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  • Oil pressure

    I have a 237 flathead. I rebuilt the motor over winter. When I first rebuilt it the oil pressure was about 40. Just recently when I start it the oil pressure stays at forty until it warms up. Once it warms up the oil pressure drops when I get off the throttle. But goes up to 40 when I get back on it. Any ideas?

  • #2
    What does it drop to at an idle, 0?
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    • #3
      The first time I noticed it yea I think it would drop to zero if I let it.. today I didn't have it out as long but it dropped to about 20

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      • #4
        When it was idling in the garage when I got home it went to about 20*

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        • #5
          A quick search reveals that is pretty common for flatheads. Many repeat the same story as you:

          http://www.fordbarn.com/forum/showth...8702&showall=1

          Are you running an electric gauge? Some said a switch to mechanical gauge showed a higher reading.

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          • #6
            what weight oil are you running.

            5w20 and 5w30 will get real thin when it's hot outside like this summer,

            with a flathead I would run a 10w40 or even 15w40 in the summer.

            20 lbs at idle is plenty, but i would like to see 50-60 lbs at anything above 3000rpm.

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            • #7
              Originally posted by olddave View Post
              what weight oil are you running.

              5w20 and 5w30 will get real thin when it's hot outside like this summer,

              with a flathead I would run a 10w40 or even 15w40 in the summer.

              20 lbs at idle is plenty, but i would like to see 50-60 lbs at anything above 3000rpm.
              I just checked I am running 15w40 oil in it now

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              • #8
                Back when your old Flathead was made, there was no such thing as Multi Viscosity oil. As a matter of fact there was very little detergent oil at that time as almost all oils were Non Detergent back in the day. Time has moved on from those days of old. You would be very much better served by running a straight weight oil certainly in the summer. Nothing wrong at all with straight 30 weight oil and I run 40 weight in my Flathead during the summer.

                It is a common held idea that oil changes "Thickness" when the temp of the oil changes, that just ain't so by the way the designation of multi viscosity oil is one of the biggest mis understood parts of the car world. Oil does thin as the temp rises but it sure doesn't happen in reverse and get thicker as it gets hotter as a multi viscosity rating of say 10W30 would suggest. As a matter of "FACT" the meaning of that 10W30 has nothing to do with the weight of the oil, the "W" in 10W30 actually refers to Winter and not weight. What makes multi viscosity oils work is an additive package that contains different compounds that stretch and shrink with the temp of the oil, thus making the oil Protect like 10 weight or 30 weight oil. This protection has nothing what so ever to do with your Oil Pressure. There are about a dozen different chemical formulas that go into this process I won't bore you with those details but suffice it to say you would be much better with a straight weight oil.
                Last edited by Hombre; 08-12-2016, 12:26 AM.
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