When you switch the valve you switch the source and return of the fuel going to the engine at the same time. All of the trapped fuel contents of the filter and lines to the engine doesn't disappear when you switch the valve. The valve simply changes the source of the fuel and where everything between its inlet and outlet (that isn't used by the engine at that time) and returns everything in the lines and filter back to the new source. So in other words, everything gets mixed from the outlet of the selector valve, thru the lift pump, the contents of the filter, contents in the injecton pump & return line, back to the selector valve, and then its returned to newly selected tank.

 

Minus what you burned in the engine. I fail to see how this would be useful in mixing your veggie oil. The amount returned would be insignificant.

 

Clay, I think you are missing the point Trebor is trying to make. If you are trying to keep the two fuels seperate, the best course of action is to place the valve as close to the engine as possible, and run seperate lines all the way to the front from the tanks.

I agree that it's an insignficant amount, but if the truck is run mainly on veggie oil, then the fuel in the diesel tank could be there for months. Every time the valve is switched, a little more veggie comes in - with the level in the tank dropping slowly but surely from the warmup and shutdown running. This could mean a dead truck on a cold morning, so it's a point that should be kept in mind by anyone running such a setup.

The obvious cure is to run the diesel tank down from time to time, and dose it liberally with anti-gel additives in cold weather.