1998 Chevrolet Silverado • V8 4WD Automatic • 51,480 miles

I have a 1998 Chevy Silverado 4x4 and when I run the heater I get a strong exhaust oder in the cab. I have no exhaust leaks and it does not happen with the AC, just the heater. I get the smell sitting still or moving. Do you have any idea what could be causing this?
November 26, 2010.

Sometimes mold grows inside the HVAC unit and you'll get strange odors. However, if this was your case, you should smell it with a/c on as well.

Sometimes what smells like one kind of odor to you will smell different to someone else.

You may have a slight leak in the heater core or hose that's causing this smell.

Also, I've seen many strange things show up inside of cars. You could try removing the HVAC unit and looking around inside for the source of the smell.

Ernest Clark
Nov 26, 2010.