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Old 05-14-2008, 11:00 AM   #1
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Default Oil pressure sender difference 91 to 93?

Ever since I've had this new miata I've noticed the oil pressure reads low. At idle I see what looks like 10-15psi, I'm used to seeing 25psi, never see above 60psi when WOT. This is with 10w-30 and a Purolator filter.

I can't remember if it was like this on the original engine and pressure sender as i only drove it like that for about a week and I never payed heed to it.

I'm wondering if my 93 sender has a different resistance scale as the 91? It moves like it should, but the scale is off. I guess if I really cared I'd hook it up to a gauge myself, or try to swap the senders.
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Old 05-14-2008, 11:16 AM   #2
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My 92 reads like your 91 did. I never see below 25 ish psi.
I assume your using the sender that came with the newer car and not the one you originally had on that engine?
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Old 05-14-2008, 11:33 AM   #3
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They used the same sender 90-94
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Old 05-14-2008, 11:40 AM   #4
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This is very common Scott, as Ben says they use the same sensor, but everyone reports different readings, I assume the purpose of the sensor is really just to give you an idea of your actual pressure.
When I went from syn 0-40 to conventional 20-50, my OP went from 10-15 idle (which was scary low based on previous pressure with same oil weight prior to oil consumption) to 15-20 idle and as high as 80psi at high RPM under WOT.
I assume you have checked your compression and performed a leakdown, so you should not worry.
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Old 05-14-2008, 11:47 AM   #5
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yeah I was reading on m.net. Someone dude has 4 miata; all four report different pressures with the same oil and filter.

he hooked a gauge to each, teed off the sender port and the were all within a few % of each other on that gauge.

I'll guess i'll chalk it up to that. I just dont like seeing it that low, but beats me last engine where after about 500 miles if i came to a stop it would drop to 0 for a few seconds since it would burn so much oil
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Old 05-14-2008, 01:22 PM   #6
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Has the needle ever been off the cluster?
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Old 05-14-2008, 01:32 PM   #7
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Quote:
Originally Posted by kotomile View Post
Has the needle ever been off the cluster?

dunno, owned the car 3 months as opposed to the last one of 13 years.
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Old 05-14-2008, 01:35 PM   #8
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Probably not since she was all stock when you got her. Mine used to read slightly lower before I swapped the faces out.
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Old 05-14-2008, 01:53 PM   #9
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here's the text I'm referring to:

Quote:
I'm in a unique position to own four cars with the real OPG and was getting different readings out of all of them. My 90 would show almost zero at idle and then jump back and forth between 30 and 45PSI at 3K rpms. My 92 shows very high oil pressure, pegging the needle when cold and consistently reading 60PSI or more at 3K rpms. The 93 showed normal pressure when running but wouldn't drop back at idle. The 91 was the only one acting "normal".

This project started out of concern over the high oil pressure in the 92. I originally took it to a shop to hook up a mechanical gauge and they then verified the oil pressure was actually 45PSI, and not 60 as indicated, at 3K rpms. They charged me a half hour labor.

...

The good news is that all four of my cars read within a couple of pounds of each other. I also tested the sending units per the Mazda shop manual. It is just taking an OHM meter and measure the changing resistance coming from the single metal tab on the sending unit at various rpms. My 90 tested bad – 52 ohms at idle and it would keep rapidly jumping back and forth between other readings (30 and 43ohms) under load. The other cars tested good and so I’ve made the assumption it’s in the gauge. The range of ohms is 52 (zero PSI) to 16 (90+ PSI) with what appears to be an infinite number between those ranges.

...

I suspect this is one of the reasons Mazda discontinued the real oil pressure gauge. Owners would complain over varying oil pressure readings and obviously now that the cars are getting some substantial age on them, the problem is being exacerbated by time and use.
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Old 05-14-2008, 02:02 PM   #10
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Anyone know how much a sender and gauge go for from the dealer?
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Old 05-14-2008, 02:08 PM   #11
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more than it's worth. I have the sender that came out of it, and an autometer one. I'm not concerned about the accuracy, just the precision. As long as I know the scale is just off, im fine. If I'm really seeing like 10psi at idle, that has me worried, and this motor finally doesn't leak or burn oil
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Old 05-14-2008, 02:43 PM   #12
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So tweak the needle a bit.

Edit: Have you checked oil pressure with a known working gauge?
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Old 05-14-2008, 02:49 PM   #13
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heh... it's been so long since i've had an oil pres guage in my cluster that's been anything but just pegged all the time...

it used to work intermitantly...
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