2011, seems today getting exhaust smell in the cab. Seems worse when letting off the gas pedal, coasting.. 186k miles. No codes. Gas mileage has dropped on this tank full also. Still runs smooth.
Look for exhaust fume traces at the joints and/ or a crack. Check all the exhaust system bolts. I'd start there. Let us know what you find
Presumably nothing done recently, say head gasket? How about oil fill cap or dipstick: both in place? Any other maintenance? If you’re parking outside: check underneath, maybe someone trying to get the catalytic converter but failed.
Oil change recently, cap tight and dipstick all way in... I have noticed it really happens when let off gas coasting to stop sign. Gas milage dropped to like 38mpg too.
