Coolant heating diagram for SVO/WVO/UCO/UVO fuel systems

I thought I would make a coolant heating diagram that shows how to tap into the coolant system of a Mercedes 300D. The same principle will apply to most vehicles. Just remember that the veg oil heating circuit and the flat plate heat exchanger (FPHE) must be in parallel with the main coolant circuit, and not in series. If you connect it in series then you need to have your cabin heater on at all times to keep the coolant flowing through your FPHE:)

Vegetable oil flows through the FHPE on its way to the filter, and takes up heat. Typically with these FPHEs, the oil is heated to within a degree or two of the coolant's temperature. They are extremely efficient and far better than the copper coil variety which can also cause copper ions to enter the veg oil and contribute to oxidation and polymerisation problems.

If you need to heat your tank as well, you could add a 2nd FPHE in series with the 1st FPHE and use that to reheat the oil in the veg oil return line before sending it back to the tank. Nice and simple, and it doesn't heat the oil too much; just warm enough to keep it nice and liquid to aid the flow and reduce problems associated with the oil's high melting point components clogging the lines and fittings.

While on the subject of heating the veg oil tank, I've seen some designs that extend the main coolant circuit all the way back to the veg oil tank where it heats the oil via a coil, before sending it back to the engine. This is not a particularly good idea for the following reasons:

• increased risk of rupturing the coolant and damaging your engine.
• if the heater coil is metal, particularly copper or aluminium [aluminum to our American friends ;) ], it will contribute to oxidation/polymerisation problems in the tank, because these metals are very good pro-oxidants.
• It could heat the oil too much, and again contribute to oxidation/polymerisation problems.

For a larger pdf version, please click this link