Why does my car seem to run better with a full tank?

Tishabet · 11-19-2009, 01:37 PM

After years of telling myself I'm imagining things, I've finally concluded that my car really and truly runs better/smoother when I have a full tank of gas. The thing is, I can't figure out what difference it should make... but idle in particular is smoother if I've just topped off. Any thoughts or similar experiences?

mistertate · mistertate's Garage

The fuel pump is at the bottom of the tank. There's more pressure at the bottom of a 20,000 league ocean than a 1 league ocean. Maybe there's something restricting fuel pressure? A fuel filter maybe?

krystar · 11-19-2009, 02:40 PM

placebo effect?

is it the full tank? or the act of refuelling?

what if u just filled up 1/4 tank?

Tishabet · 11-19-2009, 02:56 PM

Quote:

Originally Posted by krystar

placebo effect?

I chocked it up to placebo effect for the last 5 years, but recently I've had a heat shield that has started rattling underneath the car a bit at idle. I've noted that the car doesn't just "feel" smoother at idle (which I would have figured was placebo) but that when the tank has just been filled, the heat shield rattles much less.

I suppose you could say the car is sitting lower on the suspension and the vibrations are lessened by the extra mass of the gas to absorb it.... but it really does feel like it is running better.

krystar · 11-19-2009, 03:38 PM

maybe something to do with tank vent pressure? what if u just open up the gas cap and vent it? any diff?

John_AZ · 11-19-2009, 03:52 PM

More fuel getting past the fuel screen in the tank?

Mine had cuts, straw, bugs, tank slime on the screen

GL
John_AZ

wild man · 11-19-2009, 04:01 PM

Try checking the FPR and the damper diaphragms. Pull the vac lines off and see if you can smell fuel in them.

running_cold924 · running_cold924's Garage

more weight in the ass end=more grip for the rear wheels!!! may just be smoother on the powerband.

ike229 · 11-19-2009, 05:16 PM

Ive always felt this way too.. Both in my 924S, and motorcycle.

Always feels good to fuel up.

legion · 11-19-2009, 06:41 PM

Quote:

Originally Posted by mistertate

The fuel pump is at the bottom of the tank. There's more pressure at the bottom of a 20,000 league ocean than a 1 league ocean. Maybe there's something restricting fuel pressure? A fuel filter maybe?

A league is a measure of distance. A fathom is a measure of depth.

Lapponia · 11-20-2009, 04:16 AM

+1 John Tate and John_Z. Did you look at the FP filter in my thread "Death of a fuel Pump"? There you can see 25 yrs of filter duty but only if you crack open the pump e.g. destroying it. FP is bad all the same and should be exchanged. I guess what John T said about pressure on ocean bottom, sure there is a bit more pressure out of fuel tank when full (pillar height of fuel in tank times fuel density). I would reccomend you to change your FP if 20++ yrs. car will run so much better.
Good luck. Lapponia