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Rapidly Fluctuating Oil Pressure Gauge

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  • Rapidly Fluctuating Oil Pressure Gauge

    Hey Folks,

    I've got a 2000 Crown Vic w/150k that has a funky rapidly fluctuating oil pressure gauge. It only happens when coming to a stop after 15+ miles or so on the freeway. It returns to normal when shifted to neutral or park or when you hit the gas.

    Here's a link to a video so you can see what I mean:

    I changed the oil and filter and cleaned the electrical connectors on the oil pressure sending unit to no avail.

    What would you recommend as the next steps to remedy this?

    Thanks in advance for any suggestions!


  • #2
    Re: Rapidly Fluctuating Oil Pressure Gauge

    I agree with badaceds650. Just because you cleaned the connection doesn't mean the part isn't bad.
    You can do anything except light a paper match, on a marshmellow, underwater!

    R.I.P. Taylor and Chris


    • #3
      Re: Rapidly Fluctuating Oil Pressure Gauge

      +1 on the sending unit


      • #4
        Re: Rapidly Fluctuating Oil Pressure Gauge

        Thanks for the replies!

        I replaced the sending unit over the weekend (it was only $13!) but unfortunately, it's still occurring.

        Replacing the sender seem to increase the sensitivity. It will happen after only a mile or 2 of driving and when creeping to a stop. It used to only occur when completely stopped after a good jaunt on the freeway.

        Any advice/ideas/suggestions for the next steps are greatly appreciated!


        • #5
          Re: Rapidly Fluctuating Oil Pressure Gauge

          I have a 2002 CNG CV PI with 75k and it was doing the same thing. I replaced the sender and nothing. It was after I replaced the oil with Royal Purple 10-30 and a K&N filter that cured my problem and gave me an extra 5 more mpg
          My brother has used it for years and has had great results.

          Hope this helps.
          Last edited by 02cvpi; 06-16-2009, 09:53 PM.


          • #6
            Re: Rapidly Fluctuating Oil Pressure Gauge

            Thanks 02CVPI! Yeah, Royal Purple is good stuff, I used it in my Prelude before with good results. I think I saw it at my local Pep Boys lately as well.

            I just changed the oil with Mobil 1 5w-30 and a Motorcraft filter and it didn't seem to make any difference with the gauge fluctuation.

            I was considering hooking up a mechanical gauge to really see what's going on with the oil pressure.

            It's pegged L a few times lately which makes me concerned..


            • #7
              Re: Rapidly Fluctuating Oil Pressure Gauge

              Looks like you need a new oil pump. If things dont improve you could sieze your motor.
              BLUE 09 GX


              • #8
                Re: Rapidly Fluctuating Oil Pressure Gauge

                Yeah, I was afraid of that!

                I want to install a mechanical gauge to really see what's up with the oil pressure. Not sure which one to buy or how to route it back to the passenger's compartment though. just tape it to the windshield?

                According to my factory service manual, it looks like getting to the oil pump requires lifting the entire engine! What a pain!

                If it requires replacing the oil pump, I'm seriously considering installing a low mileage engine. I see them for ~500 on craigslist.. but they are from regular, non-CNG vic. The compression ratio is different, right (10.1 vs 9.1)?

                What else is different? How bad of an idea is this?

                I'm thinking for a few hundred more a low mile engine would be a good thing vs. just replacing the pump.


                • #9
                  Re: Rapidly Fluctuating Oil Pressure Gauge

                  Hmmm, new engine, or trying the 10-30 Royal Purple like I did for about 40 bucks. It worked wonders for my car The gauge is like an idiot light without the actual light. The gauge is not really measuring pressure. It is similiar to an oil pressure on and off switch. There is a fix that allows it to function like a real gauge posted somewhere on the net that shows how to make it a real switch. Here is part of the post I found; The stock oil pressure gauge is little more than an idiot light that uses a pointer. I modified mine to be functional, but depending on the year of your car, that could really be a pain in the butt.

                  If you look at your oil filter adapter where the stock oil pressure sending unit is, you will find a second threaded hole with a plug in it. You can use that to install something like this:
                  Last edited by 02cvpi; 06-17-2009, 11:44 PM. Reason: removed advertising that I didn't put there


                  • #10
                    Re: Rapidly Fluctuating Oil Pressure Gauge

                    Well I finally got the mechanical gauge installed.

                    Here's a video of me coming to a stop. You can hear the stock gauge fluctuating in the background:

                    Here's one where it once was pegged on L!:

                    So, does it look like a oil pressure issue or just a gauge issue?

                    I'm getting ~35 PSI @ 75mph.

                    Thanks in advance,



                    • #11
                      Re: Rapidly Fluctuating Oil Pressure Gauge

                      Well installing the mechanical gauge has really told an interesting tale!

                      Hot idle in D, foot on brake = 5-7 psi - It will only read this low after driving 20+ miles.
                      Hot idle in P or N = 10 psi
                      Cold startup = 70 psi

                      When I first get on the freeway:
                      36 psi @ 55 mph
                      40 psi @ 70 mph

                      after 20 miles:
                      22 psi @ 55 mph
                      27 psi @ 70 mph

                      I drained out the Mobil 1 5w-30 and tried Royal Purple 10w-30 based upon the recommendation here. It picked up a pound or 2 of pressure when moving, but the hot idle didn't change and is still around 5-7 psi.

                      My shop manual says it should be between 20 - 40 psi.

                      I've been told this can be attributed to excessive clearances in the main and rod bearings or a bad oil pump.

                      If it's the bearings, I was told to look for a large psi change when letting off the gas then resuming at cruising speed. I only notice a 2-3 psi change when I do that. I'm honestly doubting bearing wear, as I've heard these CNG engines burn very clean.

                      If it's the oil pump pressure relief valve, wouldn't the pressure skyrocket as RPMs pick up? Although I'm not totally certain how these work. I've heard sticking relief valves will sometimes make the oil filter balloon and leak.

                      Either one of these scenarios seem to require removing the engine. Can someone confirm that? What a bummer!

                      If that's the case, I can't see just see spending all that time and money to remove the engine, then spending $150 in parts or so repairing the oil pump or bearings and putting that 152k mile engine back in when I can find low mile engines for ~500. I'm really thinking of just driving this till it pops, then swapping engines. Or have I boarded the train to crazytown?

                      I really like the idea of installing a low mileage motor, I just don't know what the internal differences are with these CNG motors. I've heard the compression ratios are different. What's that attributed to? Different pistons, heads or crank? Swapping motors on regular Crown Vics doesn't sound incredibly difficult. What snags will I run into if I decide to swap?
                      Last edited by CNGBiker; 05-19-2008, 04:56 PM.


                      • #12
                        Re: Rapidly Fluctuating Oil Pressure Gauge

                        Wow, I am interested in what some of the mechanics have to say about this.

                        It used to be that you could change the presure relief valve from out side the engine. I don't have a clue on this engine if you can. My guess is that it looks like a worn out engine. Does it use oil? How many miles per quart?

                        I guess it could be the pump, but as far as I know they usually last as long as the engine.

                        Like I say, I am not a professional mechanic. And, I would like to hear what some others have to say.


                        • #13
                          Re: Rapidly Fluctuating Oil Pressure Gauge

                          Did you ever find out what was wrong with your engine? Is it the oil pump? I hear you don't have to yank the engine to change the pump. You have to lift it up a bit to remove the oil pan and pull the front covers off too. Might as well change the rod bearings while you are in there.


                          • #14
                            Re: Rapidly Fluctuating Oil Pressure Gauge

                            Nope, I never did find out what was causing the low oil pressure. I put another ~28k miles on it before it blew a head gasket and was replaced with a low mile engine out of a '04 Crown Vic.

                            A member at was going to pick up my old engine, disassemble and inspect the internals to salvage whatever parts he could, but it was picked up by the scrap yard before he could retrieve it. So I guess it will remain a mystery!


                            • #15
                              Re: Rapidly Fluctuating Oil Pressure Gauge

                              The replacement engine was it a CNG or a gasoline engine. Inquiring minds want to know??