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Noticed my 2016 981's new oil cap (981-107-035-08) has the same part number as the old cap yet only the new one has the second O-ring. Was the -08 revision silently updated to include that second larger o-ring?
I'm hoping the new cap prevents oil vapor from escaping the filler neck better than the old one I've replaced. It was only a trace amount before, but I consider any an indicator of a poor seal and that's unacceptable.
So far so good but it's only been about a week. However, I think I'm noticing a couple additional benefits of replacing the cap. I can't prove it, but the car appears to have a longer and cleaner cold start idle flare before the RPMs settle down. Further, and I really can't prove this, but wide open throttle pulls appear to be a bit cleaner too. Maybe that's all placebo, but it'll be $30 well-spent if the new cap indeed eliminated all oil blowby.
Old on left, new on right:
To show the share the same part number:
close up of old part number
Some people who were experiencing uneven low-speed acceleration/stumbling found that replacing the oil filler cap made a big improvement. You might be seeing something similar?
You're not wrong, it's been documented that adding an o-ring to the cap has helped the engine run smoother.
Happy to contribute anyway even if I’m late to the party on this item. I found threads about this for the 991 but I think that’s a different part number. Am pleased to know it’s not placebo effect!
Last edited by nicetheory; Oct 30, 2025 at 09:52 PM.
I read an old thread maybe 2 years ago that an o-ring added to oil cap is beneficial. I found that my 2004 Mini Cooper S (R53) oil filter housing rubber o-ring fits perfectly.
I read an old thread maybe 2 years ago that an o-ring added to oil cap is beneficial. I found that my 2004 Mini Cooper S (R53) oil filter housing rubber o-ring fits perfectly.
And probably for a heck of a lot cheaper than the $30 I spent on the new cap. One wonders why Porsche put a nice groove in the cap for an o-ring without actually fitting the o-ring until years later.
Hey what diagnostic software did you use to register the non-Porsche o-ring with your car so it wouldn’t deactivate your spoiler button? Just kidding.
It’s been over a week and so far no oil blowby. I’m calling it good.
All 981 owners, if you haven’t done this yet, do it. All our original caps are probably due to be replaced by now anyway. Just be sure to put a bit of clean oil on your new -08 cap’s fresh o-rings before you install.
I read an old thread maybe 2 years ago that an o-ring added to oil cap is beneficial. I found that my 2004 Mini Cooper S (R53) oil filter housing rubber o-ring fits perfectly.
I just changed the oil and noticed the old o-ring for the oil filter housing also fits perfectly on the oil filler cap. And it was free!
From: On a pygmy pony over by the dental floss bush
I'm holding in my hand a new 981-107-035-08 and yes, it has an o-ring around the upper, larger, diameter of the cap. The OEM one does not. Having said that, I have had zero issues with stumbling at idle or part throttle, or roughness in the engine. Smooth since new. There's a lot of comments here on Rennlist about the new cap restoring smooth engine performance. I can't argue with that, but I never had any such issue with my OEM cap that doesn't have the additional o-ring.
I haven't been aware of any stumbling or power dip with my old cap but when I looked it was very obvious that oil was getting past the lower o-ring. I plan to replace with the newer version for better sealing and if there is a slight performance improvement, all the better. Oil cap after driving ten miles, then resting 15 minutes
So, after reading this thread and the other associated threads, I checked my cap and to my surprise it has no "O" ring at all. I can't say that I've noticed anything odd about my idle speed but, I have a softronics tune. I'll be swapping mine out today just for a piece of mind.....Phil
“If it ain’t broke, don’t fix it” generally holds true but here a little bit of prevention would be good.
I would also suggest wiping the area outside the cap with a cloth to see if it soaks up any oil. If so, your existing cap is allowing that to blow by and it needs to be replaced (or get that 2nd o-ring added somehow).
Last edited by nicetheory; Nov 19, 2025 at 08:16 PM.
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981 oil cap silently updated for a second o-ring?
