Gasket: oil filler cap
 

When I removed my oil filler cap yesterday, the gasket plopped out. Which side of the gasket should make contact with the inside of the top of the cap: the flat side, or the side with the beveled edge?

The O ring goes on the oil cap.

Thanks!

No problem, I am always here to help the noobs.

LOL. But actually, let me ask you a dumb question, as it's something I've always wondered about (the gasket in my Cuisinart coffee pot lid did the same thing last year, and it, too, has a beveled, or as you say, O ring side and a flat side):

Why is the O ring on the non-interfacing side of the cap? I would guess, logically, that it would be the "business end" of the gasket that makes contact with the oil filler tube, no? (Or maybe that's what you said and I'm misunderstanding.)

Coincidental that this just came up with me, too.

I didn't have time to change my oil because incredibly busy last two weeks.

I took it to a new place (not chain sh*t place) and when I checked my oil later that day after the change, found the black rubber gasket New Yorker is talking about (same o-ring with one flat side and one beveled side) laying on a horizontal surface of the engine block NEAR the oil filler tube.

I put back on so that the flat side is facing up towards the inside of the yellow oil cap, and the beveled edge is making contact with the oil filler tube.

I put it on as such and am going to go down now and check it at 1:22 am on a Saturday night. LOL.

Your logic agrees with mine - beveled side facing down, contacting the oil filler tube. So now I'm confused again. Anyone know, for sure, how it's supposed to go? (And why?)

I think the beveled edge goes toward the cap. It would be more flat and square on the filler tube side.

FWIW, this was discussed on the Subaru Outback forum:

So the rounded side faces down? Just trying to figure out the right way so I don't develop a large vacuum leak.

Jul 14, 2013 - #7
As 1 Lucky Texan noted, the flat side of the "D" shape goes into the groove in the cap. The "rounded" side faces out of the groove and will contact the surface of the fill tube.

Yep, that's what I was assuming.

Thanks for confirming, bro.

p.s. New Yorker & 9k -I miss and love you guys.

Just as a short status update - My 8 ('05 Sport 6MT) has 124,000miles on original motor, zero rust (in salt/snow belt,driven year round), and rides tight like new.

I must've gotten really lucky because I have zero problems still, and have only done maintenance like oil/filet changes, brake pads, rear diff gear oil change, 4 coolant flushes & refills, air cleaner change-outs, two refills after bleeding calipers on brake fluid, and a few other. Maintenance items + new tires x 3 (not including winter snow tires).

This car has been as reliable as any I've ever owned.