w126 comparison question: m103 v om603 - PeachParts Mercedes-Benz Forum

ruchase · #1 03-09-2014, 01:52 AM

I'm wondering how the m103 compares to the om603 (besides the obvious gas/diesel)...I have a '86 300sdl going very strong at 280k miles but I would like to eventually replace it with a '90 300se. Several reasons for this switch: 1) The 300se is a more 'city friendly' car. 2) I've thought about an early 300sd, but going from a 603 to a 617 will be painful. 3) Finding a good 350sd would be a costly enterprise; not to mention concerns with the larger bore 603s.

I feel like the m103 powered 300se should provide a close enough driving experience - maybe even better being a gasser in a smaller/lighter car. This is an acceptable trade-off for me in light of the higher gas consumption.

What kind of reliability can I expect from well maintained m103? Besides cosmetic differences, are there any major differences in the m103 w126 cars from the 1988 through 1991 model run?

My goal would be to find the lowest mileage and best maintained example in the $4-5k price range. Thanks!

pawoSD · #2 03-10-2014, 09:33 AM

Why would a 300SE be a more city friendly car? Its going to be slower off the line unless you mod it to do 1st gear start... They are also lucky to get 18mpg in the city on premium.

A 300SE will be more trouble than a 300SDL, especially if it was not very well taken car of by the previous owner.

I have a 420SEL and it is a very enjoyable car. The I6 just doesn't have enough torque to handle such a big car.

oldsinner111 · #3 03-10-2014, 10:40 AM

weak engine unless you turbocharge it.Your diesel should go 500,000 miles or more.

pawoSD · #4 03-10-2014, 12:16 PM

The m103 is even pretty leisurely in a W124...in a W126 it will fall into the "slow" category. I am only willing to drive a slow car if it gets great MPG.....like my 190d.

My 420 slurps fuel like a beast but its also nice and fast, so its fine with me.

compu_85 · #5 03-10-2014, 12:26 PM

The 350's toruqe is great in the city

-J

DieselPaul · #6 03-10-2014, 12:35 PM

Quote:

Originally Posted by oldsinner111

weak engine unless you turbocharge it

What!?

ruchase · #7 03-10-2014, 10:12 PM

Quote:

Originally Posted by pawoSD

Why would a 300SE be a more city friendly car? Its going to be slower off the line unless you mod it to do 1st gear start... They are also lucky to get 18mpg in the city on premium.

A 300SE will be more trouble than a 300SDL, especially if it was not very well taken car of by the previous owner.

I have a 420SEL and it is a very enjoyable car. The I6 just doesn't have enough torque to handle such a big car.

Even though it's just a few inches longer, the SDL just feels like a barge compared to my previous SD, especially when parking in city parking structures.

I thought the m103 was generally a trouble free gasser minus the CIS quirks.

Quote:

Originally Posted by pawoSD

The m103 is even pretty leisurely in a W124...in a W126 it will fall into the "slow" category. I am only willing to drive a slow car if it gets great MPG.....like my 190d.

My 420 slurps fuel like a beast but its also nice and fast, so its fine with me.

If I could find a local euro 420se in decent shape I'd jump on it.

ruchase · #8 03-10-2014, 10:17 PM

Quote:

Originally Posted by compu_85

The 350's toruqe is great in the city

-J

I've seen a few 350sd's pop up locally from time to time; I'm just afraid of what I might be getting myself into. My 300sdl has been a wonderful, trouble free DD, but I can only imagine how different my outlook on the 603 would be if I had to deal with major engine repair.

I'm open to the right 300sd...if it is clean and has good service records, I'd consider it. Also thought about a w116 which is by far my fav 's' class benz; but parts are getting scarce for them, so I don't know if it would make a good DD.

pawoSD · #9 03-12-2014, 09:51 AM

420SEL or 300SD, both excellent cars. The 300SDL is good too, I would not want a 300SE over a 300SDL....the M103's fuel injection system can be a pain to keep running properly, and its not very efficient. Low end torque is weak, which makes it slow in such a big car.

For some reason I have found the fuel injection on the V8's to be much more reliable than on the I6 motor.

Hit Man X · #10 03-13-2014, 01:43 PM

The M103 powered W126s are dogs and have horrible fuel economy as you will always be on the pedal to accelerate them. Avoid them. The M103 belongs in W124 and smaller vehicles.

The thing does really low teens in the city in the summer with the A/C on and the fan clutch locked...so does my 560SEL but that can get out of its own way without breaking a sweat. On the freeway the 300SEL can do 19-20mpg on a good day driving 60-65mph.

If everything mechanical was not 100% on mine, I would have unloaded it long, long ago.

420s seem to be the best combination of simplicity (no SLS, no power recline rear seats), power (around 30ft-lbs on the M103, about 1000 RPM sooner), and fuel economy (burn 87 just fine). If I was after another W126, this is probably what it would be.

Obviously SD and SDL will be superior to any CIS I6 or V8 in terms of fuel economy. SDL's have an excellent A/C compressor factory and SD's are plagued with that garbage R4. Places like Klima Kit and European Cooler Air offer Sanden swap kits for the 617, which is pretty much a 'must have' to me. I did mine a few years ago and it is hands down the best thing I have done for my SD

Hope it helps.

lorainfurniture · #11 03-13-2014, 02:27 PM

The m103 engine in the w126 will get you neary 20mpg no matter how you drive it. I dont understand what people are talking about when they say it is powerless. When I had my 300se, I could chirp the tires when I mashed it, and it kicked down to 1st gear. With a 3.47 diff I don't understand what these guys are talking about.

The 300se's big problem is that on the freeway, 70mph is like 4k rpms.

Keeping the m103 running PERFECTLY is a bit of a challenge. It needs spark plugs every year or so, and full ignition tune up every 5 years give or take based on the average 15k miles per year.

Cis-e injection system is pretty easy, once you understand how simple it is. The trick is to maintain the ignition system, and keep the vacuum tight arounf 13-15hg.

Problems with the m103 are:

Oil leaks. Its not a matter of them leaking, its how much..... I was actually able to get my 300e completely leak free for almost a whole year.

Lack of PO maintanence. Deferred maintenance will run you at least $500 in QUALITY parts. Dont skimp or you will be sorry. Thats just tune up stuff.

A lot of these people never owned a 300se, so are going on second hand opinions.

pawoSD · #12 03-13-2014, 07:55 PM

There is no way a M103 will do 20MPG routinely in a W126. No way no way. My W124 with a M103 averaged 16-17Mpg doing mostly city miles, and that was a lighter, more aerodynamic car. And that was when the engine WAS running well, which it often was not....when not it was more like 12-14mpg.

My 420 averages about 18-19 city if driven gently, 15 or so driven like a maniac, and about 23 highway on cruise at 75mph with no A/C....about 21-22mpg with A/C.

It seems like the Ignition and CIS on the M102/M103 is much more finicky than on the M116/M117 engines too.

The small old gassers aren't worth the trouble, not enough power and bad fuel economy. The V8's and diesels are much more fun. The only smaller gasser I am a fan of so far is the M112 V6...its a beast. Mine has 132k on it and is bone dry and runs beautifully. Far superior to the M102/M103.

lorainfurniture · #13 03-13-2014, 11:14 PM

Quote:

Originally Posted by pawoSD

There is no way a M103 will do 20MPG routinely in a W126. No way no way. My W124 with a M103 averaged 16-17Mpg doing mostly city miles, and that was a lighter, more aerodynamic car. And that was when the engine WAS running well, which it often was not....when not it was more like 12-14mpg.

My 420 averages about 18-19 city if driven gently, 15 or so driven like a maniac, and about 23 highway on cruise at 75mph with no A/C....about 21-22mpg with A/C.

It seems like the Ignition and CIS on the M102/M103 is much more finicky than on the M116/M117 engines too.

The small old gassers aren't worth the trouble, not enough power and bad fuel economy. The V8's and diesels are much more fun. The only smaller gasser I am a fan of so far is the M112 V6...its a beast. Mine has 132k on it and is bone dry and runs beautifully. Far superior to the M102/M103.

I get 21 mpg in my 300e and I kiss the redline every day. Road trips have netted me nearly 26mpg. My 300te 4matic runs like pure crap and I still get 14 mpg.

I won't deny that v8's are much more fun.

When I owned my 300se I averaged 20 mpg, seeing as high as 22, and low of about 17. You should bring your m103 over sometime so I can get it to run right for you.

JamesDean · #14 03-15-2014, 02:37 PM

Quote:

Originally Posted by lorainfurniture

I get 21 mpg in my 300e and I kiss the redline every day. Road trips have netted me nearly 26mpg. My 300te 4matic runs like pure crap and I still get 14 mpg.

I won't deny that v8's are much more fun.

When I owned my 300se I averaged 20 mpg, seeing as high as 22, and low of about 17. You should bring your m103 over sometime so I can get it to run right for you.

These numbers sound right to me. The 3L m103 in my 190E was getting me 24-25 mpg on the turnpike doing 70-75.

The 420SEL does 20mpg at 70-75mph.

I drove the 560SEL home from NYC and it averaged about 21-22 on the freeway.

Wayfarer · #15 04-10-2014, 10:21 AM

I have a '91 300SE with 97K miles on it and I love it. It has been 100% reliable. I bought it from a friend 4 years ago who had it since 30K miles, and it was 100% reliable for him too.

I do my own maintenance and recently (at 90K) did a full tune up and it was a true pleasure to work on. Other experiences vary, apparently, but my M103 runs perfectly. I have a pretty good knowledge of CIS engines and did have to tweak the base fuel mixture a couple years ago to get it running smoothly again. So you may have to know a little about CIS engines, or know somebody who does, to have it run smoothly. But there are a bazillion M103's out there with good forum posts on diagnosing and repairing every aspect.

Power is not too bad, and I have owned a 560SEL and so can compare directly the W126 6's with the 8's. I agree it isn't the greatest on the highway, it really needs and overdrive! But around town, where I do most of my driving, it's actually just about perfect with it's short gearing and rear end ratio. You just need to have a slightly different philosophy when driving it and not expect too much. I just sort of "ease" around town, and the engine is buttery smooth and quiet. As long as you don't ask too much of it, or think it should drive like a sports car, then it will give you a great around town driving experience.

The short wheel base make a surprisingly BIG difference in the way the car handles even around town. The short wheel base W126 isn't exactly a sports car, far from it, but it isn't bad. Decent turning radius, and the whole car feels simple and robust. The long wheel base "L"'s are just huge boats in comparison. Don't know why it makes such a big perceived difference, but it does. I like the 300SE a LOT and the short wheel base has a lot to do with it.

Overall, I think the M103-powered W126 300SE is a great car, especially around town, not so much on the highway. It's the mating of two classic Mercedes designs: the W126 with the M103.

Oh, and I get 17-18 mpg in town and 21-22 on the highway.

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