'95 S600 V12 Motor Reliability - Mercedes-Benz Forum

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Old 06-27-2011, 11:55 AM   #1 (permalink)
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Date registered: Aug 2008
Vehicle: '95 S600 140.057, '77 300D 123.130
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'95 S600 V12 Motor Reliability

probably should have asked this question before i purchased, but what is the historical record for these engines as far as reliability/durability?

what are the typical problems that can crop up? besides oil/filter changes what else should be replaced/adjusted on a scheduled bases such as valve adjustments, fuel injector cleaning, etc??

thanks,
rick
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Old 06-27-2011, 02:32 PM   #2 (permalink)
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Between my mother and myself, we have six V12 W140's and R129s. They are very reliable if you treat them properly and stay ahead on maintenance. You've got the middle model--which I like much better than the '96+ 140s--that can have wiring issues. Have the top engine harness replaced. I've got a source for them at a reasonable $750. From the stealership they aren't too much more.

The suspension is one of the worst systems on your car from a cost perspective. It's right about $4k in parts to replace shocks and springs. Front shocks are almost $1k and rears are about $700. A cheaper solution is to loop the SLS line and run with standard Bilsteins. You'll need the 23mm rear spring shims (most likely) to have the car sit level. That costs about $500 for all four shocks. Much cheaper than OEM.

Do yourself a huge favor and change the serpentine belt, fan clutch, radiator, thermostat, and water pump. It's not really that hard if you're a DIY-er. If not, get it done at a good Indy shop. Don't let dealers muck around with your car unless you're very close with them. It takes a special person to deal with these M120 engines. Additionally, use the search to look up the "cool harness." Instead of that route, I've installed SPAL electric fans in all of my race cars, Mercedes, BMW's, etc. Everything except a few Italian exotics and my F350 monster have SPAL fans and I swear by them. Most people think it's too hard, too expensive, etc... well it's BS. It'll drop your engine temps by about 5 degrees celsius if not more. At least that's what I've found out.

How many miles are on your S600? Is it a five speed or four speed tranny? How many owners since new? Where was it located before you bought it?

Enjoy and welcome aboard!
Ricky

One more thing, run ONLY Mobil 1 oil and change every 3k miles on the dot. I change my oil every 1000-2900 miles. My mother changes hers every 2500-3k. We use Mobil 1 0W40 and Michelin tires. Nothing else for our cars! Another little thing I do, and at this point you probably think I'm crazy but what the hell, is I only fill up my gas when it's cool outside, there are no other cars filling up, and only using Shell premium.
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Old 06-27-2011, 03:03 PM   #3 (permalink)
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Quote:
Originally Posted by MB_Fahrer View Post
You've got the middle model--which I like much better than the '96+ 140s--that can have wiring issues.
Just to be absolutely clear, because Ricky's wording is possibly misleading, it was the early models up through 1995 that had wiring harness issues. The first thing you should do when looking at any 1990-95 Mercedes is check the engine compartment wiring.

Quote:
Originally Posted by MB_Fahrer View Post
One more thing, run ONLY Mobil 1 oil and change every 3k miles on the dot. I change my oil every 1000-2900 miles. My mother changes hers every 2500-3k.
OK, I'll agree with most of what Ricky said as good general advice, but not this part. I don't see any indications that a 3,000 mile oil change interval is necessary, particularly with modern synthetic engine oils. Pick your favorite synthetic and do frequent changes but 3,000 is probably a little overkill, unless you hit a time limit rather than miles. Personally, I do a 1 year or 7,500 mile interval. Some people do 10k. Some do 15k. The last several years, I've changed oil at the 1 year mark with miles below 7,500. A couple of times it may actually have been close to 3,000 miles for the year.

Brett

Last edited by Brett San Diego; 06-27-2011 at 03:07 PM.
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Old 06-27-2011, 03:06 PM   #4 (permalink)
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Quote:
Originally Posted by Brett San Diego View Post
Just to be absolutely clear, because Ricky's wording is possibly misleading, it was the early models up through 1995 that had wiring harness issues. The first thing you should do when looking at any 1990-95 Mercedes is check the engine compartment wiring.


OK, I'll agree with most of what Ricky said as good general advice, but not this part. I don't see any indications that a 3,000 mile oil change interval is necessary, particularly with modern synthetic engine oils. Pick your favorite synthetic and do frequent changes but 3,000 is probably a little overkill, unless you hit a time limit rather than miles. Personally, I do a 1 year or 7,500 mile interval. The last several years, I've changed oil at the 1 year mark with miles below 7,500. A couple of times it may actually have been close to 3,000 miles for the year.

Brett
Sorry about that, you'd think I'd learn to quit multi-tasking while trying to type lol

I agree that the 3k is overkill, but at $40k for a replacement motor and parts as expensive as they are, a little overkill can be a good thing
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Old 06-27-2011, 03:33 PM   #5 (permalink)
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The newly installed poster asked how durable the V12 motor on a 1995 W140 was and for that you should know:

The engine was in development by Mercedes for at least 10-years before release.

This motor is referred to as the M120 motor. It is the first incarnation of the Mercedes V12 for modern automobiles. Subsequent V12's that wound up in the 220/221 first of all were/are less powerful and smaller displacements due to environmental concerns. This applies to their NATURALLY ASPIRATED state. MB attached turbochargers to squeeze more power out of their 2nd generation V12's and those are MORE powerful than the M120, but they are NOT naturally aspirated, a factor in determining long life. Natural aspiration is far better for longer engine life.

But the M120 motor is a very strong, very stable motor if treated with respect and given the care prescribed by the factory. I particularly like the idea that the aluminum cast block was made with silicon (sand), so the cylinder walls are more glass-like with no need for cast iron sleeves.

The M120 motor can go virtually forever, given the care and respect it deserves. It's a very long-lived motor.

The transmission, on the other hand, is another story...for another day...
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Old 06-27-2011, 04:10 PM   #6 (permalink)
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S600 Follow-up...

great, thanks alot for all your input. very informative!

following is what i posted earlier on a separate thread regarding my S600 and a shifting problem getting repaired now. on another forum someone suggested the trans down-shift linkage/solenoid may be at fault, which seems plausible.

so a few days ago i purchased a beautiful '95 S600 ($7200, San Diego Lexus), 123K miles, 2 owners, calif reg'g/domiciled since new. when i get the car back i'll post some pics here.

she test drove just fine before the purchase. while the salesman followed me home saturday in the S600 he noticed the trans intermittently down-shifting from 4th gear to 3rd gear while cruising on the HWY. anyway he was honest enough to point this out to me when we arrived at my home and immediately called their indy shop to pick up the car for repairs.

having done quite a bit of maintenance on my 280E,300E and 300D, i figure the S600 trans problem couldn't be that serious. i'm thinking something to do with the shift linkage/bushings, trans vacuum modulator or throttle linkage/sensor to the transmission. whatdaya guys think? prior to sale the dealership replaced the engine oil pan and trans oil pan gaskets. perhaps they didn't properly reassemble the trans linkages.

anything else you could suggest doing for preventive maintenance much appreciated. i also see the rear shock accumulators need to be replaced. very stiff rear suspension.

and can i get someone on benzworld to run my VIN to dump all of the mercedes dealer maintenance history? i recall doing this on a benz or BMW forum years ago.

all of your ideas and suggestions very much appreciated!

cheers,
rick

'73 280E
'90 260E
'77 300D
'93 300E
'95 S600
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Old 06-27-2011, 04:55 PM   #7 (permalink)
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Date registered: Aug 2008
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response...

Quote:
Originally Posted by MB_Fahrer View Post
Between my mother and myself, we have six V12 W140's and R129s. They are very reliable if you treat them properly and stay ahead on maintenance. You've got the middle model--which I like much better than the '96+ 140s--that can have wiring issues. Have the top engine harness replaced. I've got a source for them at a reasonable $750. From the stealership they aren't too much more.

The suspension is one of the worst systems on your car from a cost perspective. It's right about $4k in parts to replace shocks and springs. Front shocks are almost $1k and rears are about $700. A cheaper solution is to loop the SLS line and run with standard Bilsteins. You'll need the 23mm rear spring shims (most likely) to have the car sit level. That costs about $500 for all four shocks. Much cheaper than OEM.

Do yourself a huge favor and change the serpentine belt, fan clutch, radiator, thermostat, and water pump. It's not really that hard if you're a DIY-er. If not, get it done at a good Indy shop. Don't let dealers muck around with your car unless you're very close with them. It takes a special person to deal with these M120 engines. Additionally, use the search to look up the "cool harness." Instead of that route, I've installed SPAL electric fans in all of my race cars, Mercedes, BMW's, etc. Everything except a few Italian exotics and my F350 monster have SPAL fans and I swear by them. Most people think it's too hard, too expensive, etc... well it's BS. It'll drop your engine temps by about 5 degrees celsius if not more. At least that's what I've found out.

How many miles are on your S600? Is it a five speed or four speed tranny? How many owners since new? Where was it located before you bought it?

Enjoy and welcome aboard!
Ricky

One more thing, run ONLY Mobil 1 oil and change every 3k miles on the dot. I change my oil every 1000-2900 miles. My mother changes hers every 2500-3k. We use Mobil 1 0W40 and Michelin tires. Nothing else for our cars! Another little thing I do, and at this point you probably think I'm crazy but what the hell, is I only fill up my gas when it's cool outside, there are no other cars filling up, and only using Shell premium.
thanks for your detailed overview. my S600: a few days ago i purchased a beautiful '95 S600 ($7200, San Diego Lexus), 123K miles, 2 owners, calif reg'g/domiciled since new. got orig complete books, manuals and sticker/ invoice. moonstone gray paint, parchment interior. $134,170...out the door, incl $3,000 guzzler tax! LoL. when i get the car back i'll post some pics here.

i believe its the 4-speed tranny. i do my own maintenance. yes, i had previously read about the S600 engine wiring harness reliability problems, insulation breakdown. i have not inspected mine yet but already prepared to replace it if needed. who is your source for the $750 engine harness? is it a sub-section of the engine compartment wiring or the entire engine compartment, soup-to-nuts?

she test drove just fine prior to the purchase. while the salesman followed me home saturday in the S600 he noticed the trans intermittently down-shifting from 4th gear to 3rd gear while cruising on the HWY. anyway he was honest enough to point this out to me when we arrived at my home and immediately called their indy shop to pick up the car for repairs.

having done quite a bit of maintenance on my 280E, 300E and 300D, i figure the S600 trans problem couldn't be that serious. i'm thinking something to do with the shift linkage/bushings, trans vacuum modulator or throttle linkage/sensor to the transmission. whatdaya guys think? prior to sale the dealership replaced the engine oil pan and trans oil pan gaskets. perhaps they didn't properly reassemble the trans linkages. a member on another forum suggested looking for a faulty kick-down switch, solenoid or linkage to the trans.

apparently the rear suspension accumulators are shot as well. rear suspension very stiff, no floating for this teutonic yacht. too bad i just had surgery on my shoulder last week so mechanically i'm benched for a few more weeks.

good advice on the mobil-1 synthetic. i was not sure if it would be a good idea to run synthetic on one of these motors +100k miles.

i would really like to get the MB dealership VIN maintenance history dump, as i was told the previous owners had it serviced locally there. from my research it doesn't look like they will give it to me, although i have not asked yet, and i don't see any forum members doing favors in that regard.

cheers,
rick

'73 280E
'90 260E
'77 300D
'93 300E
'95 S600
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Old 06-27-2011, 06:27 PM   #8 (permalink)
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Moonstone is a terrific color. My first S600 was a 1995 sedan in moonstone with lighter gray two-tone interior. Gorgeous car. Black may be more 'impressive' but the dark gray moonstone color is my favorite. Have you noticed how plush the carpeting is? I think 1995 was the only year the carpet was of a higher grade than other years. I used to drive my 'old' S600 without my shoes, it was that plush and comfortable.

Anyway, there are TWO harnesses: the engine harness (lesser one) and the body harness (the greater one). Both had the soybean insulation and need to be replaced, but replacement units are 'normal' and will serve the life of the car. So replacement of the harnesses is a one-and-done deal.
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Old 06-28-2011, 09:00 AM   #9 (permalink)
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[QUOTE=mfr3;he noticed the trans intermittently down-shifting from 4th gear to 3rd gear while cruising on the HWY

1. Before you do anything, it is imperative that you have the dealership pull the codes. If you can find a Indy to do this it will be less expensive.

2. There is a pressure transducer sensor on every Mercedes transmission which is called a overload protection switch. As the name implies it protects the transmission by causing a downshift when the transmission becomes overloaded (too high hydraulic pressure). If this sensor is faulty it could cause the symptoms you describe.

3. The downshifting could also be caused by small partcles (clutch debris, etc) getting lodged in the fluid channels or seals, affecting internal pressures. You should have the transmission fluid and filter changed.

Good luck.
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Old 06-28-2011, 03:32 PM   #10 (permalink)
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The overload sensor doesn't cause transmission to downshift. It sends the signal to the ignition control module to retard timing.
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