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Discussion Starter #1
Why sometimes when I remove the gas cap after a short drive ,there will be a release of pressure? Other times after driving for a while ,remove the gas cap and no pressure release at all. any ideas why the difference. Car is a 74 450 sl.
 

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Outstanding Contributor , Bob's Your Uncle!
-----'83 280 SL----- 5 speed....The PIG
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29,196 Posts
Gas sloshing around creates pressure. The less gas in the tank, the more pressure seems to build. The SL tank has a pressure release doohickey that, in first generation, would release the pressure to atmosphere..
Second generation releases it to a hard line that ends at the charcoal canister.
 

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1987 560SL
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3,524 Posts
I'll go out on a limb here and say that you possible have bad check valves at the fuel pump allowing pressure to build back into the tank...it happens to mine at times. A fellow MB owner that also owns an import parts house here in town suggested that I replace mine. He sells them for something like $20 a piece.
 

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1978 280slc
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3,198 Posts
They put a non-vented gas cap on your car allowing the pressure in the tank to build up and release pressure when you open up the gas cap. I failed smog once for not having the non-vented gas cap so that is the deal. A guy with a 380sl euro behind me showed me the difference and 1/4 a gallon of gas came out of his tank, kind of funny.
 
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