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Author Message   Jackbequick Posted on Thursday, April 13, 2006 - 10:00 am:        I've noticed that if I run the engine at fast idle with the seat off, pressure builds up in the oil tank on my M2. It is enough pressure that if I tilt the cap and lift a little, there is an audible hiss for a second or so before the pressure bleeds off. My tank is not overfilled now (just barely touching the tip of the dip stick). Is this pressure build up normal? I can see where some pressure build up could be a good thing for the supply side of the pump loop. I'm wondering if that pressure increases with engine speed. And if it is only the presence of the seat that prevents blowing the cap off. In looking at the oil diagram in the SM, it seems that, with the overscavenging oil pump, it is possible that it is returning enough air with the oil to increase the return oil/air volume over the oil being drawn. And I don't see anywhere in the supply and return loop on the oil pump that the pressure would be vented. If all this is normal, I guess what accounts for the cap blowoffs on over fills is that there is not enough compressibility in the air space in the tank to tolerate the normal air pressure buildup. Jack   Blake Posted on Thursday, April 13, 2006 - 01:07 pm:        I dunno, but your analysis seems like it could be valid.   Pammy Posted on Thursday, April 13, 2006 - 02:12 pm:        It sounds normal.   Revperf Posted on Thursday, April 13, 2006 - 02:18 pm:        Yeah. What she said. Pam you are friggin QUICK on the draw girl.   Mikej Posted on Thursday, April 13, 2006 - 02:58 pm:        "Pam you are friggin QUICK on the draw girl." When one rides a 150hp X1, one needs to be quick.   Buellistic Posted on Thursday, April 13, 2006 - 03:14 pm:        Found out when "i" was up in North Carolina in October, if you have the seat off with the stock FILLER CAP,w/dipstick with the egnine cold on an S3, it will blow the FILLER CAP out of the tank and into the air with 20W50 oil in the oil tank ... THAT'S PRESSURE !!!   Blake Posted on Thursday, April 13, 2006 - 03:53 pm:        Thanks Pammy and Brian. Will get you two arguing one of these days. Mike, Dude, that'd be 160 STD RWHP. LaFayette, Get thee an aluminum oil tank and never again worry about blowing your cap.   Jackbequick Posted on Thursday, April 13, 2006 - 03:58 pm:        Thanks all, I feel better about it now. If it quits raining maybe I'll test it on the road tomorrow. Buellistic - There's no doubt in my mind that it can build enough pressure to do that. It popped up into my hand readily, I was a little surprised by it. I guess if you are not overfilled when the cap blows the amount of oil that comes out is not very much. I wonder if there is enough pressure for an air horn. Hmmm... Jack

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