i've got a 1983 300D turbo, and i'm wondering how hard i should be pushing this thing. i've reached 95 before, but that was going downhill and i quickly backed off (i was more worried about speeding tickets than i was about the car). what's the highest safe cruising speed for an 18 year old diesel engine like this?

on a longer freeway trip i noticed that if i cruised for a while at 80-85mph, the seatbelt light would come on, the tachometer would freak out (no change in actual RPM's), and then would go back to normal if i slowed down. i asked my mechanic about this and he told me that it might just be the car's subtle way of telling me that it doesn't like to cruise at 85mph. but it will occasionally do the seatbelt light thing at much lower speeds, too.

what could be causing this? is there a relation between the higher speed and the electrical oddities?

The electrical gremlins have nothing to do with the car not liking high speed.

These cars were designed for the German Autobahn, albeit not the fastest on there. If everything is in good shape, you can run them all day long as fast as you like to go.

Enjoy,

so you're saying i can routinely cruise at 95 mph with no excessive wear on the engine? the RPM's worry me at anything over 85mph. where should the RPM's be at any given time? 3500? 4000 just doesn't sound healthy to me.

also, what's going on with my tachometer (needle jumping back and forth between 2000 and 6000, with no corresponding change in actual RPM), and why does it only happen when i cruise at 80-85mph?

thanks!

your 83 300D can do 170km/hr. Or about 110MPH. Ive had mine 1 time going the full 110 with the help of a hill. If everything is in tune, valves adjusted, turbo working, and some redline additive in the tank, yours should do 100+ as well.
Your tach is behaving this way because you need a new sending unit, $80. U can replace it yourself. Happy driving!

Yes,

Running it at very high RPM's for extended periods will definitely cause the engine to wear out sooner. Cars in Germany that are constantly driven hard on the autobahn do not last as long as the same car driven at more moderate speeds.

That said, my Euro 240D, with no tach seems to run a zillion RPM at 70 or 80. But I drove the original engine to 380,000 miles before overhaul. more than 90% of those miles were screaming down the highway. I changed oil regularly and took care of it, but drove the heck out of it. After all in a 240D you only have two throttle settings; foot not touching the throttle, and foot holding the throttle to the floor. That's the only way you can get anywhere in one.

Drive it and enjoy,