Twin fuel feed

Single Tank WVO systems and blending SVO WVO to thin it.

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Twin fuel feed

Postby Bones » Sat Sep 19, 2009 10:44 am

Here's an idea that I have been toying with for a while.

I currently run a '98 300TD MB on roughly 95% svo without problems, I would go to 100% as its summer here if it wasn't GM modified soya which is very 'sticky'.

Quite a few on the MB UK forum also run the same MB's without mods but do have fuel starvation issues during the winter which leads me onto my idea

The fuel starvation is caused by the 6mm ID metal feed pipes but also the high throughput of the fuel system returning large quantities back to the tank.

One way to overcome this would be to loop the return with a three way valve then un-loop once the engine is hot, I wanted to add to this by also switching the return pipe from the tank into the feed also giving you an extra 6mm pipe.

It would mean another three way switch but should provide all the flow when cold, again, when hot switch back to normal.

Any thoughts?
:idea: :idea:
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Postby Bones » Sat Sep 19, 2009 2:18 pm

Btw, the background to this idea was from a friend whose 300TD had a blocked fuel strainer while he was out -

cunning as a fox he switched the fuel feed and return around so it pump fuel through instead of pulling it - got him home ok :D
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Re: Twin fuel feed

Postby SunWizard » Sat Sep 19, 2009 9:09 pm

Bones wrote:The fuel starvation is caused by the 6mm ID metal feed pipes but also the high throughput of the fuel system returning large quantities back to the tank.

I think most of the starvation is caused by the filter having a hard time passing the thicker VO, not the pipe ID. Looping the return would help some since you have less going through the filter. If it gets cold enough (<20F for non PHO) you will still clog the filter after a varying amount of miles.

Doubling the pipe would make little difference. Adding heat with a FPHE is the best change you can make.
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Postby David » Sun Sep 20, 2009 10:00 pm

When I got my MB it broke down a few KM from where I bought it.
After finally getting it home ( on a trailer) I found the fuel pickup was coated with what looked like plasticine.

I tried the reversal of the pickup and the feed lines but there was so much water and crap in the tank this also failed to fix the problem.
Some people just remove the screening as it really dosen't do anything a filter upstream won't do a lot better.

I have run oil in the OEM metal lines and had no problem with starvation even when towing a heavy trailer that requires full throttle for long periods of time. Some people have done conversions using 5/8 hose but my experience has shown this to be completely unnecessary in temps I use my vehicle at which are down to 0oC.

At temps below this, I would suggest that some sort of thinner be added to the fuel such as Kero or Dino and a HE before the filters would be mandatory. I also agree that the filter is most likely to pose the largest restriction as the difference between the viscosity of Dino which they were designed for and Veg is huge especially at low temps.
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Postby jburke » Wed Sep 23, 2009 7:03 pm

Add a parallel fuel filter
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