Hello,

When I had my 1987 300D inspected (prepurchase) by its long-term mechanics (Mitch Carr's in Kensington, MD), they mentioned that it had an engine knock (which it does) that had developed five years ago after the previous owner (or someone who'd borrowed the car, more likely) had filled it up with Regular Unleaded. The car was not driven far--it was towed to the shop, purged of RUG, and refilled with diesel.

After the incident, the car had issues with smoking, which is no longer a problem, and developed an engine knock, which is still around. The shop mentioned it did not seem to be a problem, just a bit loud. I went ahead and purchased the car with only 131K miles a few months ago, but I'd like to work on reducing the knock. (It gets really quiet on Diesel Purge, incidentally, but gets loud again once it's running on pure diesel again.)

What I'm wondering is, what are the effects of gasoline on a Diesel engine? Can this type of incident cause a knock? Does it damage injectors? Has anyone ever encountered a similar problem? What were the damage characteristics, and how did you go about returning the engine to top performance?

Thanks for your help!

--Matt