERY well engineered), but during the '90s I had a Cadillac, a GMC and few company provided Chevrolet vehicles that were either close to, or went over 200K miles as well. I'm known to be that guy that will be driving on fumes...Just ask my wife!

Regarding sediment, I'll call bullshit on that one as well. Your in tank Fuel Pump has a filter sock on the pickup, and there is an inline fuel filter as well. Sediment being 'pumped down the line' is unlikely to ever be an issue unless you have either faulty or poor quality parts. I have NEVER had a fuel issue in ANY of the (modern?) vehicles I mentioned and I've changed exactly one fuel filter during that time, specifically on a 93 GMC back during the '90s. I've NEVER had a Fuel Injector issue in any of that time either, so in ANY vehicle that actually had Fuel Injectors. YMMV

THIS 4.2L 32V V8 Engine however...



I did have to replace both High-Pressure Fuel Pumps on this one. They are located on either side of the engine toward the back, mounted on the Cylinder head(s) adjacent to the Intake Manifold. The in-tank fuel pump however, never had a problem in over 165K miles. For the record, this is also the ONLY vehicle I put fuel injector cleaner in, as it's blessed (cursed?) with Direct Injection. And for that I opt for the highest PEA content available...Red Line SI-1 Complete Fuel System Cleaner.

quote:

Originally posted by Expert308:
I started hearing that a number of years ago, and it seems reasonable to me as well. I've also read that letting the tank get low could cause any sediment in the tank to get stirred up and pumped down the line, which could cause the engine to run poorly.

This is mostly false. The fuel pump always sucks from the bottom of the tank and the tank has baffles to prevent the fuel from sloshing around. I've opened plenty of fuel tanks and have never seen sediment unless the vehicle sat for 12+ months and fuel broke down.

Yes, it is better to keep fuel in it to keep the pump cool.

I'm sure there will be different responses in here. Don't forget location, If you pull into a blacktop parking lot (in July/August) and park in the sun. The fuel and tank vapors are getting rather hot on a empty tank.

quote:

Originally posted by Dzozer:
The only thing I have ever heard of was on some F-150's with the 36 gallon gas tank. The fuel pump was at one end of the tank, and if you parked on a slope in the opposite direction and the tank was not over 1/4 full, it wouldn't start - all the gas was at the other end of the tank.

I have a 2024 and a little bit of an incline on my driveway. I can confirm this is still true.

well back in the day i bought new 1988 chevy truck as long as i was in town driving to work never put more than 5 gallons in it drove till empty , refill another 5 gallons. about 100,000 miles fuel pump went out .I then read about the never let it go empty so i started never letting it get below half way full.when it got around another 100,000 miles that fuel pump went out .it didnt matter what you did .100,000 miles was the built in life of a chevy fuel pump

There's room to play with the quarter-tank figure, but I've had a number of fuel pumps out, and running a submersible fuel pump very low does at least partially expose the pump. The pickup always sits in a tray or recess so that gas can't slosh away from it and momentarily starve it. I think it at least prudent to not let it run that low.

But another good reason to keep at least a quarter tank is in case you have to go somewhere in a hurry without having to stop in a sketchy area to refuel, or stop anywhere, period. A quarter tank can get you 50-100 miles. A weather event, a traffic jam, etc., could require extensive idling. And when I was working, I've lost count of the cars brought in with little or no gas in them. Most cars needed at least a short road test, and some didn't even have enough for that. I was afraid to even drive some of them to the gas station less than half a mile away. On one car I saw the fuel gauge very low, but thought, "OK, I'll take a chance, I'm going less than a half mile." Nope, it ran out. All the time I spent going to gas stations was unpaid. E does not stand for Enough.

This message has been edited. Last edited by: egregore,

This used to be true mainly in high performance cars but a quick search indicates almost all modern cars have the fuel pump in the tank and those need the fuel above, say, 1/8th to help with cooling. Especially in hot weather or when running particularly hard.

I had no idea this was mainstream now.

At the risk of jinxing it, I've largely followed the fill up at quarter-tank advice, and my original fuel pump is still working at 222K. Was it a contributing factor? There's no way to know for certain, of course, but take yes for an answer.

I sometimes listen to a radio DIY call in show for shadetree mechanics. He said in his shop 90 percent of the bad fuel pumps have a full tank of gas. He inferred that pouring the cold gas on a hot pump caused them to fail. I fill up at a quarter tank ever since.

My reason has always been the SHTF theory on gas tank, you never know when or why you need fuel, so at half tank I topped it up. Occasionally I might go to 1/3 but seldom.

quote:

Originally posted by egregore:
At the risk of jinxing it, I've largely followed the fill up at quarter-tank advice, and my original fuel pump is still working at 222K. Was it a contributing factor? There's no way to know for certain, of course, but take yes for an answer.

This has been my MO as well. That is unless we are traveling into remote areas where we either fill up around at around half full or if in worse case scenario whenever we run across a fuel station like the Dalton or remote Eastern Canada in Labrador.

If we have a severe storm forecasted I will fill up the tank just in case like when we lived on the Texas Gulf coast during Hurricane warnings.

I always top off and never let it get to empty, especially on my tuned motors and FI motors. You just never know when you are going to get a bad tank of fuel.