M103 discussion thread.
 

I deleted my previous thread to focus more on the subject at hand, being the M103 specifically.

Some general and generally helpful questions:

• Are there any common faults with this engine?

• Commonly, what components tend to fail at what mileages?

• What useful mechanical knowledge specifically about this engine might come in handy for the shade tree wrench(wo)man?

Any additional suggestions for this list are very welcome!

Did you do a search? You will find all kinds of stuff to keep you busy reading for days. Seriously, there is a TON of info on common M103 issues. It's one of the most commonly used MBZ engines.

Most common fault is the head gasket.
It can start leaking even at low mileage.

If the car has sat for a time you may find leaks in the transmission caused by seals drying out.

Electrics and minimal electronics are basic and usually present no major problems.

Hard starting problems sometimes caused by a bad OVP or fuel pump relay.

Vacuum leaks due to brittle vacuum lines.

Fairly easy to work on as their is ample room in the engine bay.

Personally I think the M103 is a great engine. Figure on top end at about 200K. Same with timing chain and guides. This is from personal experience though. Others might have had to change earlier (or later). There are small things that go wrong like the monovalve. No big deal but I think that most of us that have had a w126 or something similar have had to take care of this.

Well, I bought it: 1991 300SE. 188,000k on the odometer.

Wow, that really concerns me to hear about the head gaskets. I had to do a head gasket replacement on an '87 Cadillac DeVille and it was NOT FUN; probably owing to the fact the the GM HT4100 is the worst engine ever designed...or rather, not designed (since "design" tends to suggest some semblance of mindful effort).

Now I'm fearful that maybe I shouldn't take it on a long road trip as I had been planning...

I can contest to the fact of the head gasket problem on the M103. My car only has 100 k kms or about 63 k miles and the head gasket is needing replacement. By all indications such as the amount of oil on the block and belly tray it has been leaking for some time. It is an inevitable problem that you will face. And as you can see even a low mileage car can experience the failure early on. OM618: you can probably tell if your head gasket needs to be done. Oil leaks on the ground where you park as well as an oil block and high oil consumption are indicators. The best thing to do is monitor the oil level and calculate how much is is using per 1000 miles. With that kind of mileage though, I would suspect that the head may have been removed and the gasket replaced at some point during its life.

Great road trip car. Next you'll be back asking if the motor is supposed to run at 4,000 RPM at cruising speed. You'll be pleased to learn that, yes, the M103 is a little beast designed to RUN HARD. Change out the fluids and filters and hit the road. Enjoy!

I've been digging around the forums and I've been finding some really good stuff.

But, it seems like I was possibly a bit too hasty in my purchase.

I'm a long time Benz admirer (W126 w/OM617 most noteably), but a completely green Benz owner (including the 83' 300SD I bought a week ago that now cranks but won't start...).

My gut instinct was that this '91 300SE would likely go for another 60k+ under moderate driving without needing any major repairs, but I'm begining to fear that this 188k on the odometer might lead to a 300SE on jack-stands rather quickly...

EDIT: Yes, I suppose that at 188k that if this problem is quite frequent that the HG would have been been replaced by now...I'll have a better look under the hood and under the engine this weekend.

Final sales price was $3145. Cosmetically it's quite practically flawless. Hopefully it's heart is as pristine as it's body.

great hwy driver, I had bad valve guides but no heating or head gasket issues at 1400000 1 quart in 300 miles, I did the chain because I was there and did have rocker arm problems

IMHO anybody that buys a 17 year old car with 188k on the clock for 3K and then hopes it will go another 60K miles without needing any major work is looking at the world through rose colored glasses.

I sure hope you are right but I'm betting your "gut" feeling ain't going to pan out.

Well that feeling was in part elicited by my knowledge of the outrageously reliable OM617 and extensibly, being an engine produced by MB during the glory days (imho) of the W126 and over-engineering the heck out of their motors and chassis, I expected "comparable" (for a gasser) performance out of the M103.

I failed to consider my prior experience with aluminium heads and aluminium engines in general. I was hesitant to buy this car and instead hold out for a comparably well kept W126 with either an OM617 or OM602, but I'm really in need of reliable (and stylish!) transportation immediately so I gave in.

Hopefully some of the MB mechanical noteriety I was expecting will shine through with this particular M103 block...at least for another 20k or so...

I certainly hope it will as well, if its in nice shape now and has had reasonable maintenance in the past I'd say you have a pretty good chance of making that goal.

But keep in mind you are driving a 17 year old car that is now approaching 200K on the odometer - when you get that far down in the life cycle of ANY car pretty much anything is possible.

I agree wholeheartedly with Tim.

At this point it is up to luck, the previous maintenance, and your own PM. You could lose anything from wipers to a headlamp switch, everything mechanical fails eventually.

If you decide to bail, I've got a nice reliable 603-powered 124 available, ...

so far 15000 since valve job and still runs great but I have a vibration issue that I will get to when I get back on my feet

OM, we seem to have common ground here: I had an Eldorado with the infamous 4100 engine that kept me pretty busy for about 9 years.
For the last 17 years I have had a pristine '91 300SE, and it has just about 180k miles, as yours does. I have had the usual water pump, alternator, idler pulleys, belt tensioner issues; I attribute much of this to the high revs the engine turns in the S-class car.
I also replaced the head gasket several years ago. The reason the head gasket fails is simple material properties; you have a very long aluminum head sitting on an iron block. The difference in expansion rates causes the head gasket to drag over the deck surface every time the engine heats and cools.
Mine manifested itself as a water leak near the right rear. The valve stem seals were lousy from the start, with the engine always burning oil on the highway. I did the R&R myself (pretty easy to do) and had the head freshened at a local shop, including valve job, guides, seals, and planing, for about $300 or less, I think. Since then, no oil usage, and it runs great.
There are other little issues on the M103, like the front cover seal that always oozes, and sagging motor mounts. But the head gasket issue seems to be the only major problem; and fixing that every 10 years or so is not in my mind an indication of a non-durable design.

Would I take this car on a long trip - no, not since it stranded us last year with a busted belt tensioner right out of the blue. But, do I trust it to get my wife safely to work every day for the next 10 years - absolutely.

DG