Not sure if we need an overhaul

Just wanted to ask if there is a specific time when u need to overhaul a motor or does it depend on the condition of it?
We have a 1989 300TE with the M103 motor. The car is super smooth throughout the rev range, but today, i was driving behind my dad who was driving the car and he wasnt really pushing it and all this black smoke was coming out...It has 290,000 kms and it drives beautifully..Its just that the black smoke dont look too good thats all... I was wondering if anyone has suggestions?

Thanks
Chris

1989 300TE
1997 C200 Elegance
2000 ML430

[engatwork]

My opinion is that black smoke is an indication of improper fuel/air mixture (running rich) and it may just need a fuel/air mix adjustment. What kind of mpg are you getting? I'll ask this question but I think blue smoke is burning oil - What is the oil consumption like? If it is using more than a qt of oil in 3000 miles it may just need a head job - valve guides and seals. Or maybe you need to add a bottle of Chevron Techron and take the car out on the freeway and run it up to redline a couple/few times and then follow it while driven easy to see if it is still there. How do the plugs look? If it is running good I would not even consider a bottem end rebuild but if you pull the head I would recommend changing the timing chain, tensioner and guides.

Jim is right on with his black smoke/blue smoke explanation.

You need to see to this very soon if you want to avoid that overhaul. A rich condition means that raw fuel is washing the oil off of the cylinder walls. This will lead this engine to an early grave.

Mileage really is no indicator of overhaul time. Some engines need it very soon, while a properly cared for, carefully driven engine, especially an M103 can go hundreds of thousands of miles before the need. Overhaul time is determined strictly by condition.

See to that fuel system soon.

Have a great day,

Thanks very much guys...Not sure what we are going to do. Im going to bring it to an authorised dealer ASAP so we can get it fixed. It uses alot of oil and there are leaks on our garage floor. We love that car and keeping it for as long as we can. Thanks for all your help. Any futher info would help!

Christian

1989 300TE
1997 C200 Elegance
2000 ML430