1970 Mercedes-Benz 300 SEL 6.3 problems



Thank you for considering my old car issue on my 1970 300 SEL 6.3

I am the 2nd owner and have had the car since 1986. It has 155,000 miles. I had a broke down last year when the car began running erratically and did not seem to get gas. I was told the problem was with the fuel pump and the mechanic replaced it with a rebuilt one. That one needed to be returned as it did not push enough gas. The replacement one was within the acceptable range; but low. Ever since I’ve had the following problems:

1- In cold weather it is very difficult to get it to start; requiring many, many ignition engagements to finally turn-over. When it does start it seems to respond well to the gas pedal requests for fuel and power.
2- However, once running, driven up to normal temp., and then turned off, the car is very difficult to get re-started…………………. Again, requiring many ignition engagements or sometimes, it needs to left for a while as though it was flooded with gas. Then, after time passes, it will re-start ……………… easily if warm weather, more difficulty if cold.

The mechanic can’t figure it out (he is not an antique Mercedes Mechanic). He has told me the vehicle fuel injection pump system does not appear to be holding oil. However, once running it runs strong…….?

He also said that he believed the fuel system has different sensors (3 I believe he said), and that they may not be functioning properly and communicating with the system.

Any help or insight you could provide would be greatly appreciated. I don’t want to simply give the vehicle to a “antique Mercedes specialist” and have a very expensive experience that doesn’t address the problem.

The Mercedes dealerships in my area will not work on older Mercedes…………….?

I was told when I bought it from the original Mercedes dealership that imported the car to the US for the original owner that it was built to be Germany’s response to the Detroit “Muscle Cars”………………. The Mercedes engineers put the Limo engine in the sedan body. It supposedly was the fastest Mercedes ever produced (at that time) and was called “The Autobahn Cruiser”. I also was told that the later models with the 6.9 engine was not as fast as the 6.3.


I am sorry to tell you that the antique Mercedes specialist is exactly what you need if you want this car to run right. Given a 40 year career length for a mechanic, most who’ve worked on these have retired EXCEPT the specialist. The mechanical fuel injection system on your Benz is as foreign as a carburetor to most of the mechanics in the field today. Accept the fact that is is a 48 year old antique that needs service accordingly.