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Thread: Oil Pressure Fluctuation Phenomenon

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    XLR8TOR Feedback Score 0
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    Oil Pressure Fluctuation Phenomenon

    Anyone else experience this phenomenon?

    OK. Just got back from a 1200 mile drive from Las Vegas, NV, to Farmington, NM, Gallop, Flagstaff, AZ, Kingman and back to Vegas. Averaged about 24 mpg with my Fiancee and in her ’93 TT. 184,000 miles and it ran flawlessly all the way.

    Just one concern though.

    It seems that every now and then the oil pressure gauge, which usually points to 2:30 98% of the time just below the little icon, would slowly began to drop until it would point to about 4:00 position. I would back off cruising speed of 65 to 75 and it would slowly move back up to its normal position and stay there for sometimes an hour at a time before exhibiting this behavior again.

    Oil full up with 15w-50 Mobil One plus some “No Smoke” that was added to pass the last smog inspection.

    It seemed to do it more often while going on uphill grades but not always. It may also exhibit this behavior only once in an hour of driving and sometimes within ten minutes of the last episode. Slowing down for about 15 seconds would always bring it back up. Engine RPM’s were typically between 2,400 and 2,700 in fifth gear.

    Acts like there might be some blockage of return oil to the pan but the oil is always unbelievably clean for an engine with this mileage.

    It also occurred to me that it might have something to do with the oil temp sensing device that causes the oil to be bypassed through the oil cooler if it get hotter than it should be. If the oil cooler has some restriction in it then that could be a cause of the drop in “indicated” pressure whenever bypass is active.

    Only other thought is a possible loose connection of the wire on the sending unit itself, but that should not be affected by any rpm variance like slowing down a little to cause the pressure to rise again.

    Even though the average temperature along the way was anywhere from 32 degrees to 60 outside so the air was really cool all along the way. Engine coolant temp never varies and has “Water Wetter” in it.

    Any takers on this one?

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    rawr. verified Feedback Score 4 (100%) Atrosity's Avatar
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    The only thing I can tell you is that if you are reading this from the stock gauge it is not the most accurate gauge out there.
    vroom vroom i drive a 93 toyota mr2.

    https://car.social

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    Mine has done this several times since my rebuild. It started at about 6k miles, usually when it was on first start up. I had 20W-50 Valvoline in it during the summer and switched to 10W-40 thinking my oil was too thick. It didn't help. It did it the other day on the highway, I pulled over, shut the car off and checked the oil. (I knew it was ok, but checked it anyway). When I started back onto the road the pressure went back up where it was supposed to be and didn't reoccur the rest of the trip (100mi). I'm subscribed for any help also.

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    Quote Originally Posted by Atrosity View Post
    The only thing I can tell you is that if you are reading this from the stock gauge it is not the most accurate gauge out there.
    That's what one of the guys in the club suggested. But, it doesn't do it ALL the time. So, can a sending unit start acting up when it's about to go out?

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    Yea, fully aware that the stock Gauge is not the most accurate of items.

    Just so we’re all on the same page here I think we are talking about the large round [2” diameter] sending unit facing the fire wall on the drivers side. This sending unit has a slip on connector that can swivel 360 degrees and stay in contact. This connector is my first point of contension to check this morning. Never did seem like a very snug connector from the get go. Would prefer a flat slide on type.

    Maybe a direct reading gauge “is” the only way to go or maybe add one on so they can be compared to each other when this happens. That would definitely tell who the culprit is here when this occurs.

    Possibly of note here.

    My '92 TT, [currently in rebuild stage] in the 18 years I've owned the car, never ever did this to me.

    I also had this same thing happen [same car] when returning from San Diego in July with the desert at 115+. Same thing, just slow down for a few seconds and everything returns to normal even with the heat of the Mojave desert. This would tend to possibly eliminate outside air temperature [OAT] as a culprit. Even then the engine coolant temperature never varied.

    Weird.

    Wonder if pulling the oil sending unit and cleaning it out inside with brake cleaner and re-installing it might help. Since others seems to have encountered this same phenomenon there must be some underlying reason that might solve the mystery for everyone. I hope we can find it then everyone benefits. That's the main reason for forums like this one.

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