The Best SVO Fuel Line Routing Design?

January 16, 2008

Alaska Vegoil System Fuel Diagram

Hah! There’s two big debates in routing your fuel lines for a SVO-WVO-Vegoil system. First, to loop or not to loop. Second, to add a vegoil lift lift pump or not. We loop and in general don’t add a lift pump.

Not looping your veg return to the veg tank mirrors what most factory diesel system do, which is to return the diesel to the diesel tank. The benefit of a full-return system is that is minimizes diesel use, and purges any air you have in the system, avoiding the most common cause of poor performance and stalling (the other issue being a clogged filter).

Looping, however is what we do. Looping allows a gradual change from cold thin diesel to hot, almost as thin vegoil. It avoids the slug of cold vegoil that is inevitably sitting in the valve and the last few inches of unheated lines that are found in full-return system.

The looped system keeps circulating the heat up front, and allows us to backflush the veg filter with diesel. This backflush primes the supply valve and the few inches of unheated lines with diesel, preventing cold-weather clogging, and minimizing shock to the injection pump. There is no slug of cold vegoil, instead the heated diesel mixes with the vegoil/diesel blend in the purged supply lines, which then loops back again and mixes with the fully heated vegoil. The disadvantage of this system is that it uses a little extra diesel to purge the supply lines and uses the diesel left in the injection pump to blend into the loop.

To summarize: Looping is gentler on your injection pump and has better cold-weather properties. But, it doesn’t purge air and it uses a bit more diesel in order to purge and thin the initial slug of vegoil.

Of course, we use a 12v Vegtherm inside the loop, so we can maximize heat gain, and offer a full backflush. The Vegtherm is shut off for diesel driving, so we’re not lowering the lubricity of the diesel by unnecessarily heating it. Note that we use a Flat Plate Heat Exchanger (FPHE) on the veg side. Some folks create a longer loop into the FPHE, but that system won’t allow a full backflush. Only a 12v heater, of which the Vegtherm is the SVO standard, allows in-loop heating and a full backflush.

Okay second debate: to lift pump or not!

Older VWs do not have separate lift pumps. So no. Older Mercedes do have lift pumps, but the stock diesel filter can be rerouted before the lift pump, so the lift pump can pull from either the veg or the diesel tank, through the respective filter, and then into pump and on to the engine. So no. Fords and Dodges can generally be re-routed as well.

Newer high-pressure systems need a highly-regulated fuel pressure. So in general, yes. The pump that works well is a FASS pump. It’s guaranteed for 2 years on vegoil and has a 23 amp motor. This is not your standard pump, it’s not even the standard FASS pump. If you’re going to be converting a high-pressure (Pumpe-Düse or common-rail/CRD) system you will probably need one of these. An exception is the early Ford Powerstroke HEUI injection systems. In these, the stock filter cannot be rerouted, so provides a billet aluminum replacement filter “bypass” plug, and adds additional filters for both the veg and diesel sides. The good news is that you don’t need the extra pump.

I’ve only had one conversion where the owner wanted a cheap lift pump. They were having starting problems, and their mechanic couldn’t deal with the fuel line rerouting. We put on the cheapo $50 Solid-State Facet Pump (note: These have largely been replaced with their posi-flo pump). These should be considered disposable, but work. It should be noted that it ended being their glow plug relay, not fuel related at all.

Rerouting the lift pump allows the pump to work as it should, avoiding any chance of it pumping into a blocked valve (deadheading), and is cheaper since you don’t need an extra pump. Furthermore, the veg is always flushed from the lift pump, as a separate lift pump needs to be heated, along with the rest of the veg fuel system. The benefit of adding an extra pump is that it keeps your stock system stock, making it easier for mechanic to work on, and provides a fully redundant fuel system.

We believe in robust yet economical vegoil systems. In most cases a looped return and rerouting of the stock lift pump provides the best option for Alaskan winters.

Veg On!


8 Responses to “The Best SVO Fuel Line Routing Design?”

  1. […] Which Truck Should I Get for a SVO (WVO, VegOil) Conversion?13 million gallons of Alaskan fish oilThe Best SVO Fuel Line Routing Design?Which Diesel Should I Get for a SVO (WVO, VegOil) Conversion?Tuning up Vegoil (SVO, WVO) […]

  2. There are so many doubtful point converning the usage of vegetable oil as SVO Fuel.

    In the US it is almost impossible due to he law and regulations.

    In Europe there are only few countries eg Germany where Refined vegetable oil have been used as SVO Fuel in the truck fleets with soem modification on the diesel engine with soem conversion kits.

    The problems are the life span of the negine and the warranty of all the automobile companies.

    There is none approved the 100 % SVO fuel .

    This is a big risk of all individual experiment/operation.

    Will the modified version of the normal diesel engines will be seriously commercial viable ???

    Chumroen Bnechavitvilai
    Bioenergy Devlopment Co.,Ltd.

  3. Aloha Vegwerks,
    Would you still hold to the design shown here for dual tank SVO conversions? Really appreciated the blog and had to sign up to put in the like!
    Dr. Sustainability

    • Will Taygan Says:

      Yes, although there IS merit to 3-and 4-valve designs: a return-to-tank on purge is the standard 3 valve design and/or a loop before/through the flate plate heat exchanger for better and more consistent heat without the 12v veg-therm. I like the 2-valve looped veg return to come in as close the the valve as possible so it provides a backflush of diesel into the veg line on purge. It is not as economical to do this, as it uses diesel to backflush, but it provides excellent winterization and also allow a slow change from cold thin diesel to hot and (slightly) thicker vegoil.

  4. Hi,
    I love this diagram, and I think I’m going to follow your advice and loop my fuel. My question is: Do I need two solenoid valves? Can I just loop it all back to the injectors? Or is the loop only good for purging but not driving?

    Thanks, especially for the straight-forward and crystal clear diagram. I couldn’t do this without folks like yourself.

    Mercedes 240D

    • Will Taygan Says:

      The only permanent loop I’ve ever seen is a factory stock loop on a older Toyota Land Cruiser. Of course some newer common rails do kind of the a same things: 2nd gen 7.3 Powerstroke deadheaded rails for example. I think you would run into air bubble issues on an older 240D, so would encourage you to use the valves, as that keeps somewhat with the stock design.

  5. Ryan Says:

    Is there someone from the arctic vegwerks that can help advise me on purchasing all the components for an arctic friendly set up for my Vw pickup?

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