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Thread: school me what oil pressure guage does.....

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    Senior Member bellwilliam's Avatar
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    Default school me what oil pressure guage does.....

    yeap, I am an idiot. but I have no idea what the point of an oil pressure gauge. Every race car build, I would install oil pressure gauge. Never looked at it, till an engine gets a rod knock, then I will take a peek to confirm there is zero oil pressure

    I know what water temp (> 230F, bad), oil temp (don't step on it till >170F), Volt (>12v sitting, >13.3v charging), fuel pressure (pressure = good), A/F (<10 and >15 bad, a little more complicated than that), , gauges does. But oil pressure gauge nobody ever said anything that isn't vague. best I've heard is 10psi for every 1k rpm, BS, my Vette oil pressure at 900rpm is 35psi.

    so tell me EXACTLY what to look for with an oil pressure gauge.
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    Kam
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    From what I understand, so you can see if you have pressure or not. Idiot light would solve that problem.
    But, the key thing is, LOGGING your oil pressure. That way you can see if you're losing pressure in a corner, etc.
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    Not Certified Slow SDSUsnowboards's Avatar
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    I'm just guessing here: Trouble shooting? If you see lower or higher pressure than what you normally see, then it's a hint that something is going wrong. The other gauges won't tell you that.

    Not to derail this thread, I was wondering if there would be any method to wire a relay that shuts power to the fuel pump when the oil pressure sensor senses pressure below a certain psi (voltage?). Could save an engine by immediately forcing the driver to coast to a stop with the engine off.
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    Senior Member bellwilliam's Avatar
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    Quote Originally Posted by SDSUsnowboards View Post
    Not to derail this thread, I was wondering if there would be any method to wire a relay that shuts power to the fuel pump when the oil pressure sensor senses pressure below a certain psi (voltage?). Could save an engine by immediately forcing the driver to coast to a stop with the engine off.
    it would be from an ECU. ECU can go into limp mode with a combination of parameter
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    Shutting off power mid way in a high-g corner (where oil pressure is most likely to fail) could have catastrophic consequences as weight balance suddenly (and unexpectedly) shifts forward!!

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    RaceTape Ninja Force McCocken's Avatar
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    The OPGs I used with Miatas (the real ones from the earlier models) told me a few things, and I monitored them as closely as my water temps. They will twitch backwards during detonation, even events I couldn't discern with my ears. I verified a few of these twitches against datalogs and a knock sensor.

    Variations under certain maneuvers, like a decrease under hard braking, fluctuation in pressure at higher RPMs also gave me warning of low oil in the sump (I solved a lot of that with a static sump baffle plate). The gauge also helped tell me when my oil temps were up to spec by the readings at certain RPMs. Cold, with my shimmed oil pump, the gauge was pegged. When the OPG settled to 50psi at speed, I knew the oil was up to temp.
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    On my Radical watching the oil pressure was essential. Using a 15-50w oil the pressure was quite high until the engine got up to temperatures. Even running the car for 15 minutes before going on track it was often challenging to keep the pressure under 100psi. Apparently running oil pressure over 100psi can cause the oil cooler to burst in these cars. I don’t know if it is an issue with other cars.

    Charley

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    Logging the data is key so you can see trends as well as the sudden dip towards 0 as you dive into a corner under braking. If your eyes are on the gauge rather than the car beside you at that point you likely have other issues or your last name is Senna. Often we catch motors that are starting to take big gulps of oil and can triage them to live for the weekend once we know they are drinking. A miata w/o oil cooler only has ~4qts of oil so it doesn't take too much of a drink to kill the engine. The data can be scary though as some motors have single digit pressure at idle but decent op at rpm.
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    ^^^^ What he said.

    You will never be staring at the guage when an event worth noting happens. It might even take you precious seconds to recognize that your "OMG shut it down" light is on and take action.

    Oil pressure gauges are mostly placebos for guessing at whats going on. Datalogging oil pressure will tell you whats really going on. IF you have a standalone, setting a failsafe on your oil pressure feed is a thousand times better than having a gauge.

    I have the Kpro in my S2000 configured to impose a 2k rpm rev limit and flash CEL if oil pressure falls critically low. Its never done it, so at this point, it working is purely theoretical but i believe the philosophy is sound. Additionally since presumably you keep data, it at least gives you a body of work to reference as the motor ages.


    FWIW i have a page on my SOLO DL configured with Oil pressure/temp water temp and voltage to act as auxiliary gauges in the pit or on the street to scratch the gauge itch should i feel it.
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