I will be keeping an eye on this thread as the other halfs 1989 300d w124 (Uk non turbo, 603) does this.

Yes there is the usual smoke seen at night if the throttle is floored but this occurs on a constant cruise condition.

When I picked my 1990 300d up I followed her back on the 50 mile drive and I noticed her car would puff some smoke out at what seemed like regular intervals,not much but it could be seen and smelt (burning oil/blue tinged smoke)

Her car does not smoke as you would expect as if the rings or bores or valve stem seals were bad,it just seems to 'occur' every so often.

We were away the weekend and covered about 400 miles and I only noticed it the once and this was at cruising speed of 80 mph and around just under 4k revs.

The glow plug light does seem to come on every now and then which I know points to a bad pug but the car starts and runs faultless despite up to minus 8 deg C temperatures overnight.

I have wondered if when the light for the plugs comes on if the glow plugs are on ? during driving on a warm engine,or maybe a build up of oil in the engine breathers gets taken in to the cylinders and is burnt.

I did check the oil level today and she has got it quite high,probably about a litre and a half more than it should have .