How to Make and Install a Hose on Hose HOH Heated Fuel Line for a WVO Conversion

I use 3/8" bendable or soft aluminum tubing, 1/2" heater hose and electrical tape. You can size your lines as needed. I feel that the 1/2" hose flows enough coolant. It's smaller and fits closer to the bottom of the car. I like the aluminum tubing instead of rubber fuel line. The metal tube transfers heat better and the line is smaller. It's also cheaper then rubber fuel line and should last much longer. It will keep the HOH closer the bottom of the car and prevent drooping. It's available online from Aircraft Spruce, McMaster Carr or Graingers. Just be careful not to kink it when you are working with it. If I an converting a truck I will insulate the line with foam pipe insulation. The stuff for air conditioner lines is a little nicer than the stuff for pipes, but they both work. I like to wrap the insulation with duct tape to help protect it from the elements. If I converting a car I skip the insulation so I can have maximum ground clearance.

Estimate the length of fuel line you need and add a few extra feet. You do not want to run short. I let the coolant line run longer than the fuel line. I want it to reach the next connection without the use of a coupler. Lay all three lines on the floor (four if you want to return to the tank). Put the fuel line in-between the coolant for better heat transfer. You could wire tie or zip tie the lines together. I prefer electrical tape. It will take a couple rolls, but it's cheap from Harbor Freight. The tape will provide better heat transfer than wire ties because it holds the lines together tightly.

If I am converting a car I will put the drive tires on ramps. I use my floor jack to lift the other end and secure it with jack-stands. Shake the car to make sure it will not fall. Find a safe route for the HOH. Make sure to stay clear of moving parts and the exhaust. I like to run the lines along the inside of the frame rail when I working on a truck. I follow the factory fuel lines on a Mercedes.

My WVO tank is in the trunk so I need to drill a hole for the HOH. I like to drill a pilot hole from under the car to be sure that I drill the right spot. I used a 2" hole saw and filed the rough edges. I made a grommet from a scrap piece of rubber fuel line. Cut the fuel line length wise and push the slit around the sheet metal.

I begin installing the HOH from under the car. It's easy to feed one end into the truck and the other end into the engine compartment. It's tougher to start at one end of the car and try to feed the HOH all the way to the other side. There is less chance of kinking or chaffing the HOH when you start in the middle. Run the HOH around the rear suspension and into the trunk. Make sure you go around and over whatever parts are in your way. If you miss one you will have to pull out the line and start over. Feed enough into the trunk to reach the tank. Secure the HOH to the bottom of the car with clamps and self drilling screws. Get one or two clamps on the line to hold it in place, then feed the other end into the engine compartment. I like to go up between the oil filter and the brake booster on a Mercedes. Finish clamping the HOH to the car. Watch for anything that can rub or puncture the line. Three to five clamps should be enough if you used aluminum fuel line. You may need more clamps if you used rubber. It's much easier to have help, but you can install the HOH alone.

Connect the HOH to the WVO tank. I plumb in all of the parts and bleed the air out of the coolant lines with a garden hose before I connect the coolant lines to the engine. Don't worry about filling it with straight water. Just start the car and it will mix. A heater pump from a Mercedes could be installed to help circulate the coolant at idle. I use a vacuum hand pump meant to bleed brakes to suck the WVO up to the engine. Make a to use vacuum jar or a few feet of clear hose so you can see the WVO before you suck it into the pump. The car should switch over without missing a beat if you bleed it first.