Hello all, I've recently found myself wanting a good summer runabout, and seem to have found a relatively clean 1997 SL600 at a pretty attractive price. When researching these cars however, I keep running into an issue where people will refer to the M120 cars as "more expensive" to upkeep than an SL500 without actually referring to anything specific. Obviously fuel and oil will be more expensive, but if you're worrying about that you really shouldn't be considering a V12 MB in the first place. Now, I should note that I'm no stranger to V12 MB maintenance, being the proud owner of an '04 Designo S600, but with that car the maintenance items that separate it form an S500 are fairly well documented (Coil Packs, ABC, Turbo Seals, etc.). I know that the SL600 comes standard with ADS, but beyond that are there really any common SL600-specifc problems, or is it mostly just people pinning the regular cost of upkeep on an R129 on the fact that it's a V12 instead of a V8. Any advice would be appreciated, the car is seemingly a really good deal, and even if it does need some small issues corrected I think it'd make a great addition to the fleet for infrequent use.

 

I Have a 94 SL320, 98 SL500 and a 99 SL600. I drive the crap outta all 3. Aside from common problems on all three like cost of normal gasket replacement everything else is pretty much the same ADSII is pretty bullet proof as is the engine so if you're DIY and you get a good price on a great running 97 I'd do it. The 97 V12 car is way more reliable than the earlier models in the electrical dept and ADSII at least is not an issue like like pre 06 ABC. How many miles on the car your looking at?

 

The car I'm looking at has ~86,000 miles, and if all goes to plan I should be able top pick it up for less than $7K. The ad mentions a minor oil leak at the front of the car, but doesn't clarify if its an ADS or engine oil leak. I frankly hope its an ADS leak, as I'd almost prefer just getting rid of it and doing the full swap to SL500 running gear.

 

I have a 97 SL600. Have had it about 20 years and do all the maintenance myself. Mine has close to 100k mi now.

You see the key posts/drama going on in this R129 forum. Make sure you get at least BOTH keys AND THEY ACTUALLY WORK! no key = no car

I would say the #1 suspected place to look for oil leaks is the timing cover. I've had to reseal a few M120 engines. The front timing cover upper seals (material) was redesigned at some point. Those original black rubber seals tend to harden and seal poorly over time. If it has the green seal material, they have been changed to the newer material. Oil level sending unit O rings will harden and leak, but dropping the pan is to get at it is somewhat easy. Oil pan can weep if not sealed properly. Valve covers are pretty good usually. I put up with the oil leaks until I had to do the water pump. Those timing cover seals are a pretty big job. But if its leaking badly you don't want a fire hazard either.

ADS II suspension is probably the biggest maintenance weakness on this car.
Listen for any suspension clunking/noise on acceleration, deceleration and going over bumps.
ADS II front accumulators are now difficult to source outside going through the local MBZ dealers here in the US. The rears were somewhat easy, but the fronts, this last time I did them, were impossible to get shipped to me. I believe it's either the size or weight, but after 9-11, they are considered "hazardous materials-Explosives"! I was told, you need some sort of permit to ship them. Maybe some other folks have had better luck getting them shipped . Some ADS small parts are now discontinued, but ebay can be a good source sometimes. Don't even think about buying used accumulators! If they haven't been replaced, the rear steering knuckle bushings will need to be changed and also the rear shocks can loosen over time and clunk over bumps. Tighten those at some point if they are original BOGE units. This car is heavy and can use up suspension, motor mounts and transmission mounts, so keep an eye on those. Bushing rubber will crack too. Consider them consumables.

I personally would not change the suspension system on this car, but can understand why others would. When I purchased my SL550, I purchased one without any form of active suspension.


Make sure the 722.6 transmission's upper 13 pin electrical connector has been replaced or when you get the car, I would just replace it anyways. its cheap and easy to replace. The original ones can weep fluid to the TCU and ruin the harness. As was mentioned by fathertime, the 97's forward wiring harness material was changed and overall have had no outstanding electrical issues.

The SL600 is a fine example of solid teutonic engineering

 

Normally I would be against replacing the active suspension as well, I actively advocate against ditching ABC typically, but I'm buying this as more of a project than anything else, and just don't want to deal with a 3rd car with hydraulic suspension.

So I just got off of a call with the seller, and the car seems like a potential PITA. The car runs well and pulls hard, but seems to be mainly afflicted by electrical gremlins. According to the seller, when the car gets up to temp, it will go slightly above ambient temp and begin throwing codes and putting lights on the dash. I'm no stranger to the complexity of MB electrical systems, so I know that this could very likely be not worth going down the rabbit hole, but my question is this: are there any big picture items that could be causing these seemingly random glitches? The car received a new ECU at a MB dealer within the last year, so it's not that, I just wonder if there could be one unifying issue causing all of the electrical issues.

 

Also, what is access on these engines like? I know on my M275, a lot of maintenance is just a nightmare because it requires partially dropping the subframe. Is the M120 any easier to actually work on, like is an alternator reasonably approachable or would it just be a complete PITA?

 

Alternator is accessible You'll be able to remove it from bottom of car. There is a "decent" amount of room on sides once you remove air filters. I did all my engine mounts without touching subframe. You'll need to pull exhaust downpipes on one side, if I remember right. Starter is a *****. . Timing cover and water pump is tedious work, but accessible from front. You'll need a 3/4 drive breaker bar and torque wrench to R&R harmonic balancer. It's a big tight bolt, as it should be. Can't remember off the top of my head the spec. But my old body couldn't get enough leverage without a 3/4 drive breaker bar. If you're young you may not need it

oh and inspect the harmonic balancer carefully, They have a tendency to crack. They have a hard rubber outer ring. There was a place in LA (CA) that used to rebuild them. Not sure if they still do.

 

You would actually have to know what you were doing (prior specific experience) before buying a less than $7K 97 SL600.

Kinda sorta experience with other MB V12 cars won't get you there.

If I had to guess, I'd say the 2 temp senders at the front of the engine were due to be swapped out.

 

Access for maintenance is not great--a big engine in small frame. The plumbing is a mess if it has not been maintained----lots of hydraulic and coolant hoses--I suggest pulling the hydraulic hoses and take to good hydraulic shop to have them remake them all--keeping proper orientation. this will save you hundreds and lots of issues over time.
For whatever reason, German hoses are all crap

 

The M120 is a piece of cake against the M275, I own both. Sometimes you need a little extra time to do something, but there is nothing to be afraid of. The ADS 2 is not complicated, nothing compares to the ABC.

The only mysterious thing for me is the seal from the oil level sensor. @crconsulting how do you get space to pull the sensor out of the hole?

 

@ AndreasHannover. It doesn’t pull, it pushes.
There’s a clip on the outside. It sits in a counter bore on the outside of the block. There’s also a slot machined into the counter bore so you can push the clip upwards thru that "gate", and release it. You will have to push the clip upwards with a screwdriver or something long. (working from bottom)
Once you have the pan dropped, the sensor comes out from the INSIDE. It has two bolts that I red loctited into place. It helps to slightly lube the O-ring to push the sensor in place. The square end of the sensor seats in place inside the block. Pay close attention to how the wire is routed, and orientation. There is a plastic clip suspending the wire, be gentle pushing the new one back in place. Once it’s seated properly, you push the clip back on, though the “slotted gate”, and rotate it back into place.

Hope that helps, it’s actually not that hard of a job.

Good Luck.


9

 

My fault, i should ask more precise. There is a thread here with a picture inside the engine: https://mbworld.org/forums/sl-class-...er-sensor.html

Some people and i can not pull the sensor inside because of a support blocking the sensor. How do you manage this? Any hints would be very welcome.

 

Thats interesting, Mine is notched. It IS original I can guarantee that too.
Here's the pic I took before I changed out the sensor. (very clean for close to 100k)
Take a look at my rear baffle, its a little out of focus, but you can still see it.
Maybe they changed it starting 98? Lower casting appears different too.

 

Andreas,

My independent tech says there is a special MB tool that he uses to fish the old sensor out and put the new one in.

The oil level sensor is the leakiest part of the engine. I'm on my 3rd one and they never really seem to seal properly. I even got a new outer clip because the original one was a little misshapened over the years.

 

For me, there is no way to get the plug out of its hole. Meanwhile, i think the special tool is a hammer to bend the rear baffle.

 

Agree

 

It looks like that part (65) unbolts no? Unfortunately mines buttoned up or I’d have a look, but I thought I saw some bolts back there.
At least on the ‘97 version of the engine I have. Your casting is definitely different too. Have a look at the illustration below.

65 A1201860195 REINFORCEMENT 001

 

We have two SL600, both year 97. The picture of me was borrowed from the other post.There must be a little secret how to reach the bolts, for me, there is no way to reach them. But your picture shows me, it must be possible. You unbold the oil pan, unbold nothing else only pull it out, magic.

 

On mine I didn’t even unbolt anything! As you can plainly see from my pic, it has plenty of clearance just to remove the sensor without unbolting anything else.
One would expect revisions from factory to IMPROVE the design not make it worse 😕

Just FYI my car was built 10/30/96. When were yours built?
also I worked on a 96 several years ago, doing the same job, and don’t remember having any issues removing the sensor.

I thought you might be able to access the reinforcement plate/rear baffle bolts thru the squarish casting part on the back of the oil pan, but looks like that piece is solid, WTF? You can see from my pic those bolts are right on top of that piece/shelf
Wonder if they forgot to put a hole in that casting??? Doesn’t seem to do anything....

LOL!! 😀 I think the “factory special tool” is a 1” drill bit....

 

12/20/96 and 02/13/97

I will give this thing a second try, maybe it is enough by cutting the edge of the plug..




At the moment, i glued the plug from outside. No one see it, but i know it. Katastrophe.

 

I am afraid that i found the solution, it is a failure by design. This can not work, one screw is behind the scenes, follow the green arrow:



more close


moooore close




And then, an other supplier made an offer, Mercedes could not resist: We make it cheaper.



F**k

 

That is crazy! So we're seeing NEWER M120's revision are the ones that seem to be a problem? late 97-up? (my car was mfg'rd 10/30/1996) It also seems like the upper oil pan casting is different too.
Honestly, don't know how you're going to get at that. That is a huge f**king fail.
Same fool probably designed the blower motor strap

 

12/20/96 and 02/13/97

Now i am curious about the @mahunt special tool

"My independent tech says there is a special MB tool that he uses to fish the old sensor out and put the new one in."

 

I am due for an oil change, maybe I could ask about the oil level sensor tool.

 

That would be nice, but woe, he'll show you a joint ratchet