Myth or True?

[..]

Hey guys,

I often run high concentrations of E85 and inorder to achieve a more accurate mixture I like to run down my tank close to empty - let's say to 20miles left to the tank..

Now by doing this I was told it could potentially lead to fuel pump failure. Is this true? It has been one of those big car myths from ever since I could remember but could never get a straight answer.

Thanks
Durim

[joe86]

The idea is that the more fuel surrounding the electric fuel pump the cooler the electric fuel pump so the longer the life. I believe it even though I have never seen any hard evidence to back this up. I am also interested if any person has done testing on this. On a side note Its good to keep in mind that even though it is usually accurate you can run out of gas even if your car says there is x amount of miles left as this is an estimate. I've seen someone run out of gas on their bmw with it saying 17 miles left.

[litebulb]

Had it happen to me once before, the dash said I had 40 KM left but I ran out of gas and stalled. Out of curiosity, I asked the shop foreman and he said that I probably shorten the life on my HPFP. He also said that you should fill up once you reach 1/4 left on the tank (I use to wait for my low fuel light).

[Esteban]

Originally Posted by litebulb

Had it happen to me once before, the dash said I had 40 KM left but I ran out of gas and stalled. Out of curiosity, I asked the shop foreman and he said that I probably shorten the life on my HPFP. He also said that you should fill up once you reach 1/4 left on the tank (I use to wait for my low fuel light).

Interesting info and nice to know.

[Miko226]

I think it differs by car the sensor could be off in some cars that's for sure. I have run my car several times down under 10 miles even down to 5 miles one time. Although it sketches me out when I have my sensor appears to be very accurate however knock on wood. When I fill up e85 I generally do run down to about 10-15 miles before I mix the fuel however the e85 station is probably less than 100 yards from my house it's very convenient

[ONDEMAND]

Originally Posted by joe86

The idea is that the more fuel surrounding the electric fuel pump the cooler the electric fuel pump so the longer the life. I believe it even though I have never seen any hard evidence to back this up. I am also interested if any person has done testing on this. On a side note Its good to keep in mind that even though it is usually accurate you can run out of gas even if your car says there is x amount of miles left as this is an estimate. I've seen someone run out of gas on their bmw with it saying 17 miles left.

This and in general its not good to run the tank nearly empty due to moisture | humidity in the air that replaces the displacement of fuel being drawn out.. The more air (less fuel) in the tank the more humidity enters the tank. When you park the car over night this humidity can condensate and lead to small amounts of water in the gas tank.

I try to never let the tank get below 1/3-1/2 before I fill up again.

Im sure these tanks are made of materials that will not have issues with a little bit of water (old cars - the tank would literally rust) but the fuel itself and the pump do not like H2o.

[mike@x-ph.com]

Never seen any proof of this.
But in theory it does make sense, so i always make sure to keep the gas tank at a 1/3 minimum.

[..]

Originally Posted by Miko226

I think it differs by car the sensor could be off in some cars that's for sure. I have run my car several times down under 10 miles even down to 5 miles one time. Although it sketches me out when I have my sensor appears to be very accurate however knock on wood. When I fill up e85 I generally do run down to about 10-15 miles before I mix the fuel however the e85 station is probably less than 100 yards from my house it's very convenient

I do the same exact thing and the E85 station is right down the block from me.

[Overpar56]

My wife lets our cars (except my 1er) run down way low. I told her never let the low fuel light come on. My dog listens better...

I've been told by several mechanics never let the fuel get too low because the pump can heat up. Fuel keeps it cooler. One SA at my local Mazda dealer sees a lot of Mazda SUVs driven by soccer moms and they replace a lot of fuel pumps due to low fuel.

I rarely let mine get below 1/2 tank before I fill it.

[MuNkY6913]

I get mine to say --- miles left all the time. Haven't had a problem with a fuel pump yet. Guess I'll be the guinea pig. I like being almost empty before I switch to 60% e85. Don't want the mixture being wrong at 19psi and E85 tune.

[..]

Originally Posted by MuNkY6913

I get mine to say --- miles left all the time. Haven't had a problem with a fuel pump yet. Guess I'll be the guinea pig. I like being almost empty before I switch to 60% e85. Don't want the mixture being wrong at 19psi and E85 tune.

What mixture are you doing? 10/3?

[MuNkY6913]

Originally Posted by DurimOne54

What mixture are you doing? 10/3?

10 E85 / 4 93. Well it usually ends up about 3.8 or so 93.

[..]

Originally Posted by MuNkY6913

10 E85 / 4 93. Well it usually ends up about 3.8 or so 93.

Jesus. You must really run down your tank if you're able to almost get 14 gallons!

[MuNkY6913]

Originally Posted by DurimOne54

Jesus. You must really run down your tank if you're able to almost get 14 gallons!

Like I said. The readout doesn't even read miles any more. Just dashes. Haha.

[edisapimp]

Originally Posted by MuNkY6913

I get mine to say --- miles left all the time. Haven't had a problem with a fuel pump yet. Guess I'll be the guinea pig. I like being almost empty before I switch to 60% e85. Don't want the mixture being wrong at 19psi and E85 tune.

Me too ;x (except without the e85).

I'm just a poor planner when it comes to finding a shell station.

[3002 tii]

I drive to 0 miles left more often than I'd like to admit lol. The next fill up is usually around 13 gallons.

[Dackelone]

Originally Posted by litebulb

Had it happen to me once before, the dash said I had 40 KM left but I ran out of gas and stalled. Out of curiosity, I asked the shop foreman and he said that I probably shorten the life on my HPFP. He also said that you should fill up once you reach 1/4 left on the tank (I use to wait for my low fuel light).

I can't see your HPFP wearing out because of this. It's more likely your LPFP(low pressure fuel pump) in the gas tank could wear out prematurely. Plus our car's don't have a replaceable fuel filter. The fuel filter is part of the LPFP! So I would say not to run your tank bone dry repeatedly.

I do think filling up when you have 1/5 of a tank left is ok. I rarely fill up with the fuel light on.

The reason why you can run a car out of gas even with some miles remaining on the dash - is bc that distance to fuel is an average of your last 15 minutes(I think?) of driving. So if you were driving like an old lady, and then once the light comes on, you drive like a mad man... you could run out of fuel even with some miles left to drive on the BC.

[bigjulzz]

Originally Posted by MuNkY6913

I get mine to say --- miles left all the time. Haven't had a problem with a fuel pump yet. Guess I'll be the guinea pig. I like being almost empty before I switch to 60% e85. Don't want the mixture being wrong at 19psi and E85 tune.

So should I wait until Im almost empty to run e85 for the first time? Recently installed flex fuel wires and installed my dp... Still have a half tank of shell 93 in my car though. (Im new to the whole e85 procedure)

[BEAR-AvHistory]

IIRC you can have warranty issues if you let the car run dry. Based on this expect there is some truth about getting to low on gas. When I ran E85 I refueled a 1/4 tank so the mix was consistent, same with a 93/100 mix.