Two Tank SVO System

[Legal Eagle]

I am looking into a conversion for my Benz into a two tank system commonly used for SVO (Straight Vegetable Oil). I have several of the necessities figured out by visiting a few sites, although none get into a play by play how-to-do-it explanation.
I plan on running B100 biodiesel in the second tank in winter, or filtered WVO (Waste Vegetable Oil) or a combination of both, and regular dino in the fuel tank for start up and purge, and B100 in both as soon as the weather is warm enough to handle the B100. I make my own and the car loves it.
The questions I have are two:
1) When I set up the SVO tank do I need to vent the cap ?
2) In setting up the two tank system do I need to return the SVO lines to the tank or just loop it back to the pump?
Thaks for any feedback.

[Old300D]

You need to vent the cap. It depends on your design whether you loop it or return it. In my new system, I am going to return to tank because I am running a small tank, and I don't want to deal with bleeding and air bubbles.

[TonyFromWestOz]

Originally Posted by Legal Eagle

I am looking into a conversion for my Benz into a two tank system commonly used for SVO (Straight Vegetable Oil). I have several of the necessities figured out by visiting a few sites, although none get into a play by play how-to-do-it explanation.
I plan on running B100 biodiesel in the second tank in winter, or filtered WVO (Waste Vegetable Oil) or a combination of both, and regular dino in the fuel tank for start up and purge, and B100 in both as soon as the weather is warm enough to handle the B100. I make my own and the car loves it.
The questions I have are two:
1) When I set up the SVO tank do I need to vent the cap ?
2) In setting up the two tank system do I need to return the SVO lines to the tank or just loop it back to the pump?
Thaks for any feedback.

1) Yes.
2) There are many variations on this theme. Some people modify the stock tank ,adding a coolant based heat exchanger to melt the WVO, and use an additional diesel tank in the engine bay or trunk. Others use the added tank for WVO leaving the stock system unaltered.
The choices on looped or return to tank (RTT) depend on several issues:
1. The effectiveness of your WVO heater. If it can maintain WVO at 80'C or better under all driving conditions, with a RTT system, then I recommend you use RTT. If WVO temps fall at highway speeds or other times, you may find a looped system more suitable.
2. The timing of the RTT changeover valve operation. With a 6 port valve, the return line may carry around 10 floz of WVO to your starting tank (based on W123 IP). This may cause starting issues if this WVO solidifies. If you are able to use a separate valve for the RTT and delay its operation, you may be able to avoid this cross contamination.
3. The suitability of your WVO lift pump. If your pump struggles to pump the amount of fuel required for the RTT to operate correctly, you may decide to use a looped return to minimise the load on the WVO lift pump. NB, this may also be affected by the WVO tank temperature and relative position of the lift pump ie. WVO temp at the lift pump.