Where is my Oil Leak? - NCRS Discussion Boards

Where is my Oil Leak?

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  • Patrick H.
    Beyond Control Poster
    • December 1, 1989
    • 11608

    Where is my Oil Leak?

    All,

    As many of you know I have a 71 350/270 L-48 4 speed. Ever since it was rebuilt 3 years ago I have been chasing oil leak(s). To date, I have fixed the small ones from the distributor, the oil pressure line, and (finally) the valve covers. I still have one that puzzles me, however (at least a little).

    My engine continues to have oil on the REAR surface of the oil pan, and on the FRONT surface of the clutch inspection cover. There is NO oil within the clutch or on the inner surface of the inspection cover. It is dry as a bone there. The oil then goes back across the bellhousing, onto the trans, etc thanks to airflow as I drive along.

    My question is this: is it the rear of the oil pan gasket that leaks, is it the rear bearing seal that leaks, or might I have a totally different gremlin? I know that to fix either requires removal of the oil pan, but I would like to know what I'm in for before I start. And yes, I actually watched my engine as it was assembled, and I know the rear seal is not in backwards. :)

    Thanks for any assistance you can give.

    Patrick
    Vice-Chairman (West), Michigan Chapter NCRS
    71 "deer modified" coupe
    72 5-Star Bowtie / Duntov coupe. https://www.flickr.com/photos/124695...57649252735124
    2008 coupe
    Available stickers: Engine suffix code, exhaust tips & mufflers, shocks, AIR diverter valve broadcast code.
  • Trebor M #25911

    #2
    Re: Where is my Oil Leak?

    Patrick

    There could be a couple of suspect areas of weepage.

    1) The 3 allen head plugs around the rear cam stop are loose.

    2) rear seal is torn.

    3)pan gasket leak.

    4) accessive crankcase presure.

    To have the leak directly in center of rear pan and leak enough to coat under carriage severly I would say it is one of the 4 I mentioned. Dropping the pan on a corvette is not a hard job. The only interference is the center link. Make sure that all leaks from above have been eliminated. Good luck

    Comment

    • Trebor M #25911

      #3
      Re: Where is my Oil Leak?

      Patrick

      There could be a couple of suspect areas of weepage.

      1) The 3 allen head plugs around the rear cam stop are loose.

      2) rear seal is torn.

      3)pan gasket leak.

      4) accessive crankcase presure.

      To have the leak directly in center of rear pan and leak enough to coat under carriage severly I would say it is one of the 4 I mentioned. Dropping the pan on a corvette is not a hard job. The only interference is the center link. Make sure that all leaks from above have been eliminated. Good luck

      Comment

      • Jack H.
        Extremely Frequent Poster
        • April 1, 1990
        • 9906

        #4
        Re: Where is my Oil Leak?

        In addition, that's a 'natural' place for oil to 'pool'. Leaks higher on the block will follow gravity down and airflow will migrate them back. Suggest with all the other due diligence you've done, a good thing to do (if you haven't already) is put car on lift, and steam clean the entire engine down to Chevy orange, then watch to see if oil continues to show up there vs. prior leaks 'moving'....

        Comment

        • Jack H.
          Extremely Frequent Poster
          • April 1, 1990
          • 9906

          #5
          Re: Where is my Oil Leak?

          In addition, that's a 'natural' place for oil to 'pool'. Leaks higher on the block will follow gravity down and airflow will migrate them back. Suggest with all the other due diligence you've done, a good thing to do (if you haven't already) is put car on lift, and steam clean the entire engine down to Chevy orange, then watch to see if oil continues to show up there vs. prior leaks 'moving'....

          Comment

          • Chuck G.
            Extremely Frequent Poster
            • May 31, 1982
            • 2029

            #6
            Re: Where is my Oil Leak?

            Hi Patrick; One of the biggest "leak" areas in small block Chevy engines is the rear of the intake manifold....usually at one or both of the small "V's" where the heads meet the block. It could be dripping down from there. Hope this helps. Chuck
            1963 Corvette Conv. 327/360 NCRS Top Flight
            2006 Corvette Conv. Velocity Yellow NCRS Top Flight
            1956 Chevy Sedan. 350/4 Speed Hot Rod

            Comment

            • Chuck G.
              Extremely Frequent Poster
              • May 31, 1982
              • 2029

              #7
              Re: Where is my Oil Leak?

              Hi Patrick; One of the biggest "leak" areas in small block Chevy engines is the rear of the intake manifold....usually at one or both of the small "V's" where the heads meet the block. It could be dripping down from there. Hope this helps. Chuck
              1963 Corvette Conv. 327/360 NCRS Top Flight
              2006 Corvette Conv. Velocity Yellow NCRS Top Flight
              1956 Chevy Sedan. 350/4 Speed Hot Rod

              Comment

              • Patrick H.
                Beyond Control Poster
                • December 1, 1989
                • 11608

                #8
                Re: Where is my Oil Leak?

                Jack,

                Steam clean a Corvette motor??? Haven't you ever read "How to Detail a Corvette" by Antonick? He considers this a huge no-no due to the loss of original marks with this method. :)

                Anyway, it was, as noted, rebuilt 3 years ago and I make pains to keep it clean. That's half the reason I want to delete the leak.

                Patrick
                Vice-Chairman (West), Michigan Chapter NCRS
                71 "deer modified" coupe
                72 5-Star Bowtie / Duntov coupe. https://www.flickr.com/photos/124695...57649252735124
                2008 coupe
                Available stickers: Engine suffix code, exhaust tips & mufflers, shocks, AIR diverter valve broadcast code.

                Comment

                • Patrick H.
                  Beyond Control Poster
                  • December 1, 1989
                  • 11608

                  #9
                  Re: Where is my Oil Leak?

                  Jack,

                  Steam clean a Corvette motor??? Haven't you ever read "How to Detail a Corvette" by Antonick? He considers this a huge no-no due to the loss of original marks with this method. :)

                  Anyway, it was, as noted, rebuilt 3 years ago and I make pains to keep it clean. That's half the reason I want to delete the leak.

                  Patrick
                  Vice-Chairman (West), Michigan Chapter NCRS
                  71 "deer modified" coupe
                  72 5-Star Bowtie / Duntov coupe. https://www.flickr.com/photos/124695...57649252735124
                  2008 coupe
                  Available stickers: Engine suffix code, exhaust tips & mufflers, shocks, AIR diverter valve broadcast code.

                  Comment

                  • corvgreg

                    #10
                    Re: Where is my Oil Leak?

                    Check the front of your engine next to the fuel pump. There are two threaded holes, and the top one usually goes all the wall through to the fuel pump cavity. This allows you to put a bolt in to secure the pushrod while you're installing the fuel pump. Oil will weep out of this hole and be sprayed back onto your pan and clutch inspection cover.

                    Comment

                    • corvgreg

                      #11
                      Re: Where is my Oil Leak?

                      Check the front of your engine next to the fuel pump. There are two threaded holes, and the top one usually goes all the wall through to the fuel pump cavity. This allows you to put a bolt in to secure the pushrod while you're installing the fuel pump. Oil will weep out of this hole and be sprayed back onto your pan and clutch inspection cover.

                      Comment

                      • Rich Mullikin

                        #12
                        Re: Where is my Oil Leak?

                        Pat,

                        Although most of the responses are potentially valid places for you to start looking, Chuck has given you an area that is over looked by many. My '69 big block gave me similar problems for a long time. It drove me crazy! I tried replacing distributor gasket, valve cover gaskets, oil pan gasket without any success. My problem was a leaking intake manifold gasket. It was located on the left side (rear) where the intake, head and block meet. It was a very small leak but after a few hundred miles, what a mess. I could never keep the bell housing clean. This past winter I pulled the motor to detail the engine compartment and while I had the engine out I fixed the leak. I had talked to a few mechanics who recommended that when I put the new gaskets in to eliminate the rubber or cork end gaskets. Instead put a nice thick bead of silicone down the head, across the block and up the other head. I did this front and rear and the leak is gone. Engine compartment looks better than ever and most important I got to take up that nasty cat litter I had to keep under the car.

                        This might not be your problem, but I would sure check it out.

                        Rich

                        Comment

                        • Rich Mullikin

                          #13
                          Re: Where is my Oil Leak?

                          Pat,

                          Although most of the responses are potentially valid places for you to start looking, Chuck has given you an area that is over looked by many. My '69 big block gave me similar problems for a long time. It drove me crazy! I tried replacing distributor gasket, valve cover gaskets, oil pan gasket without any success. My problem was a leaking intake manifold gasket. It was located on the left side (rear) where the intake, head and block meet. It was a very small leak but after a few hundred miles, what a mess. I could never keep the bell housing clean. This past winter I pulled the motor to detail the engine compartment and while I had the engine out I fixed the leak. I had talked to a few mechanics who recommended that when I put the new gaskets in to eliminate the rubber or cork end gaskets. Instead put a nice thick bead of silicone down the head, across the block and up the other head. I did this front and rear and the leak is gone. Engine compartment looks better than ever and most important I got to take up that nasty cat litter I had to keep under the car.

                          This might not be your problem, but I would sure check it out.

                          Rich

                          Comment

                          • Patrick H.
                            Beyond Control Poster
                            • December 1, 1989
                            • 11608

                            #14
                            Re: Where is my Oil Leak?

                            Already have a bolt in there blocking the hole...

                            Patrick
                            Vice-Chairman (West), Michigan Chapter NCRS
                            71 "deer modified" coupe
                            72 5-Star Bowtie / Duntov coupe. https://www.flickr.com/photos/124695...57649252735124
                            2008 coupe
                            Available stickers: Engine suffix code, exhaust tips & mufflers, shocks, AIR diverter valve broadcast code.

                            Comment

                            • Patrick H.
                              Beyond Control Poster
                              • December 1, 1989
                              • 11608

                              #15
                              Re: Where is my Oil Leak?

                              Already have a bolt in there blocking the hole...

                              Patrick
                              Vice-Chairman (West), Michigan Chapter NCRS
                              71 "deer modified" coupe
                              72 5-Star Bowtie / Duntov coupe. https://www.flickr.com/photos/124695...57649252735124
                              2008 coupe
                              Available stickers: Engine suffix code, exhaust tips & mufflers, shocks, AIR diverter valve broadcast code.

                              Comment

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