Low Fuel Tank = Lean?

STIKC · Mar 19, 2013

Just curious. My buddy who drives a older gen STI told me that on all Subaru's the gas lines from the tank are in the front and to never let you fuel level to go below 1/4 a tank. If I do when I floor it all the gas with flow back (duh) and allow it to not go down the lines causing to run very lean and possibly damage the engine. Is this true? If it is true, did they fix this for the newest gen (2013)?

Grinder34 · Mar 19, 2013

what? I dont understand why 1/4 tank would make a difference if fuel were somehow going to flow backwards?

The fuel lines are pressurized by the fuel pump. Acceleration/gravity shouldn't affect the flow.

Batmobile_Engage · Mar 19, 2013

What your friend is saying is a little bit true. Fuel can slosh towards the back of the tank (but is never going to run backwards
in the fuel lines) and the fuel pump can momentarily get starved for fuel, but you'd have to have almost no fuel in the tank for this
to happen. Hell, I've made runs at the track with only a 1/4 tank of fuel for weight savings. lol ;-)

finallymysti · Mar 19, 2013

I can tell u from experience. U can and will starve the fuel pump on track with the needle between 1/4 and 1/2 full (or empty depends how u look at it. Lol). It's happened to me twice. Once was going thru the eases at Watkins glen, and the other was coming out of the lightbulb at njmp. For normal driving and standard hard acceleration u shoul be fine with 1/4 tank.

Batmobile_Engage · Mar 19, 2013

^ Oh shit, really? Maybe I shouldn't do that anymore.

finallymysti · Mar 19, 2013

yes really. now I never go on track without a full tank.

finallymysti · Mar 19, 2013

for 1/4 mile runs you should be fine with 1/2 tank. when i'm on track i'll go thru nearly half a tank in one session. so I need to keep it topped off to be ok

Batmobile_Engage · Mar 19, 2013

Another thing, since we're on the subject. I've seen a guy burn out his fuel pump by
trying to crank the ignition again and again and again and again with barely a drop of
fuel in his tank. I'm guessing it was sucking air, overheated and burned up inside.

Grinder34 · Mar 19, 2013

The only time i fuel starved my car was with the low-fuel light on in a hard left-hander at the track. I'm quite surprised that you managed to do it at ~1/3 tank...really surprised!

But to answer the OP question:
Yes, fuel will slosh and can/does cause fuel starvation
It's not caused by the lines, but the tank
It's a problem on pretty much every car (not just STIs)
I think the ECU detects the loss of fuel and will protect the engine (I'd like verification on that)

Batmobile_Engage · Mar 19, 2013

I don't ever plan on replacing my fuel tank. However, if I was forced to, due to damage or something,
I would try to find one with baffle plates inside (some performance oil pans have the same design) to
reduce sloshing.

Spamby · Mar 19, 2013

Not possible with that amount of fuel in the tank unless your car is upside down. LOL. Probably something else.
The amount of fuel in the tank, the configuration and baffling/channeling of the tank, where the fuel pump depth sits in the tank, where the fuel pump is positioned in the tank. Lateral load/ g-forces and time it would take to make the fuel slosh completely to one side, completely uncover the pump, hold the fuel to the side for a long enough duration to clear any fuel left in the pump, and fuel lines etc etc.

Batmobile_Engage · Mar 19, 2013

^ That's kind of what I thought. That you'd need to have VERY LITTLE fuel in the tank before you'd see this issue.
Either way...a couple of the guys here have made me paranoid, so instead of learning the hard way, I'm going to keep
the tank at least 1/2 full at the track.

Grinder34 · Mar 19, 2013

I burn about 1/2 tank per HPDE session. Its best to just keep a full tank unless you're going for time and every second matters!

Batmobile_Engage · Mar 19, 2013

I was on a verrrry short track... Nonetheless, my Cobb AP (before the race it showed 17.9mpg) reported about 6 mpg. lol

finallymysti · Mar 19, 2013

Spamby said:
Not possible with that amount of fuel in the tank unless your car is upside down. LOL. Probably something else.
The amount of fuel in the tank, the configuration and baffling/channeling of the tank, where the fuel pump depth sits in the tank, where the fuel pump is positioned in the tank. Lateral load/ g-forces and time it would take to make the fuel slosh completely to one side, completely uncover the pump, hold the fuel to the side for a long enough duration to clear any fuel left in the pump, and fuel lines etc etc.

in theory, theory and practice are the same. in practice, theory and practice aren't the same. I have a friend that has an 05 sti and is an instructor with nasa and has had the same thing happen at that amount of fuel.

HolyCrapItsFast · Mar 19, 2013

This happens less on the GR. The tank is a drastically different design and the pump assembly is located more center of the car. The pump assembly is also encased in a plastic housing which acts as a kind of surge tank if you will. You should almost never run into this situation in a GR. The GD was more susceptible to lateral acceleration and fuel starvation while turning. I can't say that I ever ran into this situation during linear acceleration though.

Grinder34 · Mar 19, 2013

the GD has a "surge tank" like thing too, right?

Batmobile_Engage · Mar 19, 2013

Uhhh...?! I don't remember my GD having that... Maybe I'm wrong though, it's been quite a while since I replaced the fuel pump.

Grinder34 · Mar 19, 2013

Might vary by model year.

Here's the pic from my fuel pump install (obviously its not focusing on the surge "tank") but its not just a stock photo:

STIKC · Mar 19, 2013

I think what he was trying to say was at 1/4 tank or lower during hard acceleration fuel is "sloshed" away from where the fuel enters the lines to go to the engine causing starvation which could lead to a oh no situation. He was telling me every time the car gets to 1/4 a tank I should fuel up. He has a 04-05 STI. I was hoping this wasn't something I really had to do.

I appreciate all the replies!

Low Fuel Tank = Lean?

New member

Track Monkey

Squirrel Meat Aficionado.

New member

Squirrel Meat Aficionado.

New member

New member

Squirrel Meat Aficionado.

Track Monkey

Squirrel Meat Aficionado.

Meat Product Toy

Squirrel Meat Aficionado.

Track Monkey

Squirrel Meat Aficionado.

New member

Drinks beer!

Track Monkey

Squirrel Meat Aficionado.

Track Monkey

New member

Similar threads