I’m looking at a few, like the size , wondering what are the common issues. I’ve owned a 420 sel and many diesels and a e320.

I know rubber stuff is old, mounts, vac hoses etc. what kind of longevity if they have been maintained and what about change timing belt interval

Are you talking about a 126 or 140 version?. Either one will get about the same mileage as the v8 version but will have much less power.

Good folks like Mike Murrell and Hitman X love their 300SELs so the M103 in W126 has a fan base. Among an ‘87 SDL, ‘91 300SE, ‘93 300SD and ‘95 S420, the 300SE was my least favorite. Fuel economy vs S420 was negligible for me (above 70 the S420 was more economical), high revs on the freeway gets tiring though it’s not loud or buzzy, can’t keep up with a V6 Camry, it’s really frustrating to sort when an M103 decides it doesn’t want to idle glass smooth. And if you’re in California, an M103 300SE will likely require test only station smog checks which where I am means limited discount and coupon options. Basically state emissions statistics brand it a gross polluter.

For 88-91 300SEs, everything about the W126 applies and everything about the M103 applies. I don’t think the M103 necessarily needs a new chain on interval like contemporary V8s. I think you can go based on elongation. Change it every 150K miles if you must but there aren’t a lot of M103 broken chain threads. Finding someone to service an R12 system is difficult. Shops would rather convert to R134a which generally diminishes cooling performance but shouldn’t be a deal killer in NorCal. I expect PBU service will be due, a side from the refrigerant system and vent actuators. The PBU just gets old and cranky. Quality rebuilt units are available and easy to install. Vent actuators less so but you can do most without pulling the dash.

If you’re looking at 92-93 300SEs, that’s a different car and engine altogether.

Sixto
98 E320s sedan and wagon

I just had a ‘89 300SE last summer. Only kept it a few months. Beautiful light ivory over palomino leather, euro lights and chrome wheels. A rather high 3200 rpm at 65mph, which by the way is the same as the 81-84 300SD. Insufficient leg room in the back for such a big car. Slow/sluggish take-offs, however, pulls like a freight train at speed. And yeah, the idle was terrible and I couldn’t figure it out. Lots of oil leaking too and tranny fluid as well. A/C was still r12 and was the coldest a/c I have ever experienced in any car. Froze me the hell out. But in the end, I told myself that if I was to get another w126, it would have a V8 and long body... and now I have a 560SEL.

the w140s the early ones have better leather,but crappy trans,and wiring.98s,and 99 have better stuff,I have never had trouble with a head gasket,had my car 9 years,however I run a alternate thermostat.76c.

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1999 w140, quit voting to old, and to old to fight, a god damned veteran

I've seen an unusual number of six cyl W126 gassers here in the midwest, and they are in much better condition than the v8 cars I see on average. No idea why, but it's made me ponder such a few times. I can't imagine they aren't pretty doggy, and that they don't get pretty bad MPG around down trying to lug that much car from stoplight to stoplight.

Wonder what an M104 w126 sedan would be like..

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One more Radar Lover gone...
1982 VW Caddy diesel 406K 1.9L AAZ
1994 E320 195K

The 300 SE is a good "town car", and I think the second gear start on most is what makes them sluggish off the line. Maybe there's a way to modify the second gear start to always start in first.

The M103 has a timing chain, not a belt, and it should last for nearly the life of the engine. The thing that wears timing chains is dirty oil.

Removing the R16/1 resistor increases spark advance faster with revs, so low end torque is better.

CA has labeled the M103 as "high emitter profile", not a "gross polluter" unless the subject car exceeds the gross polluter cut points, and all will likely be directed to a "test only facility". I have one less than a mile away. It's a "drive through" type and they accept coupons, so the typical cost including the "smog certificate" is about 50-60 bucks.

Emissions will be much lower if you short the R16/1 resistor connector and disable the vacuum advance. I did extensive testing on this setup and documented the results here in a couple of threads about 10 years ago. Search for threads started by me and R16/1 resistor.

BTW, there is a CA Web site where you can input the license number and get the emission test history in terms of pass or fail. I think it might be the Bureau of Automotive Repair site. They manage the CA emission test program.

The 1:1 top gear and 3.46:1 axle means high revs as stated at freeway cruising speed, but the engine is very smooth at speed, and has a pleasant muted "growl" that is typical of high output inline six-cylinders.

M103 idle smoothness is an issue. Be sure to use non-resistor spark plugs. Resistor type will roughen the idle. Also, I think the KE-Jetronic fuel system may be an issue since idle fuel pressure is low, which causes uneven fuel distribution compared to modern EFI systems.

In addition, the M103 has a pretty aggressive cam in terms of duration and overlap, which is what makes it so rev-happy, but manifold vacuum is relatively low at idle, especially in drive with an automatic. Any engine that idles at about 14-15" Hg or less manifold vacuum will exhibit some "lope" due to valve overlap - similar to sixties vintage Corvette engines like the 327/350 HP engine that has a "hot" hydraulic lifter cam. It's idle behavior is 14-15" @ 750 in neutral with a slight lope.

Duke

Yep, as Sixto pointed out. I love mine due to the simple I6...like an E23 BMW, but realize it does nothing very well. It does not run off a stop light well. Fuel economy is easily similar as my 560, granted my 560 has true duals now off a 9:1 Euro motor so it does breathe MUCH easier if you have never seen that driver to passenger crossover pipe (1-5/8" OD, NO JOKE). It is somewhat noisy on the freeway but will run all day long at 60, 70, 80, 90. Whatever. I think it is out of gear around 125mph at 6400rpm area. I still give mine full power 3-4 upshifts around 90mph, car seems to like it.

I did manage to squeeze out 21mpg freeway going 65mph once with no headwind on I45 south and the AC off. I guess it averages 14-15mpg. City only in the summer barely gets out of the teens, maybe, as the AC is always on here in Texas and the fan clutch is roaring. Freeway summer tends to be high teens going about 70-75mph...limits are now 70mph in most of Texas so I have to try to keep up.

The SDL can damned near take it 0-60mph. M116/7s always need valve guides with age, otherwise the 420SEL is the best bargain around to me. Decent torque, decent top end HP, decent fuel economy. Less crap to break down compared to the 560. No SLS, no power rear seat.

My 300SEL also has been exempt from emissions for years, so speak with Duke on that. His knowledge how to pass that is NOT something to ignore.

BUT!

The M103 is a very simple engine. Yes, they leak oil. 97% can be fixed easily. A 25 year old front main is going to leak. The fan bearing bracket o-ring is often forgotten when replaced. If the lower cover leaks, spend the $40 and buy OEM sealant. Buy an OEM 'U' shaped upper timing cover gasket. Same for the valve cover gasket, the aftermarket are garbage. I finally became fed up with the TTY head bolts and went to ARP studs, my No 6 cylinder oil leak is gone. Only use the OEM tensioner. Sachs fan clutch. Otherwise you will make yourself crazy. OEM motor mounts. Idler bushing replacement requires dropping exhaust.

The Superior Transmission valve body kit is a must for the M103/W126 to me. It allows you to tone down that crazy harsh 1-2 upshift. Then you will be able to make use of that gear if needed once you dial in line pressure and bowden slack. That will take some farting around to dial in exactly.

My catalyst was also partially plugged due to the oil consumption the thing had for years. I gutted it a few years back and power gains are noticeable. The vehicle is now much easier to roll out in second gear with the AC running and fan clutch locked. Head job at 275k area cured that and picked up nice power. Cold compression test was 160-170psi on all six cylinders and crosshatching was still nice at 310k area when I did ARP studs and OEM gasket.

It is easily the least expensive W126 to keep on the road that is not Diesel powered. Power application can be sorted once you figure out throttle input/trans shifting to keep it on the cam. The car cannot be lugged at 2000rpm like a V8, it simply has no power to do this.

Would I buy another? Probably if the deal was right.



Hope it helps!

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I'm not a doctor, but I'll have a look.

'85 300SD 245k
'87 300SDL 251k
'90 300SEL 326k

Six others from BMW, GM, and Ford.

Liberty will not descend to a people; a people must raise themselves to liberty.[/IMG]

Sixto and others in this thread brings up some good points.

If I had it to do all over again, I would have sought out an 88-91 420-SEL. Better gas mileage and lower revs at hwy speed. The 88-91 300-SE/SEL turns 4000 rpm at 70 mph.

The biggest complaint I have about the 88-91 300-SE/SEL also applies to other cars from and before that era...parts availability. It's getting harder and harder to find "good" parts for these cars. Junk yards are ok for specialty bolts/brackets, but not for anything truly mechanical/electrical. It's depressing when your only option is a part manufactured in China...ie...URO or maybe worse, nothing available at all. MB is not the only mfg. with this problem. Asian mfgs. are also making it harder to find parts for older cars in that genre.

My 2 cents.

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Mike Murrell
1991 300-SEL - Model 126
M103 - SOHC
"Fräulein"

Mike, aren't parts available from a MB dealer or the Classic Center? I realize their prices may be significantly higher than aftermarket prices, but quality parts should be available for older MB vehicles.

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Fred Hoelzle

I buy a lot of parts from Jon at the classic center. Their prices are pretty reasonable for OE parts in my opinion. If you're part of the car club you get 10% off on parts from the classic center and dealers.

I have a 1991 300SE.
I usually pull 22-24 mpg highway at 70 mph.
City usually 17
It's slow, a/c compressor kick on is vey noticeable.
I've never driven a 420 or 560 so I can't compare.
Head was rebuilt 30k miles ago, doesn't burn any oil but the head gasket is leaking externally back by cylinder 6. The next headgasket will be #4 since this car was new.
It screams on the interstate, but the engine loves it.

I would definitely buy another 300se, my next w126 I'll purchase based off condition of the car and not so much engine.

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"It's what non-car people don't get. They see all cars as just ton-and-a-half, two tons of wires, glass, metal and rubber. That's all they see. People like you or I know, we have an unshakable belief that cars are living entities..... You can develop a relationship with a car, and that’s just what non-car people don't get."
-Jeremy Clarkson

Man, four head gaskets?


Anyone ever make an aftermarket MLS one and some good head studs?
That usually fixes most HG prone motors for good unless there is crazy boost involved.

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One more Radar Lover gone...
1982 VW Caddy diesel 406K 1.9L AAZ
1994 E320 195K

I went OEM MB head gasket and ARPs, my oil leak is gone back there. tired of dicking with those TTY fasteners. Valve cover gasket weeps some, just been lazy to fix.

Just took mine on another extended trip. Did 20.4mpg at 75-80mph with the A/C off and no head wind. 17.8mpg with A/C on doing 80-90mph. Creeping on 323k. Guess gutting my partially plugged cat helped my economy more than I expected.



ARP AU-5.400-1LUB is the stud needed
M12x1.75 nut
And washers

I think I bought a pack of '251-4701' for 10 of the 12 needed.

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I'm not a doctor, but I'll have a look.

'85 300SD 245k
'87 300SDL 251k
'90 300SEL 326k

Six others from BMW, GM, and Ford.

Liberty will not descend to a people; a people must raise themselves to liberty.[/IMG]

Never think of the 300SE as slow, the 2017 Suburbans I drive for work ain't that much quicker. And I prefer driving fast in a slow car over going slow in a fast car, more fun in my opinion and no tickets...

Mileage in the city is abysmal, even on a good day you can see the needle move to the left. I prefer the the SE over the SEL because of it better handling and "less" body roll. Less complicated than the 560SEL was also a selling point for me, didn't want to go bankrupt as it is my daily driver. Motor mounts for the 300SE/SEL are outrageous expensive compared to ones for the other 126 models.

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1979 Black on Black, 300CD (sold), 1990 Black 300SE, Silver 1989 Volvo 780, 1988 300CE (vanished by the hands of a girlfriend), 1992 300CE (Rescue).

If you’re still looking - https://sfbay.craigslist.org/eby/cto/d/mercedes-300-sel/6567139009.html

Sixto
98 E320s sedan and wagon