Hi guys,

I've had my '04 RX8, 6 speed manual 6 port engine, for about two years. It has performed flawlessly in that time. Currently has 70k miles and it has started to move the temp gauge past half way only under heavy load. The first time was on a longer highway trip for about 300 miles. About 60 miles in I pulled over for a pit stop for two minutes. When I pulled away again I redlined 1st, 2nd and almost to redline in 3rd. Temp needle started moving past half way. So I clutched in, grabbed 6th gear and slowed down to 65mph the temp level came down to normal level immediately. I encountered the same thing the next day when climbing a steep hill behind some traffic, as I was nearing the top, the temp needle started to move a few notches past half way, I got to the top and it was a few more past half way, but still short of 3/4. The temp then went back to normal for the rest of the journey which was a flat 300 miles.
It has done it once more to me this week joining the highway at 60mph, 3rd gear accelerating and it started moving past half way.

I have had the coolant system pressure tested, no leaks. Radiator flows 100%. Thermostat operates as it should. Both fans work. Doesn't use or leak any coolant and the birdcage works as it should and I haven't seen it light up. You can drive the car in heavy traffic and the needle stays bang on just under half on the gauge.

The car starts perfectly. Hot or cold. In fact I can't flood it. I can turn it off dead cold and it starts first crank. No smoke at idle.

Fuel consumption is pretty terrible though. I'm averaging about 14mpg.

Is my engine shot?

Thanks.

PS sorry for the novel

 

Did you check the water pump? It seems like you only over heat when flooring from idle. That sort of leads to your fans. Your temps go up when idling, but not high enough to overheat. Flooring immediately after that causes the coolant temp to go higher than that, and then the needle moves. When you cruise at 60mph, there's sufficient air going through the radiator to keep things cool, so you don't over heat.

If you're sure the thermostat is fine, the radiator works as it should, and there are no leaks in the system, my bet is its the water pump or the fans.

 

Ok, both fans are working though.

Wouldn't a bad waterpump make it overheat all the time?

Oh front under tray is in place and intact as well.

 

One word ....... three things . Foam !

 

I need data logs to remotely diagnose your situation. What you are saying about the temp gauge is troubling, however. It doesn't move from the center until you are already very hot (235F if memory serves). That points to overall inefficiency in your cooling system that could be due to one big failure or several small failures combined. My coolant temp never rises to more than 215F on the track in the hot Texas summer. Under normal spirited driving around town, it never rises much over 195F.

Fans
The fans in this car are known to weaken (slow down) over time. Yours are 12 years old, so they are worth testing for RPM and current draw.

Water Pump
The early water pump design was known to suffer from cavitation at high RPM. Mazmart solved this with their aftermarket Remedy water pump, and Mazda redesigned their pump at some point. So, again, at 12 years old, yours is worth looking at, as it could be the early inefficient design.

Radiator Foam
The radiator should have some heavy foam on the bottom and light foam around the top and sides. The foam is designed to force more air through the radiator and low speeds and allow some air into the engine compartment at higher speeds. Some guys advocate stuffing more foam all around the radiator to force as much air as possible through it. It will lower your coolant temps when the car is moving, but it will also raise your engine compartment temps, which is not good for the rubber and plastic in the engine bay. If everything else is working well in your cooling system, this treatment should not be necessary, IMHO.

Radiator
The proximity of our radiator to the ground means it gets dirty faster than radiators otherwise do in other cars. I have found back-flushing the fins with clean water to be worthwhile. Clean the oil coolers while you are at it. And, be sure to straighten all the bent fins you find in the process.

Thermostat
In a 12 year old car, the thermostat may not be opening completely. It is an inexpensive part that is relatively easy to change. You also have the option of buying an aftermarket 170 degree thermostat that will begin to open 10 degrees sooner to help combat heat soak.

Catalytic Converter
What? Seriously. The cat is prone to clogging and preventing heat from effectively escaping the engine. This can put additional strain on the cooling system. It should be inspected.

If it were my car and my wallet, I would bite the bullet and refresh the whole cooling system just to be sure. I would replace the radiator since it is partly made of 12 year old plastic (an OEM style replacement is only $90), replace the water pump with an OEM unit, replace the thermostat with an OEM or Mazmart 170 degree unit, replace the accessory belts, and flush and replace the coolant with genuine Mazda FL22. I would test the fans and replace if necessary. I would also inspect the cat for any signs of clogging.

.

 

^ this!

Everything you need to know is here.

The fans might be spinning, but are they spinning fast enough? Like Steve said, they are known to slow down over time. You'll never tell by hearing them because even when they're slow, they're pretty loud.

Get a cheap OBD2 scanner for $5 from eBay and pair it with an android phone using the Torque (free) app. Get a log file of the coolant temp and post it here.

 

I also wonder if all shops that do flushes on Renesis engines are aware of the FL22 Coolant.
I do not know for a fact, but I have read on the forum several times that our 8s WILL run hotter on non FL22 coolant.

 

Does anyone know which is fan 1 and which is fan 2?