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Oil Pressure Issue, Dry Sump System

Discussion in 'Road Side Pub' started by Mainn, Sep 8, 2019.

  1. Mainn

    Mainn Member Established Member

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    Thought I'd pick your brains here, and see whether anyone can come up with something I failed to think of.

    I'm having an oil pressure issue on a freshly built engine (Ford 1600 XFlow). Running a dry sump system.

    I was tracking a car last year when oil pressure dropped off a cliff over the course of a lap. Pulled off and got a tow back into the paddock. Tested the sensor and established that it wasn't that, so we pulled the engine out and sent it off to be rebuilt. Bearings were stuffed. (that was a baaaad weekend)

    The engine was rebuilt and put back in the car. Ran it on the dyno and the exact same issue occurred (luckily, the bearings survived this time so it wasn't AS dramatic). Oil pressure is fine - until you get to about 80C oil temp. When oil is cold, it's perfect - it can idle at 70psi. As the oil temp increases, especially over 80C, oil pressure just suddenly starts to drop off rapidly - 5psi at idle and 25psi under throttle. Waaayyy too low. Running 20W-50 mineral oil as well, which is way thicker than I'd like to run. Swapped the oil pump, same issue. Pulled the engine again and the builder went through it again just in case they missed something, and said it actually looks perfect inside (glad there's no damage from the low oil pressure).

    So, it has to be related to the dry sump system somehow. But what could it be, which only occurs when the oil gets hot??

    I've come across a lot of bizarre car issues, but damn, this one has us pretty confused. If anyone has any knowledge of dry sump systems, and/or has an idea, I'd be more than happy to hear it!!

    PS not sure if this is in the right section - if not, please move mods.
     
  2. lexustech48

    lexustech48 RIP FoMoCo 1903-2014 Premium Member Established Member

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    Good morning (afternoon?)!

    Is it at all possible that you have a crack in your block that goes through the main oil galley? Engine gets up to temp and expands juuuuuussstttt enough that you lose pressure?

    Perhaps an issue with your oil pump scavenging system?
     
  3. derklug

    derklug Seriously? No, never. Established Member

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    Saw a bad braze joint on the pick-up tube once that would suck air, but that was on cold oil.
     
  4. Mainn

    Mainn Member Established Member

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    Good afternoon! It's 2am here. Really not sure what I'm doing up, hahaha. Stupid race cars, having me think.

    Interssting idea you have there. I wouldn't have thought that the relatively low temp would expand it enough though to cause such a dramatic loss in pressure. That's a tough one as it would be impossible to pick up on the test stand. As it would be such a big issue if it were the case, I will have to try and eliminate everything else first, before this could reaaally be looked into more. EDIT: oh boy, despite mentioning it in the next paragraph, I completely forgot the oil would also get thinner at hotter temps and leak through cracks more easily too. D'oh. Still, would prefer to eliminate everything else first before jumping to the worst of stuffed block.

    The ONLY idea I have at the moment, is that the oil on the inlet/scavaging side is being aerated somehow, but only enough to become an issue when the oil gets hotter and thinner. How/where? Not sure, don't know enough about dry sumps - other than a low oil level potentially causing that? I considered whether the liner inside the oil lines on the suction side are collapsing (sorta relates to your scavenging system point), but figured that would happen at cold temps too. Could be wrong here though, more than happy to be corrected and learn.

    I really don't know enough about dry sump systems to have a strong idea, so I'm all ears.
     
    Last edited: Sep 8, 2019
  5. Mainn

    Mainn Member Established Member

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    I'm sure I'm going to read that post in the morning when I'm a bit more awake and go "what the heck was I trying to say?" but for now, you get the idea!
     
  6. Coiled03

    Coiled03 Well-Known Member Premium Member Established Member

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    If it's temp related, you could definitely pick it up on the stand, as long as you run it to high enough temp and monitor oil pressure. Did you magnaflux the block? Might be worth it if you haven't.

    That aside, I'd suspect oil pump internal clearances. When viscosity drops with temperature, it can cause a pressure drop with it. I know you said you swapped pumps. But if you put in another one of the same brand, and the same clearances, the problem would remain. Read through this:

    Drysump pressure drop - Engine & fuel engineering - Eng-Tips

    Lots of other things to investigate in there.
     
    lexustech48 likes this.

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