What should you look for in purchasing a Mercedes Benz 300SD or 300SDL?

Answer 1

I have owned about 20 used Mercedes over the years, including several diesels. The 1978-1985 or so 300D (midsize or 123 body) and 300SD (large size or 126 body) 5 cylinder turbodiesel is bulletproof with regular maintenance. 300,000 miles or more with just routine maintenance is not unusual for these engines. The six cylinder turbodiesel used in the 300SDL from 1986-1993 or so (I'm not positive on my years, but what matters here is whether it is a 5 or 6 cylinder) is a completely different engine with a lot of problems both from the trap oxidizer in the exhaust system (kind of like a catalytic converter) clogging/failing and the connecting rods inside the engine, connecting the pistons to the crankshaft, bending over time. This slight bending causes the cylinder bore to become oval shaped, causing excessive oil consumption. Nothing can be done to prevent this, and once it happens, nothing can be done to fix it. I have read that city driven cars might be affected earlier than highway driven cars, due to the higher stresses of stop and go driving. If you research this model online you will find lots of warnings to stay away from the 300SDL. (Google any model of any car you are looking at with "problems" after the model name and you will find lots of useful info about what to look for.) ALL of these 300SDL's will fail eventually, is what I keep reading. Engine replacement is the only option. You can find nice 300SDL's cheap, because knowledgeable buyers stay away from them. A 300SDL replacement engine from Mercedes will have replacement parts that will not fail. If you can document that a 300SDL has truly had a factory engine replacement (or a rebuilt engine from a quality aftermarket supplier, there are several), it should be as good thereafter as a 5 cylinder turbodiesel. As with ANY used Mercedes, you should look for cars with service records from new, some would say preferably dealer maintained, though there are lots of reputable independent shops too. Having a mechanic at either place who has seen the car for years and who can tell you about the car is a bonus. The fewer owners, the better. A 10 year old Mercedes with one or two owners and all the records would be much more desirable than a 5 year old car with no records, in my experience. As with any used car, each successive owner of a car is usually more aloof about maintenance and less able to afford expensive maintenance items or repairs. You should pay for a Carfax check if you have to, though some of these cars may be too old to be covered by Carfax. I have seen great looking cars that have been wrecked or flooded according to Carfax. And remember that you are talking about buying a car that is 25 or more years old. Even though it may be a nice car still, it is going to have age-related problems, leaks and failures and may not be the best choice for a daily driver, though many, many people use them that way still. Parts should be easily available for these older diesels. If you are a do-it-yourselfer, eBay is a great place to find new and used parts.