Newer MB diesels versus the glorious 123?

I currently have one... I love it! 95 E300D.

The engine in post 123/126 models is not purely mechanical there's some electronics to it and I've seen people pull their hair out over oens that don't work right. Other than that they're about the same.

The 123 chassis and its Turbodiesel power unit is about as DIY friendly as it can be. Lots were sold so, with patience, one can find one, with relatively low mileage. Don't overlook the 300SD which have same power train but somewhat larger size. The old all iron 617 motor is very tough and durable.

The later models have more power from increasing sophistication - and, as with any sophistication, complication and lessened durability. They're still good cars (except the 3.5L diesel) but if you want reliable, and easy DIY the 300D, 300SD are top picks, a 300SDL is a step newer if you can find one without a zillion miles.

I've owned a '80 300SD since new; its now at 110K miles - so be patient, such old cars exist and do occasionally come to market.

I have seen a 95 E300D at the local MB mechanic in Gainesville with 366K miles. I have also seen a 98 E300TD with ~270K miles. The owners said they have had few problems with these 4V/cylinder diesels. These newer engines appear to be just as durable as the older 123's. Not sure about the recent CDI's.

Raj

The FIVE cylinder diesels were all iron, the SIX cylinder (300SDL, 350SDL) engines had aluminum heads (overheat once and they're done) and were subject to stretching con-rods because they were designed for higher cetani Europran fuel.

Avoid the 6's. The fives will last nearly forever.

I'm getting confused now. I have an OM602 5 cylinder 2.5 liter diesel in a '87 w124 250D. Is that an aluminium or an iron head?

Ximinez

OK, the old 617 5 cylinder 3.0L engines installed in the 123 chassis and the 126 chassis through 1985 MY are all iron motors.

Starting in 1986 the 3.0L diesel became a six cylinder with an iron block and alloy head. I believe the 2.5 L five is also that combination (hold a magnet against the head to know for sure).

The newest 3.0L V-6 is an all alloy engine with enough controls to look like a gasoline motor. Remarkable power but not something for a DIY owner, IMHO. And, to come back to the original question of relative durability and complexity, that's the where the trail from the early 617 engines led - to this newest V-6. So one can pick his entry point in the technological progression and enjoy its relative benefits, or difficulties. That WAS the question.

In my experience, the W123 was the pinnacle of Mercedes durability before the bean counters had a hand in design process. And while all of the Diesel engines put into the W123 have exhibited incredible durability, the OM617A turbo five is easily the best. 240Ds also have their fans, as you could get these cars without potentially troublesome items like the automatic transmission, automatic climate control, and power windows. As someone else pointed out, the W126

300SD seems to be overlooked by many people. They offer very similar performance and economy to the 300D Turbo, but with added refinement and space. The only downside is that many have power seats that might become troublesome.

A few thoughts on the OM617A

With an OM617A it's important to drive them hard occasionally, as one that has been pussy footed around for decades is likely to be very clogged up. Find a nice clear road, and keep it floored from a standstill until it shifts up to fourth. After letting it cool down with some gentler driving, repeat the process until you no longer get huge clouds of black smoke out the back. A little smoke is unavoidable if you floor it, but not too much. Check that the valves are adjusted properly, that the injectors are clear, both fuel filters are new, and that the vent line thingy which runs from the back of the block isn't clogged with goo. If you have a late car with the KKK turbo, check the boost level. The adjuster spring tends to weaken with age lowering boost. Unfortunately you can't adjust the Garrett turbo easily.

Once you get the OM617A running as intended, you'll shocked by how quick this car can be.

What power should the OM617A turbo engine produce in good shape and typical economy when touring ? Thanks, Nick

120HP, 118mph top speed. 25-30+ mpg. I got 33mpg once on a 20 hour drive at slower speeds in a freshly tuned motor.

The OM601 is 4 cyl. 2.2L non-turbo engine, only available in US market for MY84/85 on W201/190D (I think Europe had it a year earlier but I have not confirmed that). OM602 is 5 cyl. 2.5L, with or without turbo, used in W124 and later W201. OM603 is 6 cyl. 3.0L (or 3.5L) turbo engine (in W124 and W126). They all have aluminum head with iron block.

OM617 is used in W123 and early W126, pure mechanical engine, very simple to maintain.

MB started to put some electronic engine control since mid-80s, for example, OM603, though it still runs when the control is not functioning right.

I am not sure about the later diesels (OM604, OM605, OM606). But all cars (not just MB) now have more computers so they are def> I'm getting confused now. I have an OM602 5 cylinder 2.5 liter diesel in

So let me make sure I have this straight. THIS IS NOT NECESSARILY HOW IT IS. THIS IS MORE OF A QUESTION. please correct me on the points where I am off.

The W123, which is up through 85 is solid. Starting in 86 there is the W124. In 87 they put the 6 cylinder into both the 300D and 300SD, and it is strong, but it's aluminum head makes it prone to head gasket failure and head problems if it ever overheats.

Then starting in 88 the 300D went back to a 5 cylinder engine. (Was this an aluminum head or iron?)

The 300SD stayed with the aluminum head 6 through the end of the run(and is not as bulletproof because of it.)

I have read too many reviews of 96 and on cars that effectively say that it was a step backwards.

I guess what I am really after is whether or not an 88 to 95 300D has a reliable engine. I really like the looks of that generation, and how they are less prone to rust than the W123, but I can sacrifice looks and find a non rust W123 if the W124 is prone to head damage from overheating or is for some reason less reliable.

Thank you all for your knowledge, Bill

Wan-n> The OM601 is 4 cyl. 2.2L non-turbo engine, only available in US market

I wouldn't worry about head damage. My friend has his 86 300SDL and drove it to 300,000 miles with no head job. It is still running.

Sample of one. I know enough people that have had cracked heads from overheating once, and the "stretch rod/oil consumption" problem that I'd never touch one. I don't buy these cars to gamble and hope I got one of the good ones.

Actually he recently got another one second hand... 210,000 miles. My car also has 205,000 miles.