Ever since we got our GLS 550 a few years ago, it's had a nagging oil leak. When it was still under warranty I took it in and they wanted to do the lower oil pan gasket, but I found that odd considering I could see oil way up above that area. They insisted and so it got replaced but the leak continued.

When I brought it back in a week later to get the rear A/C line replaced, they had to take the transmission down and I suggested they have a look at the rear main seal. It looked perfectly clean in there. Both they and I looked up around the sides of the engine to see if we could figure out where it was coming from, but there wasn't anything obvious. I left and they finished up the a/c line replacement and gave the car back to me.

For what it's worth, I think it only leaks when the engine is running. If it is parked for a while, it doesn't have a slow drip or anything like that.

About a month later I talked to them again about it and they said to bring it in and they'll do more investigating. Here's where it gets a little disappointing. The service manager said they used some dye and traced it down to leaking valve cover gaskets, and he said they replaced them, free of charge (since the oil pan gasket replacement they did didn't work and was around $600). All excited it was finally fixed, I brought it home and didn't really think about it again, until my next oil change.

During the next oil change, I found the same exact amount of oil leakage everywhere, mainly covering the lower oil pan gasket like it was before. After looking at the top side of the engine, it was clear none of it was ever touched, so I was basically lied to. This led to a strongly worded Google review.

I just got done doing another oil change and I really would like to figure this out. I really don't think it's coming from the valve covers (these engines have a pretty complicated design where what is normally a "valve cover gasket" is also what secures the camshafts in the head, it's all one solid piece that gets bolted down, and it is also sealed very well). I was able to get a mirror down there and the undersides of the heads above the exhaust manifolds looked brand new and completely clean all the way around.

So what else could it be? Leaking turbo oil feed or return lines? Has anyone else had this kind of slow leak?

 

We had almost the same odd (slow) drip on ours - recently serviced. We had a seeper at the timing case cover. That said, we had them replace just about every seal in the car.

 

Photos please.

Front cylinder head covers are common leak points on these years.

Leak while running and no drip when stop indicates top half of engine leak. Bottom half is immersed in oil when stopped. Top half is “dry” when stopped and wet when running.

 

Thanks. Yea, multiple techs have tried to track down the source, and I've spent a few hours with a flash light and a few mirrors and been unable to find it. I don't really think it's the timing cover because the whole front half of the engine is surprisingly clean, zero leaks up there.

Photos? Haha, just imagine the whole lower oil pan covered in oil, and what appears to be some coming down from both sides of the back of the engine. Yea, I know that it's gotta be from running, meaning it probably is the head covers, somewhere in the back. The front half of them are easy to look at and the heads below the covers up there are perfectly clean. If head covers leaking is a thing on these engines, then that does help narrow down the search. I think I could take off the intake boxes again and have a better look at the back side of the top of the engine.

 

Clean it off, then try the dye trick again.

 

What engine is that?

I picked up a bottle of UV dye and poured it in the oil hoping to locate some active oil leaks and the stuff was useless in that the oil itself would glow green when a uv flashlight was shined on it. I poured in the dye then next day used the flashlight and everything was glowing green.

 

I would look around with a bore-scope...that said, still sounds like what we had going on...

 

My '17 GLS had a similar leak. Turned out to be the oil filler cap on top of the engine leaking, allowing oil to sneak out under the plastic engine cover.