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Old 02-23-2002, 06:13 PM
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domchang domchang is offline
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Join Date: Sep 2001
Posts: 236
fuel tank overpressured? is this normal?

on my 1987 560SL, took it for a ride with the top down today and noticed for the first time a humming noise coming from rear of car. Once I got home I turned off the engine and could still hear this loud hummnig sound coming from gas tank area.

After looking around for a while, on a hunch, I took the gas cap off and as usual I could hear air under pressure come out of the gas tank...the humming noise immediately cut off at this point! There followed a very very faint buzzing sound that eventually went away as well.

my question is the gas tank supposed to be in an "over pressured" condition? I think I read somewhere in this forum that this is to keep the fuel lines under pressure and not boiling over when the engine is hot.

the car starts fine with the engine either cold or hot. Getting 15.5mpg. I can live with the humming noise if this is normal behavior but would like confirmation of this from y'all.


D. Chang
Network Integration Engineer
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