GM-GMC: 96 chevy truck heater, windshield wiper, vent system

Question
HI Harry.
I have a 96 chevy c2500 w/6/5 turbo diesel. It has  no air cond. I noticed lately, (this winter,) that I smell fumes coming in the heater. I thought maybe it was coming in somewhere else but when I put the heat on the dash vents I can smell it coming out. I am pretty sure the exhaust has no leaks. Ever hear of anything like this.?  Where does it get the air for the heat. Thanks in advance             Jim

Answer
Jim,

Unless you have a hole in your dashboard, the fumes have to be coming from your exhaust system and are being drawn in around the base of the windshield (where the windshield wiper linkage is).  This is the location of the air intake for your heating and vent system.

You need to check the exhaust system, from the exhaust manifolds back to the muffler.  The exhaust manifolds are known to crack on GM 6.2/6.5 diesels and the turbocharged engines are worse because of the extra heat.  You may also have a bad gasket at the exhaust to the turbo or at the exhaust manifold to exhaust pipe connections.