After 2 years of work....I've completed my '72 restoration...but one thing has me stymied.

I have an oil bath air filter... (pictured) and it has 2 air input points... one is a plastic goose neck and the other is a hose connection controlled by a vacuum system. The mysterious hose I think is supposed to run over to a connection point added to the engine tin...into a "hot air riser". I have no such connection point. I thought my motor was the original 1.7.... which I've now rebuilt into a 2056. I do not have a hot air riser tube.

The only place I've ever spotted a 72 with this type of a air cleaner is on a YouTube video of an original 72. https://youtu.be/w-c6Deg3fBU?si=FPjt3Fhg0lqMsaad Spotted at around 11:20 of this video. The video doesn't show where this hose terminates... but I assume into the mysterious "Hot Air Riser".

I also see in the PET diagrams they show this tube which would bolt to the engine tin behind the cylinder one location. I see a few ebay listings for this tube... but I've never seen it on any of the engines I've looked at.

Does anyone have insight into a hot air riser system.... that bolts to the engine tin behind cylinder one? I don't really think I need it... as this is really a summer only car... but I hate having this unknown empty input point on my air cleaner staring me in the face every time I pop the engine lid.

You dont need it. You could swap the air filter for one that doesn't have the extra intake or just not worry about it.

I personally swapped mine for the '73 paper filter setup but there are oil baths without this as well.

for the snorkle to work you need a specific piece (or pieces) of tin
#2 has a specific cutout #32 & 21 that allow it to vent hot air from the back of the cylinder to the air cleaner.

BTW I have the entire kit freshly powder coated FS

I have never seen that before. I have to go crawl under the car now. Thank you Rich!

After a little more research I’m thinking now I have a 73 motor (now just the case ). My engine serial number is EA 082653…which I read is a 73 series code. My car is a June ‘72 car, so it could be a mid year parts swap too. It was definitely a 1.7… but this would explain the mismatch on the air filter and engine tin. Surprise! My engine tin was crushed inward on the drivers side… which I presumed was caused by someone picking up the engine with a chain wrapped around it… which is typical of most junk yard treatment of spare engines.

It’s also a tail shift so perhaps the engine was just swapped. I rebuilt the engine as part of my total car rebuild project… as the compression test was quite low and had a huge range of values across the cylinder's.

Maybe it’s time to look for a 73 air cleaner after all.

Thanks for your help!

the stove pipe preheat for intake air is a funny one.

i know why the carb engined aircooled VWs had it.
carbies don't have a way to sense intake air temp.
so the old preheat tubes used to help with smooth idle. esp if ambient air temps were low. my old twin carb squareback had a version of the few different types they installed
if i remember right it was a flap that had a little counter weight.
at idle it would close cold air and open to warm air coming off the heat exchangers if i remember it right. there was a pipe ran down there. then when you opened the throttle the weight would be overcome and you only got ambient (cold air) intake.

but not really sure why they put them on EFI cars.
electronic fuel injection has intake air temp sensor that feeds into the ECU and control all that. At least L-Jet does.

Perhaps D-Jet never had temp sensor for intake air? dunno much about D-Jet in detail.

The 1972 diagram looks a lot like the oil bath on my ‘72 Type 1 1600

Click to view attachment

not sure either. to my knowledge that setup was never installed on a T2

I found a 73 air cleaner on EBay and ordered it. Looks original.

My 72 intake had been painted blue… yuk. The PO must of loved blue… there were a bunch of parts painted ford engine blue. And someone spray a coat of single stage silver in the engine bay over everything else. What a mess. All the wiring… hoses… lots and lots of time cooking and cleaning parts in my ultra sonic cleaner.

The DJet does have an air temp sensor in the intake Plenum. There is another temp sensor which sits on top of the engine… And of course a head temp sensor. I installed a 123 distributor and it also senses and reports temp.

yes, they are a curiosity those preheat pipes.
the dim recesses of my memory tell me that the squarebacks (or type 3 generally) had that pre heat hook up to the aircleaner intake on the later type 3 only. the ones that had the longer nose update from whenever is was 1970 i think. i seem to remember the older type 3 did not have it or the hookup to the heat exchanger or wherever it was that it went down under or near the fan.
and these were all carb cars down here in aus. very rare to have EFI type down here.

it seemed to be something VW were doing around that time for some reason.

and they must have decided the type 4 engine needed it too. at least for a short period of time. can't think why it would be when you have EFI. because i don't think the first 914/4s had it. whatever it was it was a blip on the radar.

i think the later beetles down here like the super beetles (which were carb here) also had that heat pipe additional stuff to the air cleaner too. and it can't be about winter conditions down here because............we don't have a winter really. its a slightly cooler 3 month period down here with a quaint european name.

I just assumed you were getting the same cars that the Brits got.

not quite
we got into emission controls earlier than brits and europeans.
pretty much as per the japanese were the aussies.
we followed you guys with your standards but trailed behind a few years.
our govt (and aus generally) was losing its love of the mother country and going USA after WW2.
in fact emssions standards were one of the things that killed off european car imports into australia in the second half of the 70s. the japanese were on top of all that - we matched their domestic market standards which were kind of in lock step behind america but with a time delay. america led the way. europe really dragged its feet.
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but i think i might have figured out what was going on with the stove pipe for one year.
VW were using it as a stop gap emission control.
quick scan of the parts lists shows they updated the ECU with the EA engines by the looks of it. probably the ECU got a more sophisticated bit of circuitry in there to react to the inputs of intake air sensor. for interim year in 72 looks like the kept older ECU and helped its circuitry out by controlling intake air temp between certain temp limits.

probably if it fell outside those temp limits it suddenly got real dirty on emissions.
each year from 70 the emission limits on certain gases got stricter and stricter on a step by step basis.

they were not using the stove pipe on aussie VWs for emissions i don't think, more for making them idle smooth at the lights and then get a more dense charge at full throttle with cold air. emissions standards lagged too much here (4-5 years) for it to have been a factor on the carby air cooleds in 70-73 in aus.

i reckon VW invented it as an improvement in power and smoothness for the carby cars and then flipped it into action on USA type 4 (or maybe even type 3) EFI as a stop gap interim measure before they updated ECUs to be more sophisticated. that would be my guess.

mr b ( @JeffBowlsby ) who knows his D Jets backwards no doubt has the answer to the reason for the stovepipe to critique my guess.