You might also want to check your oxygen sensors as well as the catalytic converter and your gas-air mixture as well. Grey smoke is usually a rich mixture smoke, however the amount you described doesn't seem to fit that as much as an exhaust or oxygen sensor problem. But its still good to check.
Currently I have a 96 Maxima with 140k miles that emits white smoke. Which is most likely the head gasket.
Joe
Thursday, July 19th, 2007 AT 10:20 PM