Macster

The issue with letting the gas level get real low is the fuel pump is immersed in the fuel and is cooled by the fuel. A real low fuel level means there is little fuel left to absorb the heat from the pump. The pump runs hotter.

A few instances is not sufficient to cause any problems but consistently running around with a low fuel level can over time degrade the fuel pump.

Next with a tank with low fuel there is more sloshing. If there are any contaminants in the fuel -- water mainly -- this agitates the water off of the bottom of the tank where it normall resides and mixes it in the fuel. If this fuel with water gets ingested by the fuel pump it can block the fuel filter (had a truck engine stop like a switch was thrown once when I went around a sharp corner with a low fuel tank and upon inspection found a few drops of water in the inline fuel filter which acted to completely block fuel flow until I removed filter and blew out the water). If it makes it past the fuel filter the water can result in damage to the the injectors and then of course trigger a CEL from a misfire though this will be shortlived.

I would hope the newer Porsches with direct injection systems have fitted a real good water trap to prevent any water from making it past the the 1st fuel pump into the high pressure fuel pump. If not or if it is being overwhelmed and people are driving these cars on a real low fuel tank this might account for some of the fuel pump failures these cars are experiencing. I remember from my time with my diesel powered car high pressure fuel pumps -- be they pumping diesel fuel or gas -- do not like water at all. And the fuel pump on the diesel was a very expensive item. The fuel filter -- just before the pump -- was huge and had a big water trap too. And when I drained it once in a while I always got a few drops of water out of it. So the water does make it up as far as the engine compartment.

When automakers went with in-tank fuel pumps I stopped running gas tank real low except on rare occasions. I generally fill the gas tank when level showing 1/4 tank though I do once in a great while continue to drive to the point the low fuel light comes on.

Most fuel -- just recently too -- I ever put into my Boxster's 16.9 gallon fuel tank was 15.23 gallons. Generally the fill up ranges from 10 gallons to 12 gallons sometimes getting into the 13 gallon figure.

I know -- from my Auto-Xing days -- everyone likes to run low fuel level for the weight savings. Gas weights approx. 7.5 pounds per gallon and a few more gallons of gas is not going to cost you a trophy and might save you some trouble later down the road.

Sincerely,

Macster.

DCP

My car too doesn't play well with most gas nozzles. The upside down technique allows it to work, but so does holding it horizontal. I noticed that some stations now have signs saying not to hold the nozzle upside down and so, to avoid being yelled at, I tried horizontal and it worked.

ROK

It's touch and go for me. My issue is the same as the thread's author (adg). It's not that it's filled up full and the tank reads 3/4 like Pac's. So let's not get that confused. It should almost be a separate post.

I do better with the basic nozzles with no fancy gas fume breather contraption at the end of the nozzle. The kind where you push in so the mouth of the contraption can cover the gas tube on car. The straight nozzle style typically fill up till full.

It's an annoyance that just shouldn't be there in the first place (go Porsche). I don't buy the whole fill up at 1/4 else claim. The manual says nothing about this.

I'll check the fuse.

Edgy01

There was some discussion on this topic a year or two ago. Consensus then was an issue with the filling tube on the 996, and its feedback loop (pressure relief). I understand that these things are not cheap to fix--may require the tank to come out. I just don't buy the tank 1/4 full theory.

robert r

Hmm, I thought i saw something about an inaccurate gauge, didn't register fully the first time...
So trying not to hijack the thread and maybe help someone out I'll try be brief.

The aforementioned audi previously had an issue where the gauge would read half even when full. Solution was:

1. Pull the fuel pump and instrument cluster fuse's
2. Switch the ignition on (without starting the car).
3. Turn off, replace fuse's and start the car.

The gauge then reset itself.

Not a porsche but possibly worth a try?

Pac996

Sounds like something fun to try. I'm pretty sure its a full tank when when its reading below full.

emdog

It's the gas pumps that cause it not to fill completely. I know for sure that Shell pumps do it. I have a gas card for Shell so I have to put gas from Shell and I noticed that it does there. I have had to put gas at other stations, and it did completely fill. What I do is pay attention to how many gallons it should have, then if the pump stops early, I usually top off once or twice, this usually fills it up all the way for me.

JReid

This is what I have resorted to doing as well.

Dennis C

It's easy to get a spill that way though. When it's full, topping it off is bad.

LJpete

Mine never fills up at shell. When I use the upside down method, I seem to get more fuel in the car. It' never quite gets up to the full line regardless of the pumps. Even when I use the upside down, it barely get's there or is just under the full line.

I've never tried topping off as I don't want to have a spill. My average fill up from when the light comes on is around 13.6. Sometimes I'll get as much as 14 gallons in.

Both my first and second 996 do the exact same thing. I figured it's normal.

ivangene

<waving hands in the air>

are you filling with the key in the ignition?

I just wanted to know........

adg44

Yes.

LJpete

No. Key is removed.

ivangene

So I filled mine with the car running a few times and had some issues with the guage and with filling... I then switched to removing the key and either my car fixed itself, or it actually had some effect... I have not had guage issues or filling since????

I run it full to very low ever time too (seldom till the light comes on, but close)

just a thought...... dont know why it would make a diff...

ROK

key has nothing to do with it by my experience. it's the pump style. the more sophisticated it is the more likely it won't top off full. it's tougher nowadays to get the simpler nozzles due to the emissions regulations at the pump level. not that i've ever used arco gas, but those pumps are the worst for the 911. the ones where you have to press in and have it catch before it dumps fuel.