Maintenance on a Higher Mileage '90 300SE Engine
 

I have a 1990 300SE with 185K and the engine has never been opened since new.
Should I have any preventative maintenance done? How long will the timing chain last?
The waterpump and starter and alternator have been recently replace.

How long can I expect an engine to last? It has been properly maintained (oil and MB filter every 3500-4500K), mostly highway driving but driven aggressively.

Thanks,
Dan

For many reasons, the timing chains really never need replacement on the six cylinder engines.

It wouldn't hurt to check for timing chain stretch and to replace the chain tensioner.

As far as engine lasting, it seems that the valve seals and valve guides should be replaced every 250,000 miles or so. The bottom end of these engines allegedly never wear out.

As far as maintenance, I always tell people to not forgot two items, which are a critical part of your car's maintenance, but often get overlooked because they are the only maintenance items performed in time, not miles:

1. Brake Fluid - required replacement interval - every two years.
2. Radiator Coolant - Required replacement interval - every three years.

There is no need to replace the valve guides or seals unless the engine is using oil. They are not a preventive maintenance item.

These engines have a ratcheting tensioner, so it does not need to be replaced on a periodic basis. The ratcheting tensioner is the saving grace for the chain itself, so you do not need to replace the chain until the engine comes apart for some other reason.

My M103 engine now has 240,000 miles and is going very strong. With frequent oil changes, and a little luck, the sky is the mileage limit for these engines.

Good luck,

Ok Thanks for the input. Looks like the only thing that will force me to get rid of it will be rust.
Dan