'72-'79 Bus Recirculating Air Modification for More Heat

'72-'79 Bus Recirculating Air Modification for More Heat

by John Anderson


First things first, the stock system must be made to be 100% airtight and restored to "new" condition. The buses featuring steel main pipes likely won't be at this point, but even those with the double layer foil paper pipes are likely to have the Y at the rear, and more importantly the distribution box under the midsection, rusted out. Your choices here are ones of ingenuity, the Y is tack welded to the crossmember on each side and riveted under the rear seat in 2 locations, the distribution box is tacked to the crossmember on each side. There are plenty of warm climate buses who still have these in good shape, if you can find one you are lucky.

I note now that to really see how bad they are you have to peel back the insulation, which is likely causing them to rust out anyway as it holds moisture and salt, but it may also be asbestos. There isn't an iota of the asbestos you will be exposed to. The bulk of the asbestos from the flex tubes, flex tube seals, and particularly the insulating mats on the bottom of some exchangers, should it become liberated, would end up residing in the corrugations of the main and distribution tubes. This residue, along with road dust, is probably the bulk of what some people notice builds up in these tubes. This you can clean out. Take precautions as you see fit.

So your Y and your distribution box are rusted out? Your options: find replacements or ingenuity. As mentioned, the air directly out of exchangers is HOT, but I did use a plastic Y at that time to replace just the tip of the Y section. It was a modified piece from the front distribution ducts of a bus, connected with flexible tubing. McMaster-Carr sells a Y adapter (5398k19 old pn) for car garage exhaust that is 2-2.5" and 2.5-3" out, made of cast aluminum for $20 that would work nicely. They also sell a number of fiberglass, silicone impregnated, wire coil hoses that are good to 550F or above which I have used extensively in direct contact with exchangers and exhaust components to replace missing parts on Vanagon systems. It's good stuff, but costs $6-$10/ft, so you need to plan carefully.

You manifold distribution box choices are: If they are really bad, one solution (if you can't find a replacment) is to pipe it straight ahead with tin pipe and forget the rear. If your box isn't too bad, weld patches. Check the condition of all these parts, disassemble them and blow out all the hoses. I'm a bit leery here, not for asbestos but because it is very hard to get the paper off without destroying the ends and the bent pieces for the rear are very fragile and apt to split. There are NO good replacements for these pieces that are inexpensive. Nothing I've found in the aftermarket is insulated like the factory parts so make your decisions. If my manifold and Y were solid and all the joints look tight, I wouldn't touch a thing.

We must also be sure that both exchangers, flapper valves, and flex pipes are solid and that all the joints between all the pieces are tight. These are NEVER put back together right by casual mechanics. The thing I hate the most about air cooled vans is dealing with the heater stuff when installing an engine. It can take HOURS to get everything to fit right on a '73-'83 vintage van! The aftermarket (Dansk) boxes never fit well to all the little connector pipes and the pipes are usually rusted. The front joints from heater box to riser pipe are particularly bad, especially if they are the oval (not round) type. They differ by year and exhaust.

The rear joint where heater box meets the fanshroud should have 1 way flapper valves and should be gasketed with molded asbestos gaskets. Those gaskets are impossible to keep intact and are usually gone. I'm pretty sure they're no longer available. Just using silicone at that joint doesn't help because the gasket spaces things and makes the flappers work. In it's place, I use a 3M product putty that is made to firestop conduit passages through walls etc. 1/8" silicone rubber sheet would work nicely since the input end of the exchanger isn't likely so hot. For the other joints on the front of the exchanger, the exchanger to flapper risers, etc, use high temp silicone. Use hose clamps or restoration of the origional welded on clamps to make all those joints PERFECT.

OEM (original equipment manufacturer) bus flapper boxes have asbestos seals, replacement boxes lack the seals. Vanagon boxes have silicone rubber seals, but they aren't compatible with buses. You want that flapper not to leak when it is in the heat forward position blocking the vent, so repair as necessary. The seals to the flex tubes on the bus are asbestos, the Vanagon has silicone rubber (red or black). These do fit buses (the ones off the straight tube of Vanagons) and are a great thing to buy or scrounge in a yard. Beyond not being asbestos they simply work 100% better and are easier to get together and seal perfectly. You will have to deal with and remove the old ones. Take precautions as you see fit.

Cables are about the only thing left in the stock system. They have to work or you can just wire the flappers open to the cable brackets (though cables are still available and fairly cheap, ~$15). You can get some adjustment out of your existing ones (they tend to stretch) if you can get the barrel nuts apart and working. Replacing these and coating everything with antiseize on reinstallation is a must. Now is a good time to remove and repack your CV joints. Access to this entire area is greatly improved by the removal of the axles. If you are cheap and ingenious you can cut the end off a stretched cable and fabricate a crimped end on, or use one of those accelerator cable repair kits to shorten the cable.

Now your original system should be solid all the way from booster fan to front vents and leak free. The cable system shoulc fully open the flappers (disable the cable that ducts to the rear if you remove manifold box.) The bus should now heat better than it ever did. With one or 2 occupants it might be liveable on a good trip down to about a 30-40 F day. It might give you around 50F inside at the front and keep the windshield clean under those conditions.

I was driving alone every day 70 miles 2 ways in subfreezing weather. The temp rise in the front vents with the system in this restored shape under these conditions was somewhere like 15-20F above ambient in the vent (not in the cab). With one person in the bus I had to layer very heavy clothes, coat, gloves, and a clear windshield was not a given and I probably was hypothermic when I got to work. Adding a recirculating system helps overcome this problem.


On the stock electric fan there is just enough of a lip on the intake to attach a close fitting piece of hose. I don't think bug/bus hose is big enough, so I used air intake hose from the parts store. I glued it on with silicone and attached with the narrow German style hose clamp or band clamp. It will stay if not disturbed since there is likely a slight negative pressure in the fan suction. Now you must direct this air and to accomplish that, you *must* cut a hole in your bus. You want air out of the interior to recirculate, ideally from low in the rear which is perfectly where the coldest interior air (but still warmer than outside) will be.

On my '76 bus, the solution was as follows:

I had a bunch of scrap front air vents out of front dashes and the vents that on a passenger bus are fed by the tubes on the front doors. This little plastic vent looks nice and fits into a little aluminum collar that snaps though sheet metal. I carefully used an appropriate hole saw to cut a hole on the right rear interior pillar for the vent. BUT the gas filler is back there, and the overflow system and gravity locks and whatnot are back there (i.e. lots of gas available to drill into, be carefull when choosing a location).

Now the size of the fan intake and this vent thing weren't the same, so I fabbed a little aluminum reducer for the vent to get down to the hose size and plumbed it all together using silicone at the joint though the sheet metal. I removed the flapper from the plastic part of the vent (snaps out), cut a neat hole in the black trim panel and snapped the vent though into its housing. It all looked quite nice and basically stock. It occurs to me on a Westfalia you could probably use the stock rear underseat vent plumbed elaborately up through the tin somewhere, however, you would lose a lot of heat from the air you were pulling. Likewise you could take route similar to an engine compartment mounted gasoline heater output vent (though the firewall beside the gas tank and out under the rear seat), but that is pretty involved with the engine in situ. Up on the pillar seems to be the best option. The floor of the luggage compartment is possible, but then it gets covered up.

Benefits: On the 70 mile daily trip, temps were raised quite a bit as the trip went on. I think that I was looking about 30 minutes into the trip at heat 30+F higher than ambient coming out the vents, but results may have been better. This bus also featured a nice 1" layer of fiberglass insulation above the headliner and similar behind all door panels, another real important element in heating a bus. I do know I could then comfortably drive on a 15-20F day without my heavy coat and heavy gloves and have a nice clear windshield at all times and not die on a hour and a half trip.

For '68-'71 buses your solution is quite simple: buy one of those bug recirculating air kits and plumb them with seperate fans for each side into the interior. For Vanagons without the electric fan but with the alternator mounted fan this should be possible as well. Just plumb into the intake of the alternator fan.

The funny thing about all of this is that my '76 bus handled so much better in the snow compared to my '85 Vanagon that I preferred to drive it without heat. A bus is really predictable and "tossable" in the snow, a Vanagon is sort of lethargic and unpredictable. I often plowed along though 12+ inches of uncleared interstate in the morning and would never think twice about hopping into the rutty passing lane to blow pass slow moving vehicles. Good tires and a sensible driver behind the wheel can go anywhere.

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