Now identified as Heat Exchange

[Circoloco]

Hi everyone,
Last weekend we bought our first T25, an air cooled Devon Pop top. It's got a few little niggles we need to sort but we're happy with it
Today I was looking over it and noticed behind the rear wheel arch on the driver's side looked like a tank that had some rust but also looked like it had wet on it? At first I thought it was the fuel tank but looking online I think that's closer to the front? Off my pretty rubbish description does anyone know what it is?
We're new to all this but think we'll be on fast track to learning!
TIA

1981 2.0 Air-cooled Devon Pop Top

[multisi]

Do you mean the rear part of the inner wheel arch in line with the bumper end cap.

[Circoloco]

Yeah I think so, I've been trying to find the post of how to uploads pictures to show you but I can't find that now
Zooming in on the pic out looks like there's a pipe going in with a clip on
Thanks

[jrt]

Yeah I think so, I've been trying to find the post of how to uploads pictures to show you but I can't find that now
Zooming in on the pic out looks like there's a pipe going in with a clip on
Thanks

viewtopic.php?f=1&t=163556
David.

[Circoloco]

Thanks!
Hope this works
https://imgur.com/gallery/2xvJ0

[petethefeet]

Hi,
That's your heat exchangers around the exhaust, they help to heat the interior of the van, as you don't have a liquid filled cooling system.
The big pipe feeds the cold air around the outside of the hot exhaust heat exchanger so it can be warmed up.
Similar system to the the older T2 van.

Hope that helps

[Circoloco]

Brill, thanks for your help! Looking at the picture do you think it'll need replacing? Thanks!

[petethefeet]

Hi,
Very difficult to judge that from the picture.
The heat exchanger is a thin sheet metal 'box' (the bit you can see) with a heavy metal inner bit that is the actual exhaust pipe. So long as the outer box is in one bit and the exhaust is not blowing it will work to a degree, there is also two air 'valves', one on each side that control the air through the system, these are located at the front end of the big pipe that is on the right of your picture. The outer box tends to rot out and the pipe on the end will rust due to the location under the van.For the system to work well it needs to be in good condition without air leaks etc.
See links below (this shows a Beetle and a T2 but it is similar)

https://www.vwheritage.com/blog/2015/12/29/vw-air-cooled-heater-problems/

http://myweb.tiscali.co.uk/freemefromthishell/vw/T2%20Heating.htm

It might be better if one of the Moderators can move this thread to a more suitable place and possibly rename it so it gets seen by people with better knowledge.

[bigherb]

Brill, thanks for your help! Looking at the picture do you think it'll need replacing? Thanks!

Hard to tell from that picture, does the exhaust system leak, does the heating system work?
But the rocker cover gaskets need replacing to stop the oil leaking onto the heat exchanger.

[Circoloco]

Sorry for the late reply, we've been away for a few days. Thanks for all the info, it's been really useful!
When we bought it the guy said it needs a new silencer, but apart from that not sure. We literally drove home and parked up outside a relatives until we had a bit more time to look.
Thanks for the rocker cover gasket advice too, hopefully that's all we'll need!

[Mine is green]

WRT heat exchanger issues....

I have a CU 2.0 litre engine. Originally when I bought it the heat exchangers had been removed and 'J' tubes installed with the only heating through the petrol fuelled Eberspacher. I managed to get replacement second hand heat exchangers and had them fitted, but my local garage had replaced the fan laden alternator with another that didn't have the fan on. In the process they removed all ducting aswell. They modified the system to use an electrical fan and ducting from a type 2 with electrical control inside the cab. When driving the van clouds of smoke came into the cab (looked as if the van was on fire) and the aluminium from the heat exchangers melted inside the casing! They tell me I have overheated the engine and this is the cause of the problem, but subsequent examination from a neighbour who is an engineer and my own experience as a qualified mechanic (albeit a long time ago) could detect any sign of overheating once the lump was removed and examined. My feeling is that air has to flow through the heat exchangers consistently to stop them reaching the melting point of aluminium and that this is facilitated through either supplying heat to the cab or vented through the 'mushroom' of the heater pods with the alternator fan. I think that the air flow from the electric fan was too low, and some restrictions had been imposed on the system by changing the diameter of the air hoses from 60mm to 50 mm.

The smoke appears to be coming from under a layer of internal heat shielding/insulation in the heat exchangers themselves.

Has anyone had this issue before, I have searched online, but cannot find any references...

[bigherb]

The heat exchangers need air passing through them at all times or they will melt. The original system has the engine driven fan blowing all the time through the exchangers if no heat is needed to the cab, then with the heater pod flaps closed the hot air is exhausted out of a vent in the heater pods.
If you used a bay window electric fan then they are not powerful enough, they are designed only to supplement the engine fan at low engine speeds.
There is someone selling the alternator fan and ducting on ebay at the moment (not me).
https://www.ebay.co.uk/itm/VW-T25-TYPE- ... :rk:9:pf:0

https://www.ebay.co.uk/itm/VW-T25-TYPE- ... rk:10:pf:0

https://www.ebay.co.uk/itm/VW-T25-AIRCO ... rk:12:pf:0

[Mine is green]

Thanks for that, needed the fan...

Is there a supplier that stocks the tubes that connect onto the heat exchangers to deliver the air (opposite end to tubes that connect to the heater pods)?

[bigherb]

Thanks for that, needed the fan...

Is there a supplier that stocks the tubes that connect onto the heat exchangers to deliver the air (opposite end to tubes that connect to the heater pods)?

Not new.
But the part numbers are.
071 256 331 for the left one
070 256 331 right

[Mine is green]

Link: viewtopic.php?f=37&t=164920

Van missing lower tinware that bolts on to the sump, heat exhangers and upper tinware, also the thermostat aswell....

Think I've managed to get the delivery pipes (ebay) , and the lower right tinware (well known VW specialist), but lower left tin and thermostat with bracket seem elusive apart from USA sourced by Awesome Powdercoat.

Apart from getting the original or reproduction version, has anyone tried using a shorter travel bellows-type thermostat and modified the jockey wheel to a lever system?

M.I.G