1980 250t common 123 motor problems?

[72-250c]

is there any knowledge of common problems on the 123 motor? i have a 1980 250t grey market gas wagon that is blowing smoke. i suspect it is a head gasket. there is no exhaust gases found in the rad. there is no evidence of coolant in the oil. compression check seems ok. loosing some coolant but not oil. i am going to pop the head off to take a look. i was wondering if anyone knows of any common problems associated with the 123 motor head that i should be addressing. the head will be farmed out to the head and block shop when it comes off.

any advice?

[t walgamuth]

What color is the smoke? Does it subside after the car warms up?

Are your hoses getting hard after the car runs? Is there bubbles in the coolant after running?

A compression test might also reveal a low cylinder or two. Pulling the head is a lot of work....I'd wanna be a bit more sure than you sound.

[72-250c]

whiteish smoke, block tester shows no exhaust gas in rad but maybe i am not using the tester properly. smoke gets worse after warming up. hoses are stiff when warm. i am think head gasket, but does anyone know if there are common head problems with the 123 motor?

[t walgamuth]

not really. if it is a small leak sometimes the coolant seeps in on shut down and blows a bit of steam on start up then subsides.

[Mark DiSilvestro]

Only thing I've heard about the M123 2.5 engine is that with a single-row chain and only four main bearings, it may not be as robust as the old 2.8 /2.5 sixes.
What does the 'smoke' smell like? If it's burning oil, there will be a definite smokey smell, while burning antifreeze has a strong, sweetish odor.

Happy Motoring, Mark

[Xlimodriver]

Blue smoke when at idle = valve seals.

[cth350]

The M123 is the next iteration after the M130. Shares lots of ideas in common. No clue on specifics like the fragility of the head gasket or the quality of the crank support. I don't think the lower end would be any less robust than the M130. Mercedes usually doesn't go backwards like that (well in the 70s they didn't).

The solex carb is sized differently from the one on the M110 should that ever be an issue for you.

-CTH

[have mercy]

Look at plug's if they are not full of oil and, look tan , it a valve seal problem , most of the time it come's from not adj. then the guilds where out. I had a 123 ---110 engine number 1 ran so hot it would eat the center of plug. At night it looked wild watching spark plug wire jump up and down with fire shouting out. It would only take 2 week to go throught 1.

[Mark DiSilvestro]

Originally Posted by cth350

The M123 is the next iteration after the M130. Shares lots of ideas in common. No clue on specifics like the fragility of the head gasket or the quality of the crank support. I don't think the lower end would be any less robust than the M130. Mercedes usually doesn't go backwards like that (well in the 70s they didn't).

The solex carb is sized differently from the one on the M110 should that ever be an issue for you.

-CTH

My info on the M123 engine came from a British magazine article ('Popular Classic' I think) on buying a W123 car. The author claimed the M123 single-cam six was less desireable than the others due to having fewer main bearings and a single-row chain.

Happy Motoring, Mark

[Takernz_30]

the M110 engine is the DOHC version of M123 engine, same block but enlarged to 2.8, 7 main bearings and double timing chains thus making it robust engine despite stronger at hi revs (4000 rpm above). Maybe this(M110) is the answer of M123's problems.

[Mark DiSilvestro]

Originally Posted by Takernz_30

the M110 engine is the DOHC version of M123 engine, same block but enlarged to 2.8, 7 main bearings and double timing chains thus making it robust engine despite stronger at hi revs (4000 rpm above). Maybe this(M110) is the answer of M123's problems.

More likely, the M110, introduced in 1971, is a DOHC developement of the SOHC M130 six, as the M123 2.5 six wasn't introduced until a few years later.

Quote from W. Robert Nitske's book
MERCEDES BENZ Production Models Book 1846-1995
"The 250 model was the third of the newly introduced cars at the Geneva Auto Show in 1976,
having the identical 123 style body as the 200 and 230 models with the round headlights.
But the engine for this W123 model style was a newly designed 2.5 six-cylinder unit developing 129(DIN) horsepower at 5,500 revolutions per minute. It was a high performance engine built for economical operation. The four-bearing crankshaft had nine counterweights for improved balance,"

Happy Motoring, Mark