I complained on the Ford Trucks alternative fuels forum that I was getting lots of smoke and black goop from the F-350’s exhaust pipe when running on WVO, and someone recommended I install a 20-plate flat plate heat exchanger (FPHE).
So I bought a 20-plate used FPHE made by DudaDiesel on eBay.
I also bought from DieselSite a 203° F thermostat, a new water pump outlet and upper radiator hose.
I insulated the FPHE using pipe insulation and hooked it up. Also replaced the thermostat and outlet and hose.
The truck is running noticeably better on WVO now, though the smoke does still come and go. It doesn’t seem to heat the WVO up any faster than it used to, strangely.
But I do seem to have a coolant leak from the vicinity of the FPHE. I’m not sure whether a hose or fitting is leaking or if the FPHE itself is leaking.
I also found — in my Ford service manual because I couldn’t find it ANYWHERE on the Internet — a coolant flow diagram for the 7.3L PSD:
Of course, it’s missing several key details, such as the hose coming out of the passenger side head that then goes into a tee and into the heater core, and then back from there into the water pump. But the key is to understand that the hottest coolant comes from the passenger side head, and therefore that’s where you want to hook up the FPHE. You don’t want to hook to the hose that goes to the water pump because that’s relatively cooler coolant — it has already lost heat into the heater core.