OK, here's the deal -

The '89-91 2nd gen RX-7 and the 93-95 3rd gen RX-7 had "idiot light" temperature gauges. Let me explain this concept.

There is a wide range of input from the temp sender that's considered "normal" temperature - I believe from about 170 deg. F to around 230 deg. F Anywhere in that water temp range, the gauge will just sit at the middle. This is a Bad Thing. If the gauge starts moving off the middle, you're already in a dangerous overheat zone, with engine damage VERY likely to follow.

Mazda, everyone has assumed, changed the temp gauge to an idiot light to reduce customer complaints. Basically, people wouldn't bring their car in when the gauge went a little way up than normal.

From what I've seen, it's VERY likely they continued this trend on the RX-8. This is a BAD THING - one thing that gave the 3rd gen RX-7 such a bad rap was motor problems, many of which were caused by overheating.

Had the owner/driver known that the car was starting to exhibit symptoms of overheating due to a stuck thermostat, coolant leak, or the like, I believe MANY engines could have been saved, as well as the reliability reputation of the 3rd gen. Matter of fact, installing a temp gauge or "linearizing" the stock temp gauge is considered one of the very first mods to do on a 3rd gen.

Here's what we need to do -

First, determine if this is the case on the RX-8. One potentially easy way to do so is if the diagnostic mode that was just posted works -
http://www.mustangworld.com/ourpics/News/99hec.htm

It's a standard OBDII diagnostics mode, and that method works on the Mazda 6. I believe you can view water temp in degrees - if so, that will correlate what the temp gauge is saying and what the actual temperature is.

Any other method will require some minor hacking - either installing an aftermarket temp gauge, or attaching a variable input to the stock temp gauge to find it's range. Many people probably aren't ready to do that on a brand-new car, however.

Regardless, the point is - if Mazda *did* use a non-linear temp gauge, we can ask them to make a production line change to the instrument cluster. The change would likely be VERY simple for the instrument cluster supplier to do - the mod to make a 3rd gen gauge linear was adding a simple jumper wire.

What do you guys think?

Dale

The Diagnostic mode DOES work. I tried it in the parking lot at work. Didn't have time to really noodle around with it though. One thing I noticed that the oil pressure guage maxed out at the point where it normally sits when my car is idling. That just doesn't sound very responsive...More later

Originally posted by B-Nez
One thing I noticed that the oil pressure guage maxed out at the point where it normally sits when my car is idling. That just doesn't sound very responsive...More later I don't know about the temp gauge, but the oil pressure gauge is an idiot gauge on the RX-8; the gauge will always either read 0 or middle of the scale.

The oil pressure gauge being an idiot light is fine - oil pressure just isn't that big a deal on the rotary. In all the years I've worked on RX-7's, and all the engines I've rebuilt, I've YET to see one that had damage from low oil pressure.

Really, you only need idiot light feedback on oil pressure to begin with. If it's lower than 30psi at idle, then there's something to look into. But, there's really not a lot of things that can cause low oil pressure - most common is a failed eccentric shaft thermo pellet. Every other part of the oiling system (oil pump, bypass valve, oil pressure regulator) has proven itself to be VERY hardy and reliable - I've yet to see a failure.

Now, water temp failures are a whole 'nuther story!

Dale

Both the Temp and Oil 'gauges' on my truck are 'idiot lights'. Supposedly, Ford did this because of customer complaints about gauges not reading in the proper zone (engines running too hot or cold, and oil pressure drops at idle). My understanding is the oil 'gauge' only shows zero if the pressure is below 5lbs.! If the RX-8 is the same then that is bad.

We don't know *for sure* if the RX-8's oil pressure gauge reads "bad" at below 5psi. Hell, I had a bad front cover O-ring in my '88 Turbo for some time, making about 10-15psi at idle, with NO ill affects. Low oil pressure on a rotary isn't an "engine killer" like on a piston - the engine spins, instead of having the up and down load on the bearings.

Anyhow, we're straying off topic. THE IDIOT LIGHT TEMP GAUGE IS AN ENGINE KILLER! If we can determine that this is the case, then we need to present an argument to Mazda. The rotary community didn't have the chance while the 3rd gen was still in production to address the problem with Mazda - with the RX-8 just beginning production, now's the time.

Dale