Okay since i posted this question, i have had a customer partially install to veg system into his early production 2004 jetta PD. I supplied him with a Vegetherm [electric fuel heater from Plantdrive] and a lift pump of which i told him to install so that it pulls both diesel and VO. He did most of the installation himself [yikes ! what a mess] and came to me to redo most of the wiring and plumbing which he messed up. Long story short his car now uses the tank pump when it's on diesel and switched off with no other pump used for VO. Performance hasn't suffered and so i guess we'll see if and how long his tandem pump lasts.
I only did what the customer asked. I also checked out what other installers are doing including the ones in Europe where they have been doing PD s for years now. I told this customer that he is a bit of a guinea pig and is okay with that. His tandem pump is brand new since he somehow sucked raw, unfiltered WVO into it to the point that it completely clogged up and failed.
i would be more worried about the unit injectors than the feed pump... :shock: thick unheated unfiltered veg! :shock: in a PD? :shock: this is good info though... i'm converting a '98 new beetle over and need to install the lift pump. i want a nice reliable solid state pump but i can't seem to find one with the high rating... all i see available is the 4-7.5 psi pumps on ebay... i suppose i could buy two of those and see how that works??? when i had one on my 1.6TD it really makes the pressure, and is very quiet & reliable.