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  • Oil pressure problem

    Hello all I am new so please excuse the newness. I have an 86 cj7 258 six cylinder engine runs great and makes no noise, but the oil pressure is crazy. When you first crank it the pressure reads around 22 lbs. at idle you push the accelerator and pressure drops to 20 lbs. drive it for awhile the oil gets hot and the pressure drops to maybe 6 or 8 lbs. engine still making no noise. replaced gauge still doing same thing old gauge and new gauge are manual. I had oil pan off for new gasket screen was clean on pick up. just bought the jeep so not sure about miles but the guy told me he put a lnog block in it about a 100000 miles ago. If I unhook the line from the block to the gauge and turn engine over oil squirts out to hood. any help would be greatly appreciated. this is my first jeep and am looking forward to making it a daily driver.

  • #2
    I have this EXACT same trouble with my 304 right now. Some things I know to check from my previous posts, but I have not got around to checking yet. Pull your oil pressure relief valve and check for trash between the valve and the seat to be sure it's not stuck open. Check for air leaks in the sump pump screen tube where it meets the block. Ensure that you have the little metal button on the sump pump screen. I was reading the FSM on my 304 the other day, and it looks like anything is possible, but that is the easy stuff.

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    • #3
      Gnarly, when was the last time you replaced the timing chain cover? That might be your issue also.

      newbie, it just sounds like the oil pump has never been replaced. That might be a start also.

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      • #4
        To be perfectly honest, I think 6-8 is not bad. Running 10w 30 in mine I was lucky to get it off of 0. I ran 10w40 and that helped it would be around 6-8. Now I run 15w40 now and it is usually around 8-10 when warm.

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        • #5
          so what is normal up to temp pressure on a 258 just curious

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          • #6
            At idle warmed up mine is around 30-35. Under throttle it's up to 60. I have read that pressure should be at lest 10 pounds for every 1000rpm. In the AMC V8's the timing cover sure can be a problem. I would look at bulltear.com They have a nickel plated one that is supposed to have a lot longer life. They also have better oil pump gears as well.

            High5

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            • #7
              Originally posted by newbie View Post
              so what is normal up to temp pressure on a 258 just curious
              Normal should be about 25 at idle, but how many CJ's with a 258 has 25psi at idle. I had a guy that just put a brand new rebuilt Jasper 258 and he kept trying to tell me the gauges were junk because what only getting 10psi at idle. So he returned like 3 of them before he finally believed me that 258 motors are all over the map with oil pressure.

              One of the kids I coached in baseball had a 258 same year about the same mileage and he would get 15psi, and I would get 4-5.

              High 5 is right though, about 7-10psi for every 1000 rpm.

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              • #8
                Mine was all over the place also, I replaced the pump with a high volume one,same thing. My engine is getting a complete rebuild right now, hopefully it will be more consistant, but if not, I'll chalk it up to being a 258!

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                • #9
                  My father used to tell me if your pressure drops when you hit the gas you have bearing failure.
                  Now I don't know if this is true or not, but it did seem to blow up after that with bearing showing low oil.

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                  • #10
                    Originally posted by Penguin View Post
                    My father used to tell me if your pressure drops when you hit the gas you have bearing failure.
                    Now I don't know if this is true or not, but it did seem to blow up after that with bearing showing low oil.
                    Huh...My father used to tell me drive it till it doesn't go anymore and then take it to a mechanic. I wonder how many times he paid for shop time to fill the gas tank?

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                    • #11
                      funny..... my father used to tell me " get that piece of crap outta my garage" ........ sorry i don't have better input for your pressure problem

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                      • #12
                        Considering the pressure I normally run, I'm wondering if 25-45 psi might be the oil pressure problem. 0-20 psi seems like the norm.

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                        • #13
                          I would think oil pressure at idle should be around 20 lbs,,,

                          Many things can affect oil pressure. Bearing clearances and pump wear I think the most expensive, because if these are the reasons then the engine has jus about seen its better days.

                          If you're thinking engine relatively good,, start checking oil pressure with mechanical guage at block,, if pressure remains low consider dropping the oil pan,, checkng pick up spout & screen,, problems with either of these will affect the pumps ability to pick up oil and will be reflected with poor pressure.

                          I might also look at / for blow by before I dropped oil pan,, observe for smoke or oil blowing out of opening like oil fill and dipstick areas when engine is running,, blow by often be cause by poor piston rings ,, If I observed blowby I would suspect that engine may be a bit worn.

                          I am jus a shade tree wrench and not at all famliar with the 258,, I am sure there are some pretty good wrenchers on this forum,, but I suspect my thoughts arent far from plumb

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                          • #14
                            I'd say you're right on Kelse. Two other things that come to mind, the pump itself, the base cover will wear over time, the pump gears ride on this, once worn the oil will 'bypass' through the worn area, especially at operating temp.

                            There are kits for this, that have a new plate and gears.

                            I would advise against a high volume oil pump. It will fill the top end up, and can starve the pump/lower end for oil. I'm rebuilding my engine right now, partly becuase of this.

                            Blow-by: It can also be cuased by worn valve guides and/or stem seals.
                            It's been my experience that the 258 engine, with some miles on it, wil have some blow-by.

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