Its been a while with this. I believe I have gotten to the bottom of my hot start problem.

Turns out after much investigation and some parts changing that the fuel primer pump (PP) is the culprit. This model MB has a high volume primer pump operating in series with the IP. The clear fuel lines I was inspecting along the way were not clear enough to see that there was air making its way to the injection pump. On an occasion I was able to see small bubbles of air in the clear return line from the IP and began tracing back from the IP to determine where the air was getting in.

I worked my way back to the tank. Starting with the CLear bit of fuel line (which was not so clear by the way after 15 years of diesel) connecting the PP to the fuel preheater and the associated rubber lines. Still had air. inspected and changed the hose clamps. Changed fuel tank feed line and cleaned tank prefilter. Still after all this took determined it must be the primer pump cavitating creating air. Changed out pump and it was definately shot.

The air was gone but would be back. This version of PP does not like 100% biodiesel, eihter b/c of the viscosity or the methanol as the pump began to degrade and back came the air entrainment. Note that imediately after the pump change I did notice very very small quantities of air showing up.

I am in search of a cure to keep this car, however my expectations are not good. I have retrofit with a 4psi facet pump (4psi not enough MB spec min 12 at IP) in series with the mechanical PP with decent results until the POS electric facet pump burned up after about 2000 miles. Looking to Bosch for the spec on the pump to see if the seals are all Viton.

Have a 12 to to 14 psi facet pump ion the bench to install a electric pump powered loop to the engine compartment so the fuel is lifted up to the PP. Also in search of VW.

Moral to the story so far as I am concerned is this model MB (W124 w/ 602.962) can not handle bio at the quantities I am running it.

Thanks