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MG TD TF 1500 - Ethanol gas / Expansion?

Does this new ethanol gas they sell now expand much more than the old fuels?

Topped off my tank before I left for a car show (to where the arrow is aprx 5" from full). The gas expanded in the heat so much that it overflowed out the filler cap and ate the paint off my gas tank. There was a pretty good puddle under the car as well. Looks like a repaint on the tank will be in my future. Bummer.

Temperature was near 90 but I don't recall ever seeing gas expand this much. I am guessing there was aprx 13 gallons in the 15 gallon tank.

David Sheward 55 TF1500 # 7427

OBTW: "Izzy" got a trophy to "remember the day".
Insert subliminal humor here!

David Sheward 55 TF1500 # 7427

No. 13 gallons of gas cannot expand to fill a 15 gallon tank.

What's with that paint? Either you bought gas refined from paint remover or you used latex paint.


Lacquer paint & has been on the car since 2001. I have had spills before, never this! I had "sloshing" issues when cornering and installed a plumping fixture (as others have) in the neck to prevent that. It is 5" long, and I fill tank only to the bottom of that. Only other variable is I normally use Shell Gas, yesterday I stopped at Krogers for fuel. Then drove 25/30 miles to the show. I certainly wouldn't think gas could expand this much...but it did! It dissolved the "seal" for the fixture and weeped under the paint. Seriously considering taking a sample of the gas to have it analyzed. Could this be way too much alcohol content in the gas?
David Sheward 55 TF1500 # 7427

That gas may be contaminated with something other than alcohol. I didn't think alcohol was a solvent for lacquer.
... CR
C.R. Tyrell

I canīt believe either that alcohol will do this to paint.

Same with the expansion - no way it expanded that much. Only way I could imagine is that - if there are no venting holes in the pipe and you filled up above the pipe bottom level - the air around the pipe expanded enough to press the fuel up through the pipe. That seems a physically feasible scenario.

Still does not explain the damage to the paint.

Rgds, Mike
Mike Fritsch

I've seen this happen only on cheaper spray paints. Something is wrong, either with the fuel or with that paint!
Steve Simmons

I think that Mike has the expansion answer. If the if the plumbing tailpiece is a tight fit in the tank filler the heating of the air above the fuel could, IMHO, be enough expand the air enough to force the fuel up and out of the filler. Bud
Bud Krueger

Could your Krogers station be next to a body shop? In some places local to here, where I live, at one time used to dump the waste thinner into the fuel tanks to dispose of it. I hope that is not the case with your fuel issue.
... CR
C.R. Tyrell

Bud's got it... if the anti-slosh neck was a very tight seal. The AIR above the fuel could do that, but not the fuel itself.

The expansion coefficient of gasoline can easily be tested. Fill an old black motor oil bottle within 2 inches of the top and leave it in the sun.


OK...That is starting to make some sense. The tailpiece is lose in the tank, I guess I just got "lucky" (NOT) that it made a really good seal this time. I am still very suspect of the make up of this "gas?". In 14 years I have had gas spills on the paint more than a few times. Never had it do this. There is a small airport using airport transfers sevenoaks near me I may try and take a sample to for an analysis after the holiday. I was out looking at other cars at the show so this happened in the space of less than an hour. Guy next to me in a 48 Kaiser came looking for me as there was about a 1/2 gallon puddle of gas at the rear of the car. Poured water on the tank, dried it with a rage and went in search of some oil dry for the puddle.
David Sheward 55 TF1500 # 7427

Try checking the boiling point of the gasoline by heating over a hot plate in a beaker of water. (there is a good video on u-tube on the subject listed as "boiling point of gasoline").
I did this experiment here in Quebec in the spring with ethanol and hi-test Shell (supposedly ethanol-free). Liquid gasoline began to bubble at 95F (both the ethanol-added and the hi-test Shell) and by 125F the gas was at a rolling boil. If all that gas isn't vented I'd suspect it could blow the gas out any available outlet? (and watch out for smokers!).
The formulation of gasoline is varied significantly by the refineries from winter to summer and the effect of ethanol additions on boiling point seems to be undocumented.
Not hard to understand why vapor lock problems are endemic on old carburetted cars with only 2-4 psi fuel pressure. Underhood temperatures on my wife's black '72 MGB were at least 150F.
T W Moore

Dave, when installation of the 1 1/2" pipe was popular, the instructions were to drill a 1/4" hole through the pipe about 1 or 2 inches from the top. I think this was recommended to allow any expanding fuel to flow back into the tank instead of out from under the filler cap. Does your pipe have this hole in it?
Jim Merz

Jim , I missed that one!
It definitely will have one in it very soon.
David Sheward 55 TF1500 # 7427

Dave: Man, if that happened to me, I'd dry it with a "rage" too !! ;-] By the by, I have had a small patch of paint lifted by (repeated) gas spill at the fuel pump mounting... and we don't have much ethanol in the gas here in Newfoundland. (We pump oil but we don't grow much corn...) -- with sympathy, Peter
Peter Pope

Bummer, sorry about Izzy. Larry
Larry Brown

Just to add to comment but this morning I filled a 5 gallon gas can to within two inches of the outlet pipe connection. I left the can in the sun in anticipation of filling my lawn tractor. By the afternoon in 86 degree weather I uncapped the outlet pipe and about 4 oz. of gas was pushed out presumedly by gas vapors. Once the gas was pushed out and the vapor pressure released the liquid gas level in the can returned to where it was originally filled. Normally I pop open the little air tab on the can but was in a hurry and forgot to do this. But this was a sealed gas can container while your gas tank is vented at the cap. Unless your cap and gasket temporarily sealed the tank until enough vapor pressure built up to push up on the cap and released gas. But this was apparently occurring while the car was running and gas was being consumed. Hard to figure what really happen. FWIW. Tim
Tim Debes

I was pretty much in the state of shock when I started this thread! Having had a little time to think (and some things pointed out by others on here) I believe I have a better perspective now.
What I (think) I have learned:
The 1 1/2" "anti slosh" pipe I installed was "sealed"to the neck with permatex gasket. I did not drill the 1/4" hole as Jim mentioned.
From the heat of the day (car had been sitting, not running for an hour or so)I now believe the "seal" swelled & blocked the vent hole.
As others pointed out, the fumes at the top of the tank must have expanded and forced gas back up through the "pipe" to where the pressure finally "broke through" creating a large enough vent to push an alarming amount of fuel out the cap that somehow got "under" the paint on it's way out.
The primer under the paint is pretty much still in tact.
The paint came off in an "elastic state" ...mostly in one piece.

I guess the only good thing is maybe this thread can save some else from having the same problem? For that reason I am going to include the following in the hope it may be picked up by the search engine at a later time.

Gasoline Damage to paint.

Still not sure if the composition of newer gas formulas was not a contributing factor.

Spell check changed "rag" to "rage"...but it was I left it that way!

David Sheward 55 TF1500 # 7427

I donīt have the hole in the pipe either - but now i know why it should be there...

Rgds, Mike
Mike Fritsch

Mikes comment is the best reason for sharing these kind of experiences on here!
On a positive note: This did give me a chance to review & use my entire vocabulary of cuss words!
David Sheward 55 TF1500 # 7427

I found the info about the hole from an old posting in 2000. Check out "Fuel filler neck pipe". With my memory, or lack thereof, I had to verify my comment before I caused a problem. Golden Years, YEAHHHH.
Jim Merz

Jim. Mempry loss is the second sign of old age.

This thread was discussed between 06/09/2015 and 08/09/2015

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