Keimar

Possibly the auxilliary heater exhaust?

Is there a corresponding dramatic improvement in fuel efficiency?  And at what mileage?

That happened on my 2.5 CRD - and was soon followed by clouds of black smoke: a ring failure sucked and combusted oil.

A recon job, but no complaints as the engine had covered 320,000 miles. Same engine in its second life has added 110,000 miles, so far so good.

I believe the VM was originally a marine diesel, so happy to chug at 2000 - 2500 revs (60 - 70mph) all day long and give >44mpg (although Chrysler odometer not the most accurate so probably closer to 40).

K