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Maximum Safe Veg Oil Pressure

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  • Maximum Safe Veg Oil Pressure

    I am admittedly addicted to the pressure gauge sitting next to the rear view. I can't stop obsessing on the pressure readings...

    My pressure usually hangs around 75-80 psi. However, sometimes it runs very high (~99 psi). Not sure if this is a true reading or not, and if so, if it is bad for any part of the system.

    I have not been able to determine and specific condition that causes this. I think it after a fresh fill and when hot. I am assuming it is the fats and PHO that melt and thin out. - no idea.

    Anyway, the question is: doe i worry about the occasionally high pressure readings?
    2005 F350 Harley: Heat Induction Hood, ARE Bed Cover, DashHawk, MBRP turbo back, cat delete, SCT: Tunes by Spartan, Exhaust Sound Videos HERE

  • #2
    I wouldn't...i think its an erroneous reading...if its really hitting 99 psi, all that would be at stake is a fuel line rupture and possibly premature death of the FASS but that I"m not sure of.


    • #3
      Likely you are witnessing the infamous 'fuel pressure spikes'. These are due to the way the split-shot injectors work combined with the addition of 'real' cv's on the fuel lines. You probably see the high numbers right after start-up and after certain throttle/load conditions. Before I went to single-shots in F350, I could almost make it do it on command. Cruising along maintaining speed with very little throttle, when I let off accelerator - it buries the 100psi gauge. The Excursion does this now, gotta upgrade the tranny before the BIG injectors go in it..

      From what I can tell (and after checking a few PSD's plumbed this way), the spikes are only about 125psi - UNLESS there is an injector issue. I met one guy who witnessed well over 500psi. I truly believe he had an injector dumping some injector-pressure fuel back into the fual rail. The spikes are largely why I used the teflon-lined, SS braided hose under the hood on both my trucks and why the Excursion has 100% of the remaining fuel line done w/alum tubing. Its permanent (no 'weathering' from heat and external oil exposure) and all rated for way over 1000psi. Overkill for sure, but thats how I roll.

      I have asked questions on the PSD forums over the years trying to determine what danger to the factory parts is from the spikes AND leaving the pressure in fuel system after shut-down (factory cv's allowed this to bleed off in short order). The consensus was the injectors, fuel rails, etc can withstand ALOT more pressure than that without leaking or causing damage. So, it is really just your rubber fual hoses that are the weak link. I would make it a point to look a them all closely externally everytime I was under the hood and maybe even look inside if I had one off for some reason.

      This is what some of the Weatherhead 250psi diesel fuel line looked like after just several months in VO service under the hood! No failures, but sure freaked me out. One of these lines fail and ya need a tow truck... (btw, the exterior of these hoses looked fine)

      This is my 'permanent' solution - not cheap, but will easily last FOREVER. PTFE-lined SS braided hose with JIC swivel ends:
      2001 F350 XLT 4x4, dually flatbed. 6637 air filter, single-shot injectors, straight-piped, BTS tunes, 200 gal main VO tank - 180k greasy miles
      2000 Excursion Limited 4x4. V3, AIS intake, BTS trans & tunes - 120k VO miles authorized installer

      RIP X & Toyhauler - you served us well.


      • #4
        Fastcote, you are not alone. Mine does the exact same thing. Is it just a matter of time before they rupture? Has anyone had them rupture?


        • #5
          Fuel pressure spikes are somewhat normal for the 7.3. The more wore the injectors are, the higher the fuel rail spikes, an occasional 150psi spike is nothing new. Have to admit though I have never seen 500psi before. FWIW, our hose is 100% bio compatible, and will not crack and weather like the hose pictured by Jason. The working pressure rating is 100psi, but has a 400 psi burst pressure. I have seen a LOT of things happen, but never a burst hose.

          Btw Fastcote, if your normal operating pressure is 75-80, you may turn that down a notch, should be 65-70
          1999 F-350 Lariat 7.3 385,000 miles and counting
          2000 VW Jetta 2.0
          1966 Jeep J-300 with EFI 351W