Are 603-powered cars reliable?
 

Just what the title says. I've wanted a w124 300D for a long time but what puts me off of them is the potential problems with the 603 engine.

I've read quite a bit about them and while a lot of them reach high miles like 617-powered cars, I've also read about the numerous problems 603 owners encounter, even when they are well maintained.

All things considered, is this a reliable engine?

they are reliable as the 617 provided it is properly taken care of

Mine has 256k and has been my daily driver for six years without major incident. I can't think of anything engine-related I've had personally other than leaks, which happen on 61x engines, too. New lifters and timing chain at 220k, but that wasn't anything that left me stranded or was catastrophic ... it was 'elective surgery.' I've relied on the car to get back and forth from work, the store, everywhere else on a daily basis. Has always started for me and run great for me in temps from -7 to 107.

You're biggest issue with the 603 would probably be the cracked head possibility ... so don't overheat it. That's generally my approach in any car. I don't think that makes it unreliable.

You'll need to define "reliable".

Many of them go 300K without a problem.

However, if yours happens to crack a cylinder head or fracture a timing chain cover, you're not going to agree with the "reliable" statement regarding them.

It's a statistical issue and we don't have the statistics.

Personally, I believe, statistically, that the 617 is going to offer better durability. But, I had one with a cracked cylinder head. Go figure.

I think the 617 is a little more reliable in the long run, perhaps at a lower maintenance cost. They need valve adjustments and such, but have an iron head that usually never has any issues, and the belt drive system is simple V-belts instead of a serpentine with a tensioner and pulleys etc....less to fail. If properly maintained they probably are about the same. The 603 has more "potentially major" issues that could occur....like cracking a head and such. I'd drive either honestly.

The OM603 and OM617 engines have similar over-all reliability. Although the 603 is no more prone to overheating than the 617, the aluminum head of 603 is more likely to crack if the engine is seriously overheated. If the temp gauge starts getting up towards the 120C mark, you need to stop and find out why. Trying to "make it home" is risky. So long as you take care of the cooling system (change the coolant at the appropriate intervals, keep the radiator clean, etc.) the 603 should not overheat. To be fair, it's also possible to overheat a 617 but you have a larger chance of getting away with it.

My mechanic commented to me (when I bought my '87 300D) that the OM603 is a more expensive engine to work on. This may be so and if you have to pay someone to do all your work you will want to keep that in mind. If you can do some of your own work (change glow plugs, serpentine belt, oil changes, etc.) you'll save a lot of money.

Jeremy

Changing the serpentine belt on a 603 is a 15minute job including cleaning up, try that on a 617, ... adjusting the valves is a non-existant job on the 603, ...

I think that the 603 is an excellent engine and if not abused, very reliable. I believe that I've read about two timing-cover failures here since I joined years ago, vacuum-pump failures of 61x and 60x engines are about the same, IP failures about the same, seldom see a bottom-end failure or oil-consumption issue either.

Get a good one and maintain it reasonably well.

the serp belt is easy if you have the special tool, otherwise you never get it off without breaking something

What special tool? You loosen the locking bolt, use the tire wrench handle to take up the tension, pull the bolt, and release the tension. Then it's just a matter of maneuvering the old belt out and the new one in.

Were you thinking of the special tools for removing the fan? Isn't necessary and anyway, you don't need special tools.

Jeremy

Tension is easy but removing the fan without breaking something.

Special tools are made to make jobs easy and on the newer ones(especially 97 and up) special tools are needed otherwise you cannot do the repair.

I've never removed the fan to do a belt on a 124, just snake it around. The '96-up as you likely know is a different engine and body.

I always remove the fan when I do the belt. The belt is easier to install with fan removed.

I've done it both ways on both the OM603 and the OM606NA. Removal of the fan is easier with the special tools, I would imagine, but not having them, I make do without. Changing the belt with the fan removed is so easy we shouldn't be discussing it.

603 hauls butt
617 hauls my butt around

As Jim(from the forum) said to me once.. "not all #14 heads are bad, but all bad heads are #14's"

The belt on the 603 is beyond easy. The 617 has more room under the hood to work.

It occurs to me that the point we perhaps should be making is that a pre-purchase inspection by a trusted mechanic is more important for a car with a 60x engine than one with a 61x engine because of the expensive nature of the things that an unwary buyer (someone like me :o) may miss. Granted that a pre-purchase inspection is a good thing to do on any car, it's critical to 603-engined cars because of the kinds of problems that may be hidden behind the seller's smile.

Given a good bill of health from the mechanic, a 300D Turbo or 300SDL would be a great car. More modern-looking than the older cars, more power yet better fuel economy, more creature comforts.

Jeremy