Originally Posted by Andrew M. Franklin
Whenever I tow ... I detect a mild to moderate odor that smells like burnt-matches phosphorus/sulfur like... Only happens on new trip after trailer has been sitting for a while...
I do not have a specific answer to your situation, but a few observations made while operating my '84 Suburban may help you either solve your problem, or live with it more comfortably.
To point out the obvious, when towing your Airstream, your Burb's motor is working harder which means it is passing more heat through the exhaust system. This extra heat ends up burning off deposits in & on the exhaust system which accumulated during the course of daily driving without your truck being under any significant load. Gone, as you indicated, in five minutes, there is no significant fire hazard associated with the burn-off.
Now, why are you smelling anything since the exhaust system is outside, and you are inside? I don't know for sure, but I have a similar situation, and I think it has something to do with tailgate/aft window seals, and the aerodynamics of the truck. Effectively, the exhaust gas is being pushed into the interior through worn gaskets and/or tailgate misalignment at certain speeds.
I notice a warm-up smell in my truck even quicker when one of my front vent windows is open (in certain postions, the vent window can suck more air out of the interior than it lets in. The depressurized interior can now suck more fumes in from the tailgate).
The exhaust leak path is always there, but you probably only notice a smell when the exhaust is particularly fragrant; In your case, it is the burn-off. In my case, it is unburnt fuel expended since the choke is still full-on.
A possible troubleshooting technique is to duct-tape the output of an electric yard blower to a partially open window, turn it on, and spray liquid soap suds around the tailgate & look for bubbles.