Oil leak

I checked under my car today and found what I believe to be an oil leak. I have no idea how long it’s been like that, I didn’t notice it while changing the oil about 3 weeks ago. when changing the oil, I filled it too fast and some came out and went into the drain hole. I thought maybe the residue I’m seeing could be some of that oil burned onto it. I poured water down the hole to which the puddle of water came out to the right of the oil residue (photo attached), so I think that rules that possibility out, which unfortunately means that it must be a leak somewhere. I filled my oil to the maximum oil level at the time of my oil change 3 weeks ago, and the oil level is now one mark down. I’ve added hopefully enough photos to show where the oil residue is. If anyone has any ideas where this may be coming from please let me know. If I get a chance this weekend then I’ll try get a better look under the car and figure out what the part with the oil on it is.

Had you ever seen this stain before the oil change? If the oil stain is commensurate with the act of the oil change only, then a good washing of the area and monitoring would be my first step. Another indicator would be the cessation of floor staining after a given period of time. Every time I change the oil, I purposely underfill, take short trips and top it off to where I want it to be.

Suggest using some nitrile gloves, or similar, and wipe down the entire area with some brake klean, and the floor beneath the leak. Then I would place a piece of cardboard directly under the engine/trans assembly. Makes it easier to pinpoint the exact location where the leak might be occurring. I had a similar appearance on the underside of my engine and trans from a leaky rear main seal.

Everything Chuck said, with the addition of suggesting you use white paper, just in case you are confused as to what is dripping, it’s much easier to identify fluid colors.

Note that nothing is dripping, the photo with the wet floor was me pouring water down the oil fill overflow tube to see where that comes out.

I didn’t notice this before/during the oil change, but also wasn’t really looking in this area. No fluids have dropped onto the floor. I’ve got a 9 hour drive coming up this weekend, and then will leave it sitting during my 1 week holiday after that. That should be enough to get more oil coming out of the leak after cleaning it to identify where it’s coming from easier.

Hmm, crankcase pressure pushing oil past the rear main seal...failing AOS perhaps?

I had a similar issue, where the underside of the engine/trans was grimy with oil, no drips or puddles either. Turns out it was a leaking rear main seal.

I’ve just gotten back under the car and wiped off all I can easily reach. I will shortly leave on a road trip and report back whether the grime comes back. A friend mentioned it could be CV grease. Does anyone have any thoughts on that? I also noticed that there is a similar grime all over pretty much the entire underside of the car. Considering this is the only part of the underside with no undertray, I think there might be some possibility of it just being wet brake dust and dirt. I guess taking a look after my road trip will tell me.

Am I correct in thinking that if the problem was the rear main seal, then the flywheel would have some kind of oil residue on it? there are gaps underneath the engine that lets me see the flywheel, which looks to be in perfect condition with no fluids anywhere near it.

I wouldn’t guess CV grease would leave that coating, or in that area, but stranger things have happened. Although in my case with the rear main seal, the grimy coating had the same appearance as yours. Keep us posted.

I've had the CV grease "spin" out on my Cayman and it is very localized and evident when you see it; it is also much thicker than oil residue. You can also rule out brake dust as it is always on the outside or barrel of the wheel. I was thinking that was a rear main seal leak.

As others have said, clean it up and monitor it. I assume now you will be checking the oil level on the dash gauge everytime you get in the car so unless something crazy happens, you may just want to have a spare quart in the car that you can add. Something you can do is add dye to the oil and check the area with a blacklight flashlight. The dye and the light can be purchased at any autoparts store. It will tell the story in a hurry. See picture below. Regarding the clutch, as you can see in the pictures below the friction face of the clutch is enough outward that I think it avoids the natural path of the oil from the rear main seal. According to Jake Raby Porsche has come up with an improved rear main seal since these cars were new.

BTW, if you choose to go the dye route, wait until you get back from your trip. Some oil leaks show up very quickly. The one in the picture above showed up within 5 minutes. So you want to be engaged in your engine inspection once you get the dye loaded. Below is a picture of the rear of the engine. There is a largish oil seal around the crankshaft and a smaller one around the IMS bearing cover. Both are candidates for an oil leak. They can be repaired without breaking the engine crankcase apart but it will be required to separate the engine from the transaxle. Also, pull the carpet and top engine cover. You may get lucky and find the oil leak is on the topside of the engine. Again, the dye will show up leaks that the naked eye won't spot right away. Just plan on doing a general scan on the top of the engine. You will probably want to wash the grime away that you will find but even if you don't, new oil coming out with the dye will readily show up.

I found the most likely culprit of the leak while doing a transmission service. On the front half of the transmission pan I was missing one bolt and many around it were loose. There was also an identical residue on the underside of the pan.

Nice job finding the root of the problem. It’s always vexing when one of these issues crops up and leaves you scratching your head. But it’s always satisfying when your investigation and search for an answer ends up with a solution and success at a fix.