I seem to have over purchased slightly on the copper tubing so if you want a heat exchanger for your self then £35 will secure one for you delivered to your location in the UK.
My design is the standard jacket type. A large diameter (28mm) copper pipe is inserted in the hottest part of the engine coolant flow. Wrapped around that pipe is a copper jacket which maximises the surface area which can contact the water pipe.In my design, this is a 35mm jacket with a 28mm internal coolant pipe.
This will give significant oil heating even at relativly high flow rates. My tests show that 50 degrees C is the ideal temperature for SVO to acheive a low viscosity.
My design is soldered together just like your home plumbing system. This minimises bulky compression fittings and heat loss. Fuel system connection is made to the two 6mm Internal Diameter copper pipes which protude slighly from the oil jacket.
If necessary, the whole jacket could be insulated to minimize the chances of losing oild temperature to the surrounding air.
This design minimises the chance of fuel system contamination as the central copper water piper is completly unbroken.
I would suggest that you install the exchanger after the solenoid in a two tank system so it can be as close to the injector pump as possible.
In my car, I have only about 1 meter of pipe and the jacket between the solenoid and the injector pump, so I’m confident that the changeover time is minimal, perhaps as low as 5 minutes at tickover.