I believe that part of my problem with fuel pressure is that I am using OE fuel line for the WVO. If I run a 3/8" or 1/2" fuel line I feel that I will have much more pressure without even heating the oil.
I have made HIH using a rigid nylon tubing inside 5/8" coolant hose, using brass compression fittings.
HINT: To allow the fuel line to pass thru the compression fitting which is used to seal the outlet of the HIH, drill out the compression fitting (usually a double ended male fitting) so that the fuel line can pass right thru it, and still allow the compression fitting to seal.

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Tony from West Oz.
Fatmobile 3 84 300D 295kkm Silver grey/Blue int. 2 tank WVO - Recipient of TurboDesel engine.
Josephine '82 300D 390kkm White/Palamino int.
Elizabeth '81 280E, sporting a '79 300D engine.
Lucille '87 W124 300D non-turbo 6 cylinder OM603, Pearl Grey with light grey interior


Various parts cars including 280E, 230C & 300D in various states of disassembly.