2017 GLS550 148k Service

[rpaoness]

Standard oil change, filter.

Noted a significant oil leak formed above the drivers side down pipe flange. At first I thought the turbo seal had blown and oil was leaking out of the exhaust, but on closer inspection I think its leaking from somewhere around the top of the drivers side cylinder head/valve cover area. Couldn't see well. I wonder what are common leak points there I should go after. Hopefully it doesn't get significantly worse before my next oil change. Wasn't dripping onto or off of the underbelly cover, so i guess it isn't that bad yet.

- Both cover hold down tabs on the engine compartment fuse cover broke off the fuse box base. Zip tied around to keep the cover on and dirt out, but that kinda sucks.
- Need to order a couple of steel spring clips for the center plastic cover on the engine - there are so few I should've left it off already. Not sure how to find the PN.
- Some belt accessory noise starting. Need to order the top center idler pulley and maybe the upper left one. Others felt OK.

Help me out with part numbers for at least the last two when you have a chance.

[rpaoness]

Looks like the clips are:
003-991-51-70 - $8.50 each

The catalog is awful for belt and tensioner listings.

[rpaoness]

I think the top one is this one - certainly inexpensive enough on FCP Euro:
https://www.fcpeuro.com/products/merced ... 6112340293

[kevm14]

The online catalog isn't good in general. I use my offline copy of EPC (electronic parts catalog).

[rpaoness]

I wonder if I should just get all of these.

[kevm14]

I would recommend:
- making sure those are correct. I didn't read the description but I don't really trust FCP euro's catalog either and you can't go by visual
- price out OEM
- Replace all of them unless one is really expensive and that one also feels totally fine. It should feel smooth and make zero noise when to fling it by hand.
- I wouldn't bother replacing the tensioner pulley by itself. I'd either leave it if it's fine or replace the entire thing including the pulley.

[rpaoness]

This isn't any rush, just I usually completely forget about these kinds of things until the next oil change, and if they're there in a box I put them on.

Post PN's whenever you have a chance and I'll correlate w/ RockAuto, FCP Euro or whatever and Benz OEM comp shop. This looked like all of them except the tensioner.

The tensioner looks hard to get to and felt fine, so I'm inclined to run it. The top large dia one is the only noisy/bad one, just figured I'd do the rest just 'cause.

[kevm14]

Noted a significant oil leak formed above the drivers side down pipe flange. At first I thought the turbo seal had blown and oil was leaking out of the exhaust, but on closer inspection I think its leaking from somewhere around the top of the drivers side cylinder head/valve cover area. Couldn't see well. I wonder what are common leak points there I should go after. Hopefully it doesn't get significantly worse before my next oil change. Wasn't dripping onto or off of the underbelly cover, so i guess it isn't that bad yet.

So the most common leak point would be the covers that the cam adjuster magnets (Mercedes speak) are attached to. You might refer to them as front cylinder head access covers (or are they on the timing cover?). Anyway the RTV eventually leaks on these. The covers may be magnesium which has enough porosity that this is an issue over time (this general issue is seen across previous Mercedes engines).

The fix is to remove and reseal the cover. If the cam adjuster magnets are leaking into the harness or their O-rings are leaking (which is also fairly common) it's good practice to replace them while you're in there. You can replace them later but often there are bolt access issues that you will probably resolve while you are pulling the covers so it does make sense as a while-you're-in-there, even though the price x 4 will be in the hundreds. At your mileage you should not feel bad about doing that.

[rpaoness]

Sorry - it was late when I typed that. If it's a valve-cover-ish area leak it's definitely at the back and really hard to see at the firewall. I need to pull more apart to see where it's coming from. It was dripping down onto the turbo exhaust/cat flange and made it look soaked, which makes me think it's a relatively bad leak, even though I didn't notice it in oil level... I was thinking maybe something to do with the centrifuge?

[kevm14]

Oh, rear. That's different.

Most common would be centrifuge cover (pass side) and there are two other rear cam inspection covers that are plastic and just snap on. Also take a look at the vacuum pump (driver's side). If the centrifuge cover and cam covers are original they are overdue.