Thank you. I've always seen stale air mentioned and wondered, but never got around to looking up the difference. Appreciate the video and thorough description.

I like the term 'dirty air' better. With those, you get the air that was already used to cool the engine blown straight into the cabin.

On these early stale-air systems, most of the exhaust pipe -- the portion that extends back out of the junction box and that runs under the cylinder head to join the muffler connection at the rear -- is exposed. What are people so "worried" or "concerned" about? If that portion of the pipe that is exposed to road salt and all the elements and hazards is still sound, it is doubtful that the portion within the junction box, which is well protected, would be in worse condition. Just use your brain and keep an eye on the condition of the components. As described, the late stale-air set-up differs in that the lower channel encloses also that portion of the pipe that runs below the cylinder head so that its heat is no longer lost to the open air, but is also contributed to the hot air in the system. Theoretically, this could increase the area of pipe that potentially could leak CO into the heating air if it were somehow compromised -- but again, its being protected and enclosed within the sheet metal is an advantage. Anyone familiar with these units will confirm that it is the exposed portions of the exhaust pipes that are usually further deteriorated by exposure to the elements in comparison with the portions protected within the sheet metal. Long story short -- there is nothing wrong with the Volkswagen heater. On the contrary. It's just that, like a lot of other things on the VW, it's a different system from what North Americans are used to. The only obvious hazard I could spot in these videos was the usual fire hazard "improvement" of the 50¢ plastic in-line fuel filter installed between the pump and the carburetor inside the engine compartment. These are Made-in-China car fires looking for a place to happen -- don't let it happen to you. All VW fuel pumps already come with a safe, built-in filter that won't crack and spray raw gas all over your engine compartment. Keeping a vent window open slightly is necessary on early cars, not as a measure against CO poisoning, but simply to vent the air being forced into the car when the heater is on -- otherwise you're trying to force the hot air into a sealed space. Later model cars would feature "flow-through" ventilation so that the poor, worried babies didn't have to crack a vent window and thus risk getting a chill on their fat little baby knuckles.

Great info mike!!

Finally,...now I know the difference! Thanks!

I'm not familiar with the stale air system, but the heater boxes look like a much better system.

Biggest carbon monoxide worry are the tips of the heater box. Change them out.

Nice video

I'm old and now even in my 2018 car I drive with drivers windows cracked a little.

Hey Mike, quick question. I bought my bug a few months a go. It's a 74. When I first got it the heater worked but would stink the cabin up like crazy. I just replaced the fresh air hoses and I'm no longer getting exhaust smell in the cabin. But now I'm getting hardly any air flow. Any idea what the cause might be?