Here’s a quick post showing the differences between the two NA Miata oil gauges. As you may know, the 89-94 cars got working oil gauges that actually report oil pressure. The 95-97s got dummy gauges that only show “some” pressure when the sensor reads anything above 7 psi.
This is not new information, but I was hard pressed to actually find a detailed write-up of this a couple weeks ago. I found some forum posts where some “expert” replied that a photo of the back of a gauge was “definitely the real one” but couldn’t find anything concrete.
This post will produce concrete.
This IS indeed good news. Take a look. ALL of the faces minus one came from real oil pressure gauges (called OPGs for the rest of this post). This is from my collection in the shop. As you may know, I make gauge faces and often do installs.
I was actually surprised at this photo. Just one out of… apparently 8, was a fake face. And that holds up to my data with orders – there are a lot more NA6 Miatas out there (that’s 89-93) than NA8s. Mazda just produced more.
That said, the face doesn’t guarantee that you have a real, working OPG.
In the above photo, there’s ONE fake oil pressure gauge. The others are real. And, aside from the one with the face in the photo, they’re all identical. You can’t look at a photo of the back of one of these gauges and determine which is which. The board layout is the same and the color of the board is meaningless.
Let me say that again – the back view of the gauge doesn’t tell you which gauge you have.
As for the face, I once purchased a “real” oil pressure gauge with the correct OEM face. It turned out to be a dummy gauge. This was about a decade ago, but I still remember and get angry thinking about it.
The best way to tell the difference is by reading the resistors. They’re different on the real and dummy gauges.
Real – as viewed from the front.
Left: blue, red, black (62 ohm, I believe)
Right: green, brown, black (51 ohm, I think).
And both sides have the gold band on the end which means 5% tolerance.
Dummy – as viewed from the front.
Left: brown, black, brown (100 ohm, possibly)
Right: grey, red, black (82 ohm, maybe)
And the dummy also has the 5% (gold band) resistors.
SO. That’s what you need to know. You need to see the resistor values to determine if the gauge is a working OPG or a dummy OPG.
But we can take it a step further.
All you need is a desktop power supply and you can see the difference in the gauge function for yourself. Just wire power to the “+” terminal, ground to the “-” terminal, and the “U” terminal is signal. Grounding it will show the gauge’s behavior.
When the real gauge receives a ground signal, it rockets up to 90 psi.
When the fake gauge receives ground, it drops – very slowly – to 0 psi.
And there you have it. Everything you ever wanted to know about Miata oil pressure gauges.
So… Theoretically then, one could change the resistor to the correct value and then have a correctly working oil gauge?
No. Clubroadster came up with the same question.
Watch the video and see the gauge behavior when power is applied. One rockets to 90 psi. The other drops to 0. The windings on the gauges are reversed.
It might be possible to just reverse polarity. If you did that, removed the damping grease, and swapped resistors, you MIGHT have a “working” oil gauge. Then you’d just need the early sensor.
Or you could spend $20 and get a used working gauge. They’re extremely plentiful.
If i swap the gauges do i need to also swap the sender to end up with a function OPG?
Yes. You need a matching sensor to go with the gauge. The dummy gauge also has a dummy sensor, that’s really just a switch.
What about oil pressure gauges on an NB? I don’t suppose its possible to fit an early NA gauge to those cars, is it?
Yes, it has been done by at least one person to my knowledge.
It IS possible, but I understand it’s a hell of a lot of work. M.net has instructions.
Scroll down to the Drake Daum section.
Another great post, Adam. I’ll have to make the swap when I install my new dash top.
Another highly informative post that answered a question that I couldn’t find any definitive info on. Thanks for taking the time to put this together! Any speculation on if the temp gauge is similar (ie. will a 90-93 temp gauge and sender swapped into a 94-97 work)?
The temp gauge is also pretty different. Different resistors in a different layout. When folks swap their clusters they usually have to keep the tach and temp gauges that belonged to their car originally. Both have some internal differences.
[…] faces on. Since you're in a "check all the things!" mode anyway… Check this first: Miata Oil Gauge – Real vs Fake — revlimiter.net Your signal wire is the one you just fixed going to the relay. That gives your gauge a clean bill […]
This is an awesome How To to tell the difference between them. I have 2 spare clusters that I am going to tear apart now and test the gauges to see if I have a real or a fake. Will I still need a new sender if I install a real one? I feel like I will..
Yes, the sender and gauge have to match.
Dummy gauge + dummy sensor (or VDO sensor) = happy.
NA6 gauge + NA6 sensor = happy.
I don’t understand…
I got a TDR kit
And my gauge is working nicely.
Am I missing something ?
Yup. I used to have that one. My gauge had resolution between about the 30 mark and just above the 60. Not much more than that. Just a little bit of a twitch between full pressure and no pressure.
With the NA6 calibrated and matched gauge and sender, you get resolution from 0 all the way up to 90. And it’s calibrated from the factory.
Did I mention it’s calibrated?
Does the 95M have a real oil pressure gauge?
No. Sorry. The real gauges ended in 94.
(2 years after the most recent post, but…)
Where might one reliably find a matching NA6 pair?
I wondered if you could help. NC with paddle shift auto. There are lights showing the gear selection in the dashboard. The bottom light – the “m” when using the manual gear paddles no longer works. Dealer tells me to buy new circuit board at well over $1000.
It failed gradually. Usable for some time but at about quarter brightness and finally went out.
Is there anything I could do to restore the light?
Hoping you can help.
Tasmania – Australia