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  • Too much oil?

    I have heard the story that over-filling the pan on an A engine will cause the rear main to leak. I have no reason to NOT believe this, but I would sure like to understand WHY it is so.

    Anybody with the answer?



  • #2
    First off, the engine has a 3º tilt angle to the rear.

    Secondly, if you have ever had a pan off you would know that there is no real seal between the pan and the rear cap, it is a ½x¼ cork gasket against the edge of the pan, which is about 18ga. If the pan was installed with a dry cork there is nothing besides pressure to seal it. Now, if it was installed with a water soaked cork, the pan will bite into the cork and it will conform to the edge of the pan better.

    My 2¢
    You wana look waaay far up da road and plan yer route because the brakes are far more of a suggestion than a command!


    • #3
      With too much oil, (just my thought) the rear main drain tube (bottom opening) may be submerged in the oil and backlogging oil in the rear main. Thus more oil would find the path of least resistance.
      Sound fair? Jeff
      Twiss Collector Car Parts


      • Mitch
        Mitch commented
        Editing a comment
        The rear main drain tube end is supposed to be submerged in oil. If it is not the crankcase pressures wont let it drain and will cause oil to leak out the rear main. Basically the same as if the tube was missing or broken off

        How's that sound?

      • JDupuis
        JDupuis commented
        Editing a comment
        Ok, I can wrap my mind around that theory.

      • BillLee/Chandler, TX
        BillLee/Chandler, TX commented
        Editing a comment
        Mitch, that sounds plausible except on my car I have a much bigger "pipe" for venting: the fill pipe. Seems to me that the crankcase pressure would use that route.

    • #4
      Ive often wondered if that tube would act like a siphon when the oil level dropped as the engine ran.


      • George Miller
        George Miller commented
        Editing a comment
        I think it does work as a siphon. The oil pump is moving a lot of oil, the return oil is rushing to fill the void.

    • #5
      Originally posted by BillLee/Chandler, TX View Post
      I have heard the story that over-filling the pan on an A engine will cause the rear main to leak. I have no reason to NOT believe this, but I would sure like to understand WHY it is so.

      Anybody with the answer?


      There is no rear main seal so an abnormally high oil level can find it's way out the back. Higher than normal blowby pressures, or crank slop will increase those chances. If the front of the vehicle is on an extreme slope the oil can pour out.

      MY 1 cent
      3 ~ Tudor's
      Henry Ford said
      "It's all nuts and bolts"

      Mitch's Auto Service ctr


      • Mike V. Florida
        Mike V. Florida commented
        Editing a comment
        [QUOTE=extreme slope the oil can pour out.[/QUOTE] just going up hills can be "extreme" enough if the oil is too high.

    • #6
      Many owners over fill when changing oil! About half a qt. does not drain on a normal oil change. I add only 4 1/2 qts when changing oil, check the dip stick after adding that amount.


      • A29tudor
        A29tudor commented
        Editing a comment
        Many dip sticks are not correct, especially after market. A correct dip stick measures 6 5/8 inches from stop on handle loop to bottom of F on stick.

      • BillLee/Chandler, TX
        BillLee/Chandler, TX commented
        Editing a comment
        A29tudor, if the dipstick is correct according to the dimension you gave, is the "Full" level at that point, i.e. the bottom of the F on the stick? If not, where is "Full"?

      • A29tudor
        A29tudor commented
        Editing a comment
        Full is at bottom of F. Mine runs well after adjusting to dimension. No more oil drips or oil needed on 4600 mile trip.

        I use an oil filter, and 5 qts with oil change and it comes to the F mark after with the measurement I indicated.. I don't think that above the F or under the F makes that much difference. Look at the range to the L. Wonder how low you are before you "need to add oil" that is? Maybe a Qt or more? I found that measurements on a Ford Document showing dip sticks for the Fords from A through the early V8s. Check here on page 50 of the Ford Service Bulletins for Aug, 1932, way down in this set of service Bulletins.
        Last edited by A29tudor; 02-21-2019, 11:08 PM. Reason: Ford

      • CarlR82A
        CarlR82A commented
        Editing a comment
        Using original dip sticks with correct F mark and 4 1/2 gt. oil change level over full mark, car level on floor during oil change. Three different cars over 40 plus years.

      • BillLee/Chandler, TX
        BillLee/Chandler, TX commented
        Editing a comment
        Thanks, A29tudor.

    • #7
      Most any engine will tend to migrate oil past the rear seal if the level is high enough. And it seams that once a path is made it will continue to leak until the rear seal is replaced.
      28 Tudor
      57 Tbird
      2kMR2 Spyder
      62 Willys Pickup

      Wise man once told me you don’t know what you don’t know


      • #8


        • Tony Hillyard
          Tony Hillyard commented
          Editing a comment
          That's a really useful diagram, thanks

      • #9
        you could easily calibrate whatever stick you have now. At next oil change, add one quart at a time and make a note of where each quart brings you to on the stick.

        Use a 3 corner file and mark off whatever qt readings you desire

        Also a good way to determine if the F mark on your particular stick is indeed accurate

        Hard to believe they went thru so many designs just for an oil stick


        • #10
          Too much oil? Anybody with the answer?

          Just one simple Model A suggestion.

          A. After rebuilding my 1930 Model A engine, I first inserted a newly purchased and un-marked new Model A dip stick with an "F" mark, but with no manufacturer's marked metal dip stick cross-cut-line.

          B. I next filled my immaculately cleaned and "dry" crankcase with exactly (5) quarts of oil as recommended by Ford, started the engine, and ran the engine until acquiring normal temperature.

          C. Following morning, after engine had connecting rod dipper pans full of cool oil and all cooled oil had drained downwards, I inserted the dip stick, wiped it off, and at the "exact" indicated oil level, provided a crosscut mark ................. and immediately afterwards verified this "exact" level and mark.

          D. After first oil change and after draining all oil, I added exactly four (4) quarts of fresh oil as recommended by the the senior experienced vintage mechanics I grew up with, and ran my engine.

          E. Next morning oil level was exactly on my exact inscribed cross-cut "Full" mark.

          F. Few days later added an oil filter kit and a "vertical" mounted oil filter, (as opposed to horizontal oil filter), on my new modified Model A valve cover.

          G. Later, after first oil change, and draining all crankcase oil, and also emptying the former "vertical" mounted oil filter, I first filled the new "vertical" mounted oil filter to the top with oil, installed it, and added the same vintage mechanics' recommended four (4) quarts of oil.

          H. Following morning, with added new "vertical" oil filter still full of fresh oil, the oil level was exactly on the originally inscribed "F" full mark on my dip stick.

          I. It really does not matter if one has a huge "vertical" oil filter or a very tiny "vertical" oil filter because after it is filled with fresh oil, and after an oil change, the remaining Model A crank case after the first and/or subsequent oil changes only requires four (4) quarts of fresh oil.

          J. If one is traveling in a Model A and checks oil along the highway at a service station, the oil level on the dip stick will never register "F" full. I remember many of the less than honest greedy service station attendants years ago away from home were trained and famous for showing drivers a dip stick with a quart low and next over filling crankcases with a quart of too much oil ...... my vintage mechanic Dad never allowed them to add oil.

          K. From years of past military experiences, there is a very important reason why all of our NATO Military and U.S. Military always prescribes checking all military vehicle engine oil levels prior to start up. Inspector Generals, (IG's) do not tolerate over and/or under filled military combat vehicle crankcases in our U.S. Military during their mechanical inspections.

          Hope this can help to maintain proper Model A oil levels ............. not to mention oil leaks from an over-filled Model A crankcase and multiple avoidable busted butts on a Model A oil slick garage floors.
          Last edited by H. L. Chauvin; 03-12-2019, 12:58 AM.


          • #11
            H. L. I'd be curious to know what your stick measured compared to the 6 5/8" as above.


            • #12
              Hi Jim,

              1. To respond to your Reply #11 Question; and also to try to continue to explain how to correctly mark "any" Model A dip stick for maintaining exactly (5) quarts of recommended Model A oil levels:

              A. First, I bought my dip stick, "new" from Bratton's on June 16, 1998, (21) years ago for $2.00 with Bratton's former Ford Order No. 06750. (Later he changed this order no. to his own order no.of 9890.)

              B. This particular more modern dipstick from Bratton's looks similar to the one in the above illustrated December 1934, page 247 Ford Service Bulletin marked: B6750A and marked Obsolete; however, Bratton's round upper handle is somewhat different in that it does not have the exact compressed, 90 degree circular return to the adjacent straight part of the dip stick.

              C. The original 1934 (6-5/8") dimension on an original dip stick really means absolutely nothing "if" the more modern Bratton's dip stick, or any other parts supplier's more modern dip stick is not manufactured exactly like that of the 1934 model. (For example, depending on the shape of any more modern double steel metal handle at block entry, one dip stick may penetrate deeper into a Model A crankcase than the 1934 model; and one may not penetrate nearly as deeply.)

              D. FWIW: Here is what I did to try to find this "exact" oil depth, which can be measurement using "any" more modern different shaped dip stick, and/or any other different era dipstick. I measured from the top of the cast iron block dip stick orifice located in the Model A block to the exact oil level below.

              E. For example, I inserted Bratton's more modern dip stick into my cast iron engine block, and while the dipstick was inserted all the way down, I marked this more modern dip stick with a fine point pencil at the exact entry point where the handle of the dipstick contacted cast iron block.

              F. From this pencil mark on Bratton's more modern dipstick, to my former (5) quart exact engraved dip stick mark provided about (12) years ago, (i.e., oil level), this distance measured exactly (6-3/4").

              G. FWIW: The measurement from my former dip stick engraved mark to the end of the Bratton's more modern dip stick lower rounded end tip was exactly 1-3/16"; and maybe not too important; however, the overall length of this 21 year old more modern Bratton's dip stick is exactly (10-1/8") long, total, from end to end.

              2. Bottom line, to obtain correct and exact Model A (5) quart oil levels, just buy any new modern Model A dipstick from any Model A parts supplier, and/or use any old Model A dipstick from any era and:

              A. First, insert this dipstick into a Model A engine block, get a sharp pointed pencil and mark the dip stick where the top of the straight part of the dipstick enters the block.

              B. From this pencil mark, measure downwards (6-3/4") along the dip stick and engrave a cross-cut line to mark "Full".

              C. The oil level will hit this mark when (5) quarts of fresh oil is added to a completely "dry" crankcase; and the oil level will hit this mark after draining oil from a wet crankcase and after adding (4) quarts of fresh oil.

              D. Also, if one has a vertical mounted Model A oil filter, during oil changes, empty and discard the used filter and install a new clean oil filter after filling it with fresh oil.

              E. Always check oil level on a Model A engine that rested for about (8) hours, and immediately prior to starting or rotating the engine with the starter.

              3. Thanks to Jim for always posting very helpful Ford Charts.


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