My old 76 Jeep Wagoneer had a leaky heater core for a while. I was in Idaho during the winter (-20 on occasion) though so I had the heater cranked all the time. There was absolutely no mistaking the smell.....sickly sweet. <img src="/forums/images/graemlins/barf.gif" alt="" />

Put the defrosters on after the truck heats up and see if it fogs up the window. <img src="/forums/images/graemlins/kewl.gif" alt="" />

96 Montero LS 24V DOHC 3.0L.
98 Montero 24v SOHC 3.5L, factory rear locker, Winter/tow package.
63 Jaguar XKE 3.8L FHC
2000 Mercedes-Benz e430
07 fj cruiser