making the "oil pressure gauge" into a true gauge
 

does anyone know how to do that? i think it would be useful, as long as i knew what was normal for driving and what was a sign of possible damage to the engine
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The May issue of Sports Car International reviewed an RX-8 in Thailand and
said that the car had an oil _temperature_ gauge.
That would be a nice way to use that spot, as long as there is an idiot light
for a complete lack of oil pressure.

Echo'ing POOMan, does anyone know how to convert the existing idiot gauge
to something more useful?

Really, all you need for oil pressure is an idiot light. On the RX-7 (specifically the 2nd gens) the oil pressure is 30psi at idle, 60 psi at 3000 RPMs and up. That's as exciting as it gets. If it drops down significantly, there's a problem.

The oil pressure doesn't really fluctuate much if at all.

Of the 50-some 2nd gens I've worked on (and done about 10-15 engine rebuilds) and 10-15 3rd gens I've worked on, I've seen VERY few oil pressure problems. The only problems I've ever seen are -

- Bad oil pressure sender (very common on the 3rd gen, they had a flaky one, the 2nd gen senders are solid)

- Bad thermopellet in the front of the eccentric shaft. This keeps the front rotor from getting oil when cold to accelerate warmup, but has a tendency to fail. Numerous people make CNC'd plugs that bypass that system, which fixes the problem and removes a potential problem spot.

- Damaged O-ring between front cover and engine. This is typically due to a novice rebuilding an engine and choosing the wrong O-ring or having the O-ring crushed. Output from the oil pump is bled off, resulting in 15psi/45psi oil pressure pattern, which is still not low enough to cause damage :).

That's about it. I've NEVER seen an engine that failed due to some sort of oil pressure problem, or even had less than optimal performance or the like. The primary causes of engine failure/need to rebuild are -

- Overheating. This is BAD NEWS. Overheat a rotary, you warp the housings, compromise the water seals, and end up with an engine with ZERO reusable parts. I've torn down engines that needed a CHISEL to get the side seals out of the rotors - these normally fall out during disassembly!

- Detonation. Severe detonation will break apex seals, causing a loss of compression. Normally it's the rear rotor that goes - the tip of the apex seal breaks off, scuffs the rotor housing, and imbeds itself in the rotor. New rotor and rotor housing, new seals, and the engine is good to go.

- Carbon lock. Use cheap oil, gimp the car around at low RPM's all the time, and you're gonna build up a LOT of carbon on the rotors. Over time, it can get bad enough that it can make the seals stick in the slots, causing compression loss, or have a hunk of carbon break off, causing damage to the rotor and apex seal. Typically some serious cleaning and maybe a new rotor/rotor housing and seals are needed.

- Broken dowel pin seat. This is in the rear iron, near the oil filter - there are dowel pins running through the rotors that add torsional stiffness to the motor. On VERY high output motors (350+ horsepower) or from prolonged detonation, the shock loading and twisting of the engine can cause a crack to form in the dowel pin seat in the rear iron. This calls for a new rear iron, and probably some other parts that were damaged by detonation.

I would moreso look to see if the water temp gauge is linear or an "idiot light" - the 3rd gen's water temp gauge was an idiot light, and if it got up to about 3/4 you were already in engine damage territory. That's why one of the VERY first mods on a 3rd gen is either linearizing the stock temp gauge or installing an aftermarket temp gauge.

Dale

I did it on my NC MX-5. Removed the OE stepper motor, put analogue motor in place and wired to actual sender installed in place of OE Pressure switch. Had to make them fit and buy the smallest sender and display motor I could find. But it worked