I have converted a 1983 Mercedes Benz 300 SD to WVO. The oil tank has overflowed. When I drive on OIL, it looks like oil and diesel are being returned to the oil tank. My diesel fuel gauge decreases and the oil tank seems to increase. Any idea what I have messed up or is wrong?

If you are switching the returns for diesel and oil to each tank respectively, I'd say your return valve is defective. The lift pump pumps a large amount of fuel so there is a lot of excess that is returned to the tank.

You need to describe your plumbing a bit better, and then you will get an accurate response to your question.

I am switching with an electronic switch from x. Something has been bad since I installed the change. One line from the motor then split under the car in the rear going to each tank overflow.

When I turn power on the switch, it flows to the oil tank and stops when I turn the switch off. Why would it use Diesel fuel?

I will try to test the switch this weekend to see if it is working correctly. Thanks.

quote:

Diesel fuel gauge decreases....Why would it use Diesel fuel?

Sounds likemaybe your fuel selector valve is allowing both fuels in. Not sure if thats even possible 'tho.

I have checked the switch and it is working properly. I notice when I shut off the oil and go to deisel while I am still sending the return (flush) to the oil tank that the fuel never clears. It looks like WVO while I am flushing. Is there a way to check the lines? How can I tell which diesel line is the tank and which is the overflow? Could I have the line connected wrong?

I've had the same problem from time to time. The 6 port valve would stick with the Diesel going to the VO tank. It took some looking to figure it out but since I figured out what was happening when the back tank starts dropping, I check the 6 port valve and tap on the valve. Fixes the problem everytime.