Hallo Ofer, I have to add to the previous answer, that it is very important to see and hear the splashing water from the siphon is working - otherwise you have the risk of getting water into the engine. But you are in the same situation as I was few days ago - looking for something you find new things on the boat -still after 5 years.
We had barnacles on the prop after the winter and the engine reaches only 1100 rmp - 45 minutes diving for cleaning the prop. My first year with propspeed.I found one side of every three blades relative clean and after cleaning the surface of the blades looked good and max. RPM is 2450 .
Whenever I would have a problem with Rpm of the engine I would dive !
With every fuel I take I add Grotamar against diesel-pest. If you think your fuel is contaminated a Grotamar shocktherapy and changing the fuel filter.
Do you know that your VW TDI has a OD2 output to get more diagnosis from the motor.
It is in the box on starboard of the engine with the 3 red led on the top.
You will find OD2 meters in the Internet, I searched for VW TDI OD2.
WOLFGANG WEBER SY Elise Amel 54 #162 Marina Zea Athens
back to work on Monday