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Technical Old flatty low oil pressure when warm?

Discussion in 'Traditional Hot Rods' started by rqzild, Jan 27, 2014.

  1. rqzild
    Joined: Feb 10, 2011
    Posts: 5

    from phx

    I have an early flathead in my rod. 42 I think (crab style distro). When I start the motor cold I have 60-70ibs oil pressure. But as I drive the oil pressure begins to decrease by the time I'm at running temp 175-195 the needle barely registers maybe 5 pounds. At first I thought it was the weight of oil so I went since I do live in az. Running straight 50 right now and same scenario. Any thought?

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  2. Maleficus
    Joined: Mar 25, 2009
    Posts: 33


    Make sure the oil pump is in good nick, if not, replace it, possibly with a higher output one. It should drop as the engine warms but 5 psi at idle is too low, if your oil pump is up to snuff then the engine might be tired and possibly due for a overhaul. The only other thing is a blockage in the oil galleries near the pump, but that is unlikely...
  3. R Pope
    Joined: Jan 23, 2006
    Posts: 3,309

    R Pope

    Most flatties I drove in the '60's had next to no oil pressure, just the nature of the beast. Never took the time to figure if it was just the gauges or if they really had 5#, but they kept on keepin' on, so why worry?
  4. oldolds
    Joined: Oct 18, 2010
    Posts: 3,170


    5# at idle is about right on a used flat motor. New builds have higher pressure because we like to see higher pressure today, but in the old days that was fine.

  5. Is your guage t'd at the filter and try 10-30 or15-40.
  6. 81deeds
    Joined: Dec 23, 2013
    Posts: 66


    I have a 53 flatty...just ran for first time in 18 years....but 18 years ago it was completely not runing external filter...holes plugged at side of block an one on back side of block..oil pressure is 50 cold an zero soon as motor comes off idle presure is 40.....i ran motor at idle yesterday for a hour an ten minutes...motor is absolutely fine.sounds great.. as said above...nature of beast...those motors require minimal pressure.. especially at idle...
    Derek rhode island

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  7. George Miller
    Joined: Dec 26, 2008
    Posts: 413

    George Miller
    from NC usa

    In the old days when they were still running them, that is the way they were.
    I put a high volume pump in mine, that fixed it.
  8. Mike51Merc
    Joined: Dec 5, 2008
    Posts: 3,856


    I read your subject line and my response was "yup".

    Any oil pressure is good oil pressure in an old flatty when warm. Doesn't seem to be a problem for most.
  9. what your witnessing is wear and tear.
    Basically the pump tolerances get looser over years of use so it pumps less volume/pressure when warm.
    aaaaaaaaand the reduced oil pressure is also a sign of bearing wear, as the motor gets older with use, the bearings wear and the film of oil that the rods and such are riding on becomes thicker as more space is available due to wear, so that equals oil that goes through the space faster or with less resistance so you have less pressure build up
    aaaaaaand as oil heats up heats it gets thinner ....basically your problem is due to bearing wear, pump wear and oil viscosity thinning with temperature increase.
    Cheapest thing to do is toss on a fresh oil pump and run thicker oil, like 20/50, an oil that gets thicker with temperature will help.
  10. This sure sounds like the right approach... especially if you're trying to set the idle speed down too low. There's no real load on the engine at idle and it doesn't need a great deal of oil pressure. If the oil pressure picks up when you run it up a bit above idle speed I'd say you've got nothing to worry about.
  11. kjvma131
    Joined: Jan 10, 2014
    Posts: 31

    from New Jersey

    I agree, flatheads don't require much oil pressure. I would get an oil pressure reading with a test gauge right at the block to eliminate a false gauge reading. Always better to test than guess.
  12. rqzild
    Joined: Feb 10, 2011
    Posts: 5

    from phx

    I'll try thicker oil, wouldn't think warm pump would affect flow but maybe. The pressure doesn't really pickup when on the throttle when hot. Cold it does in summer the needle won't even register. So thicker oil and new pump would be the best option?

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  13. J'st Wandering
    Joined: Jan 28, 2004
    Posts: 1,772

    J'st Wandering

    I am trying to understand this. Are you saying that when warm, you have no or very low oil pressure when driving at say 2500 rpm? If that is the case, you have a problem. If it is no oil pressure at idle and when you bump up the rpms the oil pressure comes up, I would say you are ok.

    You are already using a thick oil. What would you go to? Gear lube probably wouldn't be a good choice. :)

  14. Larry W
    Joined: Oct 12, 2009
    Posts: 735

    Larry W
    from kansas

    Not all things are gold with a flatheads .oil pressure is one of them.
  15. Dakota Kid
    Joined: Feb 20, 2007
    Posts: 542

    Dakota Kid

    I had this happen in my flatty. Did you happen put a different cam in this engine? We have found 2 different size cam bearings in the rear journal caused our low oil pressure in our motors if the tolerance isnt correct. The oil pressure gets its reading off the rear journal of the cam.
  16. rqzild
    Joined: Feb 10, 2011
    Posts: 5

    from phx

    Yes when engine is warm regardless of rpm very little pressure. Idle or driving. But 50-70 ponds when cold and it does increase with rpm

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  17. jkeesey
    Joined: Oct 12, 2011
    Posts: 652


    This is just a dumb idea but are you still running the stock fuel pump?
  18. Bader 2
    Joined: Nov 20, 2013
    Posts: 115

    Bader 2

    Still mechanical fuel pump? Or electric? If electric and mech removed there will be loss of pressure because of lack of fuel pump rod.
  19. Bearing Burner
    Joined: Mar 2, 2009
    Posts: 925

    Bearing Burner
    from W. MA

    We had this problem. After we blew the motor found out oil pump screen was plugged.
  20. dsiddons
    Joined: Mar 6, 2006
    Posts: 1,480

    from Indiana

    They don't naturally make good oil pressure. Drive it and enjoy it. It's old enough and tired. Probably got a lot of life left

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  21. Dakota Kid
    Joined: Feb 20, 2007
    Posts: 542

    Dakota Kid

    I tried everything....different gauges, different oil...ect. Around 60-70psi cold and 7 on a cold day going down the highway. Its not that theres no pressure but what oil pressure for the gauge runs off that rear cam bearing area. I believe this is in a VERN TARDEL book.
  22. blowby
    Joined: Dec 27, 2012
    Posts: 7,759

    from Nicasio Ca

    I had my pump out yesterday on my v8-60 due to low pressure. This is a used motor and I had put 10/40 in it previously, then juiced that up with some STP I had sitting around. Gauge was on zero at idle hot and just a blip when cruising. When I pulled the pan (piece of cake on my truck) I found a few things to address. First off all, the bottom of the pan was thick with STP, I have no idea how much actually mixed in the the oil. Second, the strainer had some crap on it, but before cleaning I set it into a bowl of oil and the oil went right through it so I don't think I had much blockage there. Next I pulled the cover off the pump and noticed one edge had been hammered on creating I high spot so the cover was not seating properly. The end float on the gears was also over .010" so I cut that down as tight as I could. Put it back together and some straight 50w. Now I've got 15psi cold at idle and up to 25 but I have yet to take it on the road. V8-60 spec is 30psi at 2,000 rpm. I doubt I will see that but from everything I've read as long as you have anything above idle you're good to go.

    Bizarre how yours could be so high and so low.
  23. neb-rivet
    Joined: Mar 25, 2012
    Posts: 69

    from Nebraska

    Are you running a very low idle speed? Some guys try to run a low a possible and a flatty will idle way lower than a chevy. Try idle at 700-800.
  24. rqzild
    Joined: Feb 10, 2011
    Posts: 5

    from phx

    Pulled the pan and bottom end looks clean. Not sure if its stock pump or aftermarket. But it is mechanical not electric. Hard to believe it could be a bad pump with 70lbs at idle. Is it possible that once the engine runs oil could be getting trapped somewhere there for not enough in the pan to build pressure? Guess I could check oil level when hot. Talked to a guy at a local car show and he mentioned something about a bypass tube but his had the ext. oil filter that he removed I assumed he ment bypassing those connections. This block doesn't have an ext.

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  25. tig master
    Joined: Apr 9, 2009
    Posts: 416

    tig master
    from up north

    Nope The rear cam bearing on a ford flatty is not pressure fed.
    You need to research that before you make that quote about bearing oil pressure taken from rear cam brg.Ask any flat motor guy here and you will find out.:D


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