My 86 740 Turbo has been leaking oil. I imagine that the seals need to be replaced with 180k on it. I made an appointment to have it fixed. I had been adding oil 10w 40 when it was needed. Anyway, my girlfriend was using the car for work. I instructed her to add oil if it was needed. She put 15w 45 in it. This is a common diesel fuel. My car is not a diesel. She drove it about a mile and white smoke came from the muffler very heavily. It also lost power. She pulled over. I went to the car and added two quarts of 10w 40 oil. The car hesitated to start. It let out a large puff of white smoke. It then idled fine. But some white smoke was coming out of the muffer. I did not drive it as AAA towed it to my mechanic. I have heard several troubleshoots: cracked engine block, blown turbo, piston, gasket, or bad oil. Someone please tell me that it might be so bad.