Hi, when changing the ignition coil I've noticed that the back end of the valve cover (right side) is moist from the engine oil. It would look like a valve cover gasket leak, except that the wetness extends both up and down from the gasket, practically to the top of the valve cover. So:
1) Is it the valve cover gasket leak and the oil is pushed up by the blowing air? or
2) Is there some oil hose or some other oil leak source below the intercooler box on the right side top of the engine?
thanks!

 

Look closely and you should see if it’s the valve cover gasket or the turbo oil cooler lines.

If it’s the latter, it’s an awful, engine out, procedure. If it’s the latter, you need to rectify it ASAP before it fries your coil packs.

Good luck.

 

Looks like the valve cover gasket, thanks

 

If you need temporary reprieve, use 2 bottles of Liqui Moly 2020 in the engine oil.

 

It's very minor (no dripping under the car, just some oily dirt on the engine), but I've already bought new valve cover gaskets to change them anyway.

After studying various leak stoppers for a long time I have decided not to use them - yes, they stop the leaks, but also soften all the rubber in the engine which can lead to premature wear of other seals

 

Good call.

 

Is the valve cover gasket replacement pretty simple or a complicated ordeal, I have recently bought a CL600 and after some inspection I think the gaskets are leaking a bit? I'm a fairly good amateur mechanic.

 

It's a little complicated compared to a Chevy V8, but not horrible. You'll need a set of torx sockets. The main issue is that the coil packs have to come off, so if you look for a step-by-step that covers that, that's like 95% of the job. Once the coil packs are off, you need to unplug the cam position sensors and remove the o2 sensor plugs from the holders on the back edge of the valve cover. Then unbolt the valve covers and remove them, you have to slide them forward a little as you lift them so the cam sensors clear.

Since the coil packs are coming off, you'll very likely want to replace the spark plugs and boots while you're there.

I'd estimate 10-12 hours to do it, taking your time and being very careful.

Do you have a STAR system with WIS? At the very least, you'll want all the relevant torque specs.

 

I can't say anything about the CL600. I will say that on the S600, or at least my pre-facelift 2007, there are significant challenges. Pulling the coil packs and valve covers is an exercise in severe frustration that will have you taking German language classes just so that if you ever encounter a Mercedes design engineer you can cuss at them in their native language. There are firewall components, hoses, and cables that make extracting the valve covers a real challenge. As in, take-a-hammer-and-break-it-in-half challenges. For example, once I got the right side cover un-bolted, it refused to clear the rearmost rocker boss. Took me quite some time to coax it out of there, and getting it back in with the new gasket in place was equally time and energy consuming. I did manage to get both sides done, but not in the same day. I was left with the feeling that there has to be an easier way. Like dropping the engine, or using a Sawzall or plasma cutter to open things up a little. Perhaps a dab or two of nitroglycerin would have helped. I'm sure there are easier models. The guy I bought my rebuilt coilpacks from swears he can swap out the driver side pack on his V12 in under 10 minutes. I'd bet $100 he couldn't do that on mine.

 

Yeah, reinstalling the valve covers is kinda finicky. After a couple of tries where I dislodged a gasket, I pulled the gaskets out and tested exactly what motions where necessary to get the covers in place, making mental notes like "OK, start at this position, then lower the cover about 3/4 of an inch, then slide it backwards a bit, then down a little more.........." etc. After I did that it was pretty easy. If you just go straight after it, doing it by feel, you're going to get frustrated.

And yes, the process of actually pulling the coils packs off of the spark plugs takes some effort, but BE PATIENT above all. You don't want to damage them by pulling too hard. Keep in mind that you're basically pulling off 12 spark plug boots simultaneously. Pull steadily and firmly while also gently/slightly wiggling. And prepare yourself for the possibility that you will damage them. Have some $$$ available for replacements, and if it happens, I'd recommend you go to www.v12icpack.com. I don't have direct experience with their stuff, haven't had the need, but from what I've seen I'd go to them rather than buy new.

 

Guess I ought to mention that my SL600 is not my daily driver, so I'm able to approach these things with the mindset of "OK, if it gets too frustrating I can take a break and come back to it tomorrow or whenever" and also "if I run into additional issues and have to wait a few days for parts, that's OK".

I would not want to DIY much of anything beyond very basic stuff on this car if I had to have it back on the road by Monday morning to get to work.

 

Swapping the coils is indeed a pain, and small things get in the way. I would like to see a video of someone claiming that they can do it in under 10 minutes, specially if the coils have been on the car for about 10 years and feel like glued in place.

What helps is to open all the relevant holes plugged by plastics in the bulkhead (the wall at the end of engine bay). For example removing the red insulator from the last spark plug on the right side is practically impossible (if it was left tight on the spark plug after the coil removal) without opening a hole to the battery compartment and reaching from there. Which also helps with the last coil mounting bolt and the actual spark plug removal if needed.

And you want to have all the insulators out and inspected, in case they start getting burnt and need replacement BEFORE misfires prevent the car from being driven

 

I suspect it's a LOT easier on some cars than on others. I know there's a hose going to the brake booster that presents a real challenge on the driver side of mine. On the pax side, I don't remember what exactly was in the way -- may have been an A/C Line or one feeding the low temp circuit. All I know is that it takes every swear word I know (and that's a pretty extensive list, trust me) to get coil packs in and out. The valve covers -- well, let's just say I'm very happy that I'll never have to take them off again.

Ever.

 

Wow, thanks guy's sounds like great advice. Is the removal of the intercoolers easy? I would hope the coolant lines are long enough to just lay them aside.

 

Intercoolers are pretty easy to remove. A few torx socket bolts on each one, worm gear clamps on the charge air hoses, spring clamps on the coolant hoses. Cable-style spring clamp pliers are handy for this.

You should be able to leave the coolant hoses connected and just lay the ICs back towards the firewall, If you do remove them you'll need to use a vacuum-fill method to properly refill with coolant, otherwise you'll have air in the system and this will affect intake air temps. STAR system won't throw a check engine light for high IATs, but it will show a code in the system and it will affect performance. Just an FYI, it is entirely likely that you've already got air in the system anyway, as the stock IC coolant system has no expansion tank - see below about upgrading this.

Of course, the air cleaners have to come off as well. Just a couple of torx bolts each.

Be careful with all plastic vacuum fittings, and electrical plugs - a big twin turbo V12 makes a for lot of heat under the hood, so plastics may be brittle. I cracked the nipple off my MAP sensor and had to order/wait for the new one when I did this job.

If you've got the budget for it, you could consider doing all this at the same time -
Go ahead and remove the intercoolers, and upgrade the IC coolant system by adding an expansion tank. Read through this thread and this thread for two different methods (and the reasons why you would want to do this).

If you've got the IC coolant system open, you're going to have to go through the vacuum-fill process; might as well make sure the entire system is good before you do. Be sure to check the IC coolant pump. It's a common problem for these to go out, and since high IATs don't set off a check engine light you won't definitely know when it's not working. You may notice reduced performance, but that's kind of vague. It's not like the car goes to 0 boost if the IAT is high, it's just reduced, so it's not like the car will be suddenly slower than a Camry. The original pumps are known to be kind of weak, so you may want to go ahead and upgrade to the Bosch "010" pump anyway (Bosch part #0392022010). People have used other pumps (Johnson CM30), but the Bosch 010 is a direct replacement and is entirely adequate within the rest of a stock IC system. The only reason you'd want to go the trouble of a super-high capacity pump is if you're going to exotic stuff, custom-built high-capacity ICs or something.

If you've got a vacuum pump, it's pretty easy to make your own vacuum-fill system. The bleed nipples on the intercoolers are the same size as R410a refrigerant fittings, so I got a cheap set of R410a gauge hoses, a brass tee, some metal bulkhead fittings, and a one gallon air-tight jar to use as a catch can.I think I spent about $40 total on this stuff. And if you don't have one, you can get a workable vacuum pump for no too much $$$, it's not like you need to pull a super-deep vacuum on a large air conditioning system, you just need something that will pull air and coolant though a very small system. I would at the very least get the car hooked up to a STAR system and look for high IAT codes. If there are none, you don't have any air in the IC coolant system and your pump is still working, so you could just leave the IC coolant lines hooked up for your V/C cover gasket job and save the hassle of vacuum-refill. If there is a high IAT code, you either have air in the system, or the pump is out, or both.

Oh, and you DO NOT want to drop any bolt/screws/sockets in the engine compartment! I don't know about S/CL engine compartments, but in my SL there's so little extra room it can really tough to find dropped stuff. I actually bought a USB borescope with a magnet attachment just to be prepared. So just be super careful to not drop anything, nothing makes a job suck more than wasting an hour hunting for a dropped bolt 'cause you don't know if it may have stuck in a spot that would cause problems down the road.......

 

One more thing

When you disconnect the intercoolers from the turbos, you'll likely find that the left side intake path is more oily than the right. This is normal, as the PCV system for this engine feeds into the left side intake only.

 

Indeed, I ordered a dozen or so bolts of various sizes from www.mbpartsource.com just because a few have disappeared down into the guts of the engine bay. Some show up in the under-car splash shields, but some don't. Also -- I'd never seen this before, but locally we have a shop where you can rent a service bay with a lift. The owner has one of those four-finger retriever tools... but this one has a pretty strong magnet on the end as well. WONDERFUL for poking around to find dropped bolts and tools. I'd never seen one before, but I'm buying one now... is one example.

I put my hood in the service position, un-bolt the intercoolers, and use bungee cords to hang them from the hood latches. It keeps them out of the way without needing to open up the intercooler circuit.

If you have a helper, they can hold things (like vacuum or coolant lines) out of the way while you work on getting the coil packs loose and out of there... and the valve covers too.

If you're going to dive in and do this, I would recommend a few things in preparation. Buy the EPC (Electronic Parts Catalog) and learn to use it to find part numbers for your vehicle. My son bought a DVD; it's just a Windows VM image with the EPC on it and cost him something like $20 or so. When (not if) you break something or find something broken or cracked, you can get the correct part number and order a replacement from some place like FCP Euro, Autohausaz, or mbpartsource.com. Do be prepared to replace some parts. There are lots of little rubber and plastic bits attached to that engine, and they do break. I had one of the white plastic vacuum lines split on me... and I discovered that the PTFE tubing used in 1.75mm filament 3D printers (I had some on hand) makes a dandy replacement for some of the vacuum plumbing, and it will be impervious to heat and oil. Dirt cheap on Amazon, and I should never need to replace it again. I've also had a couple little rubber elbows and couplings fall apart, which means they were probably leaking to begin with.

 

This thread will be helpful - it's essentially the same job. Once the coil packs are off, the valve covers are nothing.

V12TT Coil Pack Replacement

 

Thanks so much Bruce, Dale for taking the time. It's great to go into a project with so much information ahead of time!