Miata Oil Pressure Gauge

The early Miatas ('90 through '94) were built with genuine, working oil pressure gauges. It had real PSI markings and the needle actually indicated the oil pressure of your engine. In '94, Mazda replaced the gauge with an "idiot gauge" which looks like an oil pressure gauge, but in reality only has two possible needle positions - just like a light but less useful since it gives the false impression of showing a reading. The good news is that it can be replaced with an earlier gauge to give genuine oil pressure readouts.

David Gould (dg@illustra.com) gave us this procedure to do the retrofit.

I have both a 91 and just got a 95. I like the 95 better except that the oil pressure gauge has had a lobotomy. It is really just an idiot light with a needle instead of a bulb. Just in case anyone else wants to do this, it is possible to put the real gauge in a later car.

You need two parts:

You might want to try for a sender and gauge from a wrecking yard since dealer prices will be even higher.

Following the procedure in the shop manual take the instruments out of the dash, unscrew the gauge, replace it with the new gauge and put the panel back in. This is easier than it appears and only took about 1/2 hour.

Unplug the sender lead and unscrew the old sender (switch) from the side of the engine. Put some silicone seal on the threads of the new pressure sensor, screw it into the block, and plug in the sender lead. Start the motor and look for leaks. The manual describes this too.

You will need a 24 mm and a 29 mm socket to do the unscrewing and screwing respectively. It will help if the 22 mm is a deep socket. It will also help to put the car on stands and remove the right front wheel. Torque spec for the sender is 13 ft/lb but there is no way you will get a torque wrench in there, so just make it 'not too tight'.

Getting the old sender out of the engine is not easy without a trained octopus to reach in since it is even harder to reach than the oil filter. It is also hard to unplug the sender lead since you need to squeeze it and it is hard to get a grip. Pliers helped. This whole step took more like 2 hours since I kept dropping parts and wrenches down in the car and wiggleing around trying to get a better reach and generally having problems.

But, I now have a REAL oil pressure gauge! Probably not worth the effort, but maybe easier than plumbing one in from scratch.

Leon Van Dommelen adds some tips to the above at http://www.dommelen.net/miata/goodies/oil.htm  

Drake Daum was frustrated with his '99 retrofit. He managed to do it, but from his writeup, it doesn't sound like something we would recommend.

RETROFIT OF EARLY M1 OIL PRESSURE GAUGE TO THE 1999 MIATA INSTRUMENT CLUSTER

Since the introduction of the 1995 Miata, Mazda's oil pressure "gauge of choice" has been the infamous FAUX gauge. Mazda has chosen to save a few bucks per car and quit installing REAL oil pressure gauges. Instead, there is a binary, on/off idiot gauge that merely tells you, "Yes, Virginia, there is SOME oil pressure."

This on/off switch is activated by oil pressure (at a very low threshhold value, I might add). When the car's running, the gauge needle goes to a fixed position and stays there until the on/off sender switch ceases to sense oil pressure when the engine is turned off. There is no needle fluctuation regardless of engine RPM.

Mazda used a REAL differential analog oil pressure gauge system (sender unit AND dash gauge) from 1990 through the 1994 model year. 1990-1993 cars were equipped with the 1.6L engine. The ONLY 1.8L car equipped with the correct oil pressure instrumentation was the 1994 model year.

My wife Cinda and I recently adopted a silver 1999 Miata to keep our supercharged red '92 company. I quickly formed a long list of modifications and accessories I wanted to perform on the '99 and changing the oil pressure gauge was at the top of the heap.

This turned out to NOT be a trivial job. Mazda has changed so much on the new 1.8:L engine and especially the 1999 instrument panel.

The mod was more trouble that it really needed to be. The really frustrating part was mounting and wiring in the old gauge in the 1999 instrument cluster. It shouldn't have been this hard. There was no need for Mazda to make things so tough by completely remolding the interior of the plastic instrument shell. NOTHING mates up the same way as the M1 cluster. It all has to custom installed and wired.

The pressure transducer sending unit on the engine is much easier. Although it is necessary to use seveal small brass fittings (I think they are 1/4 pipe thread -- an elbow and a short straight piece), the installation of the sender is straightforward. To make for easier during installaiton, I removed the under-engine plastic belly pan so I could gain good access to the right side of the engine. The oil pressure port is located at the 11 o'clock positon in reference to the oil filter.

The reason I selected the components from the 1994 car was because I was installing the items on my 1999, which is also a 1.8L engine. Not knowing what difficulties I was about to encounter, I figured I may as well hedge my bets and start the project by trying to retrofit parts that were originally installed on another 1.8L engine. I would bet that the sender unit and dash gauge from the earlier year cars woiuld also work, but these parts may have more mileage on them and the dash gauge may have more exposure to sunlight.

(Yes, it is necessary to retrofit BOTH the sender unit AND the dash gauge -- one or the other will not work by itself.)

The oil sender unit for the 1995 and later cars is a very small unit about the size of a quarter and only about a 1/2 inch long. The REAL differential sender unit is about 1-1/2" in diameter and about 3 inches long. It is NOT a direct replacement, because there is interference with adjacent engine components in the area where the sender screws into the oil journal on the 1.8 block. It is necessary to replumb the sender with some brass fittings to attain mounting clearance. The attachment wire then needs to be lengthened to reach the single connector on the end of the sender unit.

The internal configuration of the 1999 instrument cluster is vastly different from the M1 cars. The gauges mount differently, are connected to the printed circuit board differently, and the gauge face attachment pins are all in different places. Not to mention the finish on the gauge faces now has a purplish-black sharkskin appearance, whereas the M1 gauge faces are flat black.

To mount the 1994 oil pressure gauge in the 1999 instrument cluster, I had to remove the three hexagonal mounting lugs on the back of the 1994 gauge to gain the necessary clearance to seat the gauge in the cluster. Since the electrical contacts on the 1994 gauge are almost exactly opposite that of the 1999 printed circuit board, I had to physically attach 3 small wires to the back of the gauge and attach them individually to the circuit board.

Further modification had to be done to the clear plastic light transmission pieces on the backs of both the 1994 oil pressure gauge and the 1999 speedometer. Both had to be placed out on the workbench to perform surgery via a Dremel tool.

Final mounting of the oil pressure gauge had to be done via clear RTV sealant because there was no practical method of mechanically attaching the gauge to the 1999 instrument cluster. Fortunately, the back of the 1999 instrument bezel has a ring of plastic around all three small instrument holes that extends rearward and presses on the faces of the oil, temp, and fuel gauges. This feature helps to hold the 1994 oil pressure gauge in place till the RTV sets up. It is necessary to be very careful to position the gauge in exactly the center of the bezel opening to avoid the look of an off-center gauge face when everything is reassembled.

Although very pleased with the result, it took me ALL day to do this work. Not having any prior knowledge from another Miata owner for installation tips, I had to engineer this mod as I went along, stoppiing twice to go shag parts at my FLAPS. But now, by golly, I have a real, functioning oil pressure gauge in my 1999 car. Although the gauge face finish is different from the rest of the stock 1999 gauges, it is really not too apparent unless viewed in direct, harsh sunlight. And even then, I doubt anyone but a Miata hyper-enthusiast or Concours d'Elegance judge would notice the difference.

Having done this once, I'm not too sure I would want to tackle it again. It is not a bolt-on mod by any stretch of the imagination.. It is custom work all the way.

Drake Daum