My son drove my 1988 245dl wagon home from school one night with the needle in the red the whole time.I learned this after some interrogation. It has not run right since. It was stalling and backfiring and everything.I Fixed the radiator but now there is small leaks of anti freeze and a brownish oil type residue on the driveway there are no discernable leaks in the hoses and it does not overheat I also changed the thermostat. I also cleaned the airmass indicator thing.I changed plugs and distributor cap yesterday and noticed one of the plug wires looks bad but didn't change it. today the kid drove the car and said it smoked up the whole neighborhood and only went twenty five and backfired the whole time.Could a bad plugwire cause that much smoke from an unfiring cylinderr, do you think he warped the head ? new engine or new headgasket? 178,00 miles?