Auxiliary Heater for PD Engines

Hello,

I have an older Webasto auxiliary heater, model DW50, which uses a built-in fuel tank. This tank is filled while the engine is running, via the fuel return line. I wanted to install this heater in a Passat with a PD engine (ATJ). The Bosch service department told me that this heater cannot be used with a PD engine. Apparently, only heaters with their own fuel line are suitable. However, they could not provide me with a technical explanation.
Can anyone tell me why this shouldn't work? Perhaps someone has already done a similar installation?

Greetings.
Rupert Gschwendtner.

Hello,

Perhaps because the fuel return system in PD (Pump Doser) systems can get quite hot, and this could potentially cause the fuel tank of the auxiliary heater to leak?
Therefore, some PD vehicles also have a fuel cooler installed.

Best regards, Rainer.

hi

I once read somewhere that the pressure in the return line of a pump-injector system is too high.

Best regards,
Eric

Hello,

I don't know how much time you have for tinkering, but maybe it would be an option to create a separate system for this auxiliary heater, i.e., a separate line to the back with its own pump.

It would definitely be cheaper than buying a new heating system.

Best regards,

Jan.

Hello everyone,

Thank you for your information.
Based on your responses, it seems you suspect that installing a DW50 in a PD vehicle might not be good for the heating system.
Could problems with engine performance also be caused by different pressure levels in the fuel system, etc.?

Converting to a separate fuel supply system seems to me to be the safest option.

Greetings.

Rupert Gschwendtner.

In PD systems, the fuel, which can reach temperatures of up to 80-90°C, is mixed with cold, fresh fuel in the return line. This warms the new fuel in winter and cools the hot fuel returning from the engine.
If you now install a SH (presumably a heat exchanger) in the return line that contains a tank of approximately 500ml, the heating system will initially experience significant temperature fluctuations. The return water may no longer be cooled effectively, and there is a risk of a temperature overflow in the fuel system, which could cause the PD (presumably pressure differential) elements to overheat because the warm fuel cannot be transported and cooled quickly enough.

If you have some skill and the necessary materials, install a fuel line with a booster pump from the rear tank towards the front. Never tap into the fuel cooler (usually located on the underside of the vehicle), as it's very difficult to seal properly afterward.

Good luck!

Hello Julian,

Thank you for the detailed information about the fuel system.
I will install a separate fuel line leading away from the tank, as the risks, especially concerning the PD elements, would otherwise be too high.

Greetings.
Rupert.