refill at 1/4 tank to prevent fuel burning?

[allenying]

hi, back before the internet, I would hear that is best to refill on gasoline at a quarter tank, because when the tank is low it's more likely for fuel to burn, which is not so great for the car and fuel filters.

is this still the case for diesel? or for a W123?

I never had a reason to question it, and just refilled at 1/4 for years, but the reason I'm curious now is because I am traveling 30min to buy B99 biodiesel every 2 wks, but could maybe stretch it to 3 weeks if there's no issue with running lower on the tank.

I saw the specs for my fuel tank are about 21 gallons, and I think about 7 gallons for reserve? when I am at a quarter tank and refill it gets fill at about 13.5 gallons.

thanks!

[pgringo]

The reason it's important to keep at least a quarter tank in a gas car is because the fuel pump is cooled by the gasoline and if the fuel is run low the life of the in_tank pump will be drastically shortened. This doesn't apply to diesels with gravity_feed_to_lift_pump setup.

Edit: of course the in_tank setup may have all changed now with in_tank bladders and stuff like that on newer cars with all this drive-by-wire stuff.

Sent from my MB886 using Tapatalk

[mannys9130]

^ yep.

Gas cars use the liquid gasoline to cool the fuel pump. Liquid gasoline is not flamable. Once you get to 1/4 tank the pump isn't covered well and it lacks lubrication and cooling.

Your fuel pump is mounted to the side of your injection pump. You can go below 1/4 tank but your risk of fuel starvation increases because the lower most part of the fuel strainer might be covered in slime and unable to flow. That probably is not the case if you run B99.

The fuel in the tank won't "burn" no matter what... I think you must be leaving "the fuel pump" out of your sentence.

[allenying]

aha interesting. i didn't used to be interested enough to research why fill at 1/4, it was easy enough and a good habit to avoid completely running out of gas. if there were times i didn't notice going below 1/4, there could've easily been times i'd not notice going below E.

so, i guess if running B99, going below 1/4 on a regular basis should be no problem? i'll give it a try.

[Diesel911]

Originally Posted by allenying

hi, back before the internet, I would hear that is best to refill on gasoline at a quarter tank, because when the tank is low it's more likely for fuel to burn, which is not so great for the car and fuel filters.

is this still the case for diesel? or for a W123?

I never had a reason to question it, and just refilled at 1/4 for years, but the reason I'm curious now is because I am traveling 30min to buy B99 biodiesel every 2 wks, but could maybe stretch it to 3 weeks if there's no issue with running lower on the tank.

I saw the specs for my fuel tank are about 21 gallons, and I think about 7 gallons for reserve? when I am at a quarter tank and refill it gets fill at about 13.5 gallons.

thanks!

Not read or had someone tell me that concerning any Diesel Engine in my 18 Years ad a Diesel Mechanic.

I know I tell my Wife not to get below 1/4 Tank on any of our vehicles because I don't want her stuck on the Road out of Fuel someplace.

I follow that same advice and especially with my 2 Diesel Cars as I don't want to run out of Fuel and end up going through the Air bleeding procedures on the side of the Road or even at Home if I can avoid it.

[vstech]

there are several reasons to keep a diesel tank full...

the big one is moisture.

water will destroy the injection pump in a diesel. also, the fuel filter will rust out and leak if it collects much water in it.

when you leave the tank low on a diesel vehicle, there is a lot of air in the tank. air has water in it, and overnight the water condenses and over time, it will collect and rust the tank, and gunk up the fuel, and damage things.

the reserve should be 3 gallons, if you are on a long trip, it's safe to run low, but if you drive short trips, letting the tank sit overnight with low volume is bad.

bacteria wil grow in the water, and consume portions of the fuel, leaving black residue that will clog filters, and the fuel system itself...

[babymog]

I've never heard any of this "burn the fuel pump", and believe that it's bull. I've run all of my (German) cars from full to reserve tank after tank, some for hundreds of thousands of miles, in-tank or external. As long as you don't habitually leave it low, or leave it for extended periods low (see condensation note above), it will be fine. The pump (whether internal or external) is cooled by the fuel pumping through it, not around it, and in most cases it pumps many gallons/hour which will be close to ambient / outside temp due to the surface area of the tank and fuel lines.

Running it out of fuel is bad, as these electric pumps are lubricated by and cooled by the fuel they pump and running out just once can cause a lot more wear than normal use.

Our older mechanical pump diesels don't care at all as long as all is in good shape and it doesn't sit through hot/cold changes that can cause condensation inside the tank. The only departure from that is the fuel level relative to any leaks that you might have between the fuel pump and the tank, I know of a couple of people who need to park their cars pointing downhill when the tank is low so that a leak in the lift pump or other won't let the fuel retreat to the tank and the car not start.

[mannys9130]

Originally Posted by babymog

I've never heard any of this "burn the fuel pump", and believe that it's bull. I've run all of my (German) cars from full to reserve tank after tank, some for hundreds of thousands of miles, in-tank or external. As long as you don't habitually leave it low, or leave it for extended periods low (see condensation note above), it will be fine. The pump (whether internal or external) is cooled by the fuel pumping through it, not around it, and in most cases it pumps many gallons/hour which will be close to ambient / outside temp due to the surface area of the tank and fuel lines.

Running it out of fuel is bad, as these electric pumps are lubricated by and cooled by the fuel they pump and running out just once can cause a lot more wear than normal use.

Our older mechanical pump diesels don't care at all as long as all is in good shape and it doesn't sit through hot/cold changes that can cause condensation inside the tank. The only departure from that is the fuel level relative to any leaks that you might have between the fuel pump and the tank, I know of a couple of people who need to park their cars pointing downhill when the tank is low so that a leak in the lift pump or other won't let the fuel retreat to the tank and the car not start.

It's definitely real. Modern gasoline fuel pumps need the liquid gas around them to cool and lubricate. Pumping it isn't enough.

My mother had a 2002 Grand Prix 3.1. She's the type that constantly drives around with no gas. Her fuel pump died suddenly (at a gas station, how ironic) at 80k miles.

1/4 tank is enough to keep the pump covered and allow it to last longer.

[babymog]

Our 2nd E150 in-tank pump died at around the same mileage (50k-60k, out of warranty), with a full tank. I always kept it above 1/2.

Maybe Detroit just buys crappy pumps?

I can ask Daimler Engineers next time I talk to them (tomorrow), but it is my expectation that if I present this to them (can't run the tanks below 1/4 or it'll burn up the pump) that they'll laugh, much like they do with other internet legends.

I know many many people who have run cars out of fuel, it typically isn't disclosed when they trade them in. These same people are the ones who always run the tanks low, and put in $10 when it's hovering around the E (or below), chances are good that these pumps have sucked air at some point.