91 300se. When I stop for gas and take off the gas cap there is a definite vacum in the tank which gets released when I take the cap off. You can hear a whoosh. First, is this normal and secondly if not normal what may be causing it. Thank you for any help. Milt.

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Milterino
76 450 S.E.L.

Completely normal. It means your gas tank vent is working like it should. The vent valve holds 50 Bars+ -. Over 50bars it open and vents into the charcoal canister.

My Euro 500SEC would not pass CA Smog Evaporative Functional Test because the tank would not hold 35 bars. It was the tank vent line hose to the valve that had a hole that could not be found until on a lift.

BTW that valve is found somewhere behind the right rear wheel in the well.

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1986 Euro 500SEC "RUF" 9:1CR, "Rose"
1985 Euro 500SEC Cabriolet AMG Widebody
1982 Euro 500SEL "Blue"
2001 Texas Heeler (Aussie/Queensland X) "Sulphie",
2012 Queensland Red Heeler "Squeak"
Best dogs I've ever had.

Chadahar: Thanks for your information on the vacum. One less thing to bedevil me. Milt.

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Milterino
76 450 S.E.L.

Chadahar, 50 bars would be over 700psi. That's unbelievable, plus you probably wouldn't be able to unscrew the gas cap. How about .5 bar?

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Fred Hoelzle

Yeah, I dropped the decimal it...........yeah that's it.....I just remember the 35 and 50 and all the hoops I had to jump through to get BB smogged a year ago.

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1986 Euro 500SEC "RUF" 9:1CR, "Rose"
1985 Euro 500SEC Cabriolet AMG Widebody
1982 Euro 500SEL "Blue"
2001 Texas Heeler (Aussie/Queensland X) "Sulphie",
2012 Queensland Red Heeler "Squeak"
Best dogs I've ever had.