I brought my issue up as I wonder if my lift pump is up to snuff. I thought it to be similar to Mcsedes' problem. Scanty or no output of the the aux. pump.

Do I (Does he) need to install a pressure gauge on the output of lift pump. Or can we measure the output of the cigar hose?

I have done some research and read that a 1.5l idi Citroen puts out about 17.5liters/hour out of the return line at idle. That is about 300 ml per minute. Certainly not a 3 liter mercedes but it is a data point.

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85 Merc 300D - Unwinding 31 years of wear
86 VW TD
Mahindra Diesel
Iseki Diesel

In 2007 I didn't own a diesel.