Getting ready to convert my truck & have done a lot research on parts required & how the system works. I feel I have a pretty good understanding of everything but system looping or not. This is still a bit of a grey area for me. I don't quite understand what a looped system vs a non looped. Also which is better & which would be better for my 6.5TD engine?

I did some searching on this site & came up with alot of posts but none has really cleared it up for me.

Thanks for any help.

I can't specifically speak for a 6.5 engine as i have a Mercedes.

Here are the pros of looping
-Don't have to run an extra line back to the veg tank
-Faster increase in veg oil temp
-Easier to prime veg line initially

Pros of full return
-Easily purges trapped air
-Sticks with the original design of most diesel engines
-Quicker time to be running on 100% veg (not a diesel blend in the line from purging)

Cons of loop
-Hard to get air out

Cons of full return
-Does not reach highest temps as fast


I know others will chime in on my list, but from my observations and experiences that is what I've noted.

I like a looped return. It works for me. Many will try to scare people away from looped returns because of the possibility of air trapping, but if you have no leaks you will have no problems.

You could always add a 3rd valve and have the option of both a looped AND a full return. I thought about this as I actually have an extra valve laying around but I didn't want spend the extra money for a line back to the veg tank.

Ok, so If I have a non looped return the vegi oil goes from the vegi tank throught the vegi oil system through the IP etc... etc... & back to the tank. On a looped return it does not go back to the tank it is rerouted back to the vegi system. By putting a third valve in you run lines back to the vegi tank & also have it set up as a looped system as well. The third valve alows you to switch from looped to non looped. Is this correct?

In a looped system where do you put the loop? Before the pump,filter, IP ??. Or does it matter?

How it the diesel side setup? Is it looped or not? Just curious. By your post I am assuming they are non looped.

Thanks for the info by the way. Greatly appriciated.

I made valves for my single tanker
Basically I have a full length 3/8" return all the way to the back pickup pump.
Then I pu t a tee in behind the pickup pump and another tee with a valve to redirect to the main line for a loop.
So when I run the heat generally speaking I do not ever want to heat the whole tank in Texas, so I will leave it looped 99% of the time.
If I have any problems with air trapped I just open her back up.
I think it will work great... haven't really tested yet though.

Consider using a limited looped return -

http://biodiesel.infopop.cc/eve/forums/a/tpc/f/15960555...461040542#4461040542

This message has been edited. Last edited by: rkpatt,

quote:

Originally posted by simone0414:
Ok, so If I have a non looped return the vegi oil goes from the vegi tank throught the vegi oil system through the IP etc... etc... & back to the tank. On a looped return it does not go back to the tank it is rerouted back to the vegi system. By putting a third valve in you run lines back to the vegi tank & also have it set up as a looped system as well. The third valve alows you to switch from looped to non looped. Is this correct?

In a looped system where do you put the loop? Before the pump,filter, IP ??. Or does it matter?

How it the diesel side setup? Is it looped or not? Just curious. By your post I am assuming they are non looped.

Thanks for the info by the way. Greatly appriciated.

You are welcome.

You are understanding it correctly. A looped return comes of the return line and goes directly back into the veg line. I have mine after the filter and before the FPHE which is before the INPUT valve. Some loop it to BEFORE the filter. There are pros and cons to this as well. I think most loop it after.

A full return (non looped) does go all the way back to the veg tank.

If you added a 3rd valve you can select either loop or full. As rkpatt mentions there are alternatives to this as well.

The pros and cons of before or after the filter are probably something that coudl be argued for a while. Some will say that if you do it before you keep cleaning your fuel over and over so it will be cleaner. I say that's not true though. Filters are pretty good at getting a majority of the stuff on the first pass, and anything that they miss has already been through the engine's IP, so it couldn't be that big. I think that having a liquid flow through a filter more slowly probably allows the filter to work better. Looping after the filter achieves this. Also keeping the loop smaller means less heat losses and thus higher fuel temps. Though this is probably a moot point.

I think the important thing is to return it before the FPHE. This way the fuel gets heated the second time through. It will have lost some heat on it's first trip through and on the way back to the T.

Don't loop the diesel side. Leave it like it is. Your T is before the selection valve for the input side. so if you leave it on loop for running on diesel, you will actually be pumping all return fluids into the veggie tank, not looping them. Also , there is no need to, and there are reasons why looping diesel can be bad.