Classic/Antique Car Repair: black carbon in tailpipe, tail pipes, black carbon

Question
Roger JM Warrington: I am looking to buy a Volvo, 1994, 850 , turbo. I have NOT driven it, I am going this morning or tomorrow for the test drive and was recommended to email you first. The tailpipe has a build up of black carbon in the tail pipe, I noticed. Black carbon that wipes rather noticeably, maybe 1/10----1/20 of an inch. The owner was not available, BUT please describe if this is a MAJOR...could be trouble type of problem. The asking price is $3500.00...I think it has 1200000 on the odometer. The rest of the car as i looked it over is very clean, well kept up, fairly good tires, no scrapes on the rims, other than the carbon build up I found...I am test driving it today. Any advise on carbon build up and what to do/or watch out for is so appreciated..Thank you..Daniel: 231-690-3973:   dhlandco@aol.com

Answer
Daniel;
Hi  well  the fuel it is burning is one reason , (normal)  and it has some miles on it , I would take it  ==on a hi-way and go about 65 and see if any thing is comming out the tail pipes when driving it, even in town there should be no smoke , at start up only.  but the black suit  is built up from not driving on a long or vast run for a bit if just driven in town it will build up and on the hiway it should blow out clean, as long as you do not see any black smoke comming out when you are driving along, and if you see any white smoke when driving do  not buy the car as it is burning oil.  ok  P.S. if it makes a LOT of knocking I would think about it, some quiet knocking is normal for a diesel and so is the blak in the tail pipe .......