Air cooled heating – explained

This article will help those with an air cooled vehicle from a Split screen through to the early T25. If you bought a water cooled engine, then it does not apply!

Do you own a VW that you cannot use in colder weather without travelling in a big coat, bobble hat, thick socks and blue fingers? It is a great and effective system but with 39 years since they stopped producing the late Bay and nearly 60 years since the introduction of the Split screen, inevitably there will have been a small amount of wear and tear.

In this article, we are going to cover some of the important parts of getting some of the lovely heat from the engine up to the people at the front. That’s you.

Basics

The engine produces heat and a lot of it goes out of the exhaust system. Part of that exhaust system is the “heat exchangers” and that literally means a sleeve around part of the exhaust pipe that heats up the outside air. Once that air is warm it can warm you but it is currently underneath the engine at the back of the vehicle. We need to move it from there up to you without losing much of it.

The process

The big fan above the engine cools the engine (air cooled – the clue is in the name) and there are two big ducts / funnels, one of either side in the engine bay. These go through the metal tray around the engine, underneath, into the heat exchangers and can then enter the heating system. From there, a control flap can be opened to funnel that heat along a 90mm / nearly 4 inch tube along the middle of the vehicle from the gearbox up to the front wheel line. From there is jumps over the front beam in a squashed tube then turns up at the front at the totem pole for those of you with that funny looking piece of metal.

The first place to look – the end game

If you can get heat into the van, you want to keep it there. Windows need to be able to close fully, doors need to close with no draughts, door seals need to be good. Any original flaps, sliders and other ways of getting air into the van need to be able to seal, otherwise that good, warm air will leave very rapidly. these are all visible and easy to track down. Make sure that the roof has similarly no big holes for heat to leave.

Now focus on the insulation. If you have zero insulation in the walls, the heat is going to leave really quickly – not only when you are travelling along but also in the evenings when you are sitting quietly, drinking wine and playing scrabble. Other excitement is available. Remove the wall panels and insulate – that is an article for another day, just don’t use rockwool which absorbs moisture in something that you squash into cavities pressed against metal bodywork. You may as well just drop the whole vehicle in the sea and let the salt water rust your pride and joy!

For evenings, consider curtains which will help insulate too.

Start at the start

That big doghouse fan noted above. Does it turn freely, helping to cool your engine? Ensure all is good in there otherwise you will have a hot engine and cold passengers. From there on both sides are holes about 3 inches / 70mm diameter – check they are not rusted and letting out that precious heat. From there, they warm air goes into stretchy concertina plastic tubes that pass through the tin tray around the engine and underneath. These should be tightly attached to the fan at the top using good jubilee clips – these are inexpensive and will really help.

Now get under the vehicle, safely (disconnect the battery, use axle stands, tie back long hair and loose clothing, your health and safety officer should be standing by and so on). At the bottom of those two concertina tubes they should connect to the heat exchangers, these are boxes on either side of the engine forming part of the exhaust system and do not touch them if the engine is warm. Again, the connection from one to the other should be free or rust, rot and holes and should be sealed well by the jubilee clips.

Then the heat itself

The air from the engine has now flowed underneath the vehicle and has been pushed past the exhaust, getting hot. Both heat exchangers flow the air into a Y shaped tube, curiously called a J tube, although replacement parts may mean this works slightly differently. From there, that lovely hot air enters the tube running along the middle of the vehicle. Once again, the join from the J tube or similar into the middle heating pipe needs to be sealed and not allowing the air out.

That big tube running along the middle of the vehicle needs to be free from holes. Originally from the factory, it is a heavy steel pipe with a jacket around it. that jacket is often missing or otherwise less than perfect. Check it, refit it, replace it. Even a heavy coat of underseal will give you some thermal help as well as reducing the air loss due to holes.

Just in front of the B posts (between the front doors and the sliding door) that tube joins a flattened pip section that jumps over the front beam and up to the front of the vehicle. That can have holes and is tricky to fix. From there you are almost up into the cab area and once inside, there are usually few issues.

Opening the system

The levers on the dashboard that are red are for the warm air. The green or blue ones are for the cool air. Next week, see how to get the red ones operating as they were designed.

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