I have just purchased a 124 body style 300D. It has 131K on the oddometer and seems to have been quite well looked after. It has had the " football" replaced and drives quite well. It is not very fast in fact it seems about as quick as the 84 300D that I presently drive. I have read a little bit about cracking heads and was wondering if that was a mileage related occurance or there was a specific cause, other than overheating. There is a problem with the glow plug system as the car is a little reluctant to start and the warning light seems to have a mind of its own. Any insight with regard to owning this vechile would be gladly accepted.

Welcome to the forum.

The vehicle that you purchased has the OM603 engine with an aluminum head.

The head is adequate for the task at hand, however, any overheating of this head.....even once.....can potentially start a crack that will progress over time.

There is no way to know if the PO has overheated it.......only if the symptoms of a crack start to present themselves. These symptoms include the steady loss of coolant, oil in the cooling system, or pressure in the cooling system after sitting overnight. You can run an engine with a cracked head, however, the problem will worsen with time.

With regard to your starting issues, you have one, or more than one, bad glow plug. When the light has a mind of its own.......sometimes not operating at all.......usually two or more glow plugs are NG.

You can test the resistance of the glow plugs at the glow plug relay. Pull the plug and test each socket (six of them) to ground. The resistance should be between .6 and 1.2 ohms. Any open condition will tell you that the plug needs replacing.

Replacing them on this engine is no fun. You can do it with the manifold in place, but you need a lot of extensions and universals, and a lot of patience. Most folks remove the manifold for that purpose and change all plugs while the manifold is off.

You are aware that the glow plug light is simply a driver's aid, correct? The plugs remain on for approx. 40 seconds, no matter what the light is telling you. On this engine, leaving the plugs glow for 15-20 seconds......even in warmer weather.......will ensure a smooth start without all the kicking and banging that is common to this engine. In colder weather, the entire 40 second cycle should be utilized to assist in a smooth start.