I bought a scan gauge 2 last fall and began monitoring coolant temperatures and it seems to me that my engine is running much hotter than I think is healthy, however not technically overheating.

In ambient temperatures of 20°C to 35°C it will warm up to the Tstat opening temp (82°C) fairly quickly and stay there until I get into traffic. Once Im in traffic it will slowly climb up. If it’s immediately into the highway and 100kph, it will stay around 83°C, but in town, even light city driving with a few stop lights it will get to 95-98°C pretty fast.

In many weeks now of monitoring the engine temp, most of the time it’s in the mid-high 90s, (mid to high 80s at night when the temp is below 20°C). The cooling fans kick on at 98-99 and do a pretty consistent job of bringing the temps down to 92....briefly, until the fans shut off again. This seems to me to be way too hot for the very low load/light throttle that the engine is seeing. I’d be much more comfortable with it staying around 90.

Im looking into versa tuner for the ability to control the fans, but I’m wondering more about the radiator itself.

1-Are these temperatures for the given ambient temps and driving conditions considered normal or acceptable?

2-If not, what would be my best course of action to reduce engine temps? Remove the plastic airbox tray or go full AEM intake? Upgrade to Koyo or CSF rad? Fans seem to be functioning to my knowledge.
Yes the plastic undertray is in place and I’ve already replaced the bottom foam and zip tied it up so it won’t sag again.

Thanks for the responses!

 

have you tried searching?


factory high fans turn on at ~210f(~98c)

 

Yep I’ve done nothing but search for the last 2 years. It’s remarkable how much harder it is to find good info on this forum compared to RX7club.

I know the fan’s kick on at 98.

I’m trying to determine if mid-to-high 90s while moving (30-70 kph) is considered normal/acceptable. Regardless, I’d like to try to get that number down to maybe high 80s to low 90s for the same conditions. That way when I do decide to give it a thrashing, I’m not starting at the brink of overheating.

 

There's a ton of variables to what your asking.

Lets start with the car it's self what's all done to it? stock cooling system? fans, rad, t-stat, age of the coolant. in stock form the cooling system is more than sufficient.
Next what are the driving conditions? do you have the AC on? engine rpm?

For me when it's 80-85F outside my car sits 175-190F no AC 200-205F with AC

I have upgraded the entire cooling system, fans(fal fans and a lower turn on temp), rad, t-stat, water pump, etc. and I'm only a few deg cooler than stock.

Sometimes ignorance is bills. If you spend to much time worrying about the coolant temp which is constantly fluctuating you'll forget to enjoy driving the car.

(tldr: any temp under 220f and you're fine)

 

Coolant efficiency is all about the condition of the wetted (inside) heat transfer surface, condition of the radiator, AND the pressure that the coolant is under (to prevent localized boiling that prevent localized heat transfer). Essentially your coolant system must be as clean as possible, flow properly, and be at target pressure. See here https://www.rx8club.com/showthread.p...82#post4828082 or down below.

 

Everything cooling system-wise is stock and hasn’t been replaced for at least 2 years (since I bought the car). Admittedly, the coolant old is probably due for a flush and change and maybe doing the tstat at the same time isn’t a bad idea.

Driving conditions are generally with AC on, but even with AC off the temps maybe drop
by 5C at most (unless on the highway, where it’s 83C regardless). Revs in town are under 4k except after a red light. I’m certainly not winding it up to 8k while doing 60kph, and when I have done that the temps go up pretty fast.

But that is good advice to not worry about the temps too much...I’d just like to not have to worry.

 

Look into a cooling fan control kit.
It kick the fans into high speed at a lower temperature. Its the cheapest mod for somewhat more piece of mind.
Also some new coolant might make your 8 love you more

 

All of this sounds fine. I don't see a problem.

 

While the consensus on this forum is that 220 or so degrees F at the ECT sensor is the max, and anything below that is acceptable, my personal feeling is that if your car cannot maintain thermostat temperature in normal driving, then the cooling system is inadequate. Unfortunately, this car as built has inadequate capacity in my opinion. If you are at 220 degress F at the ECT, there are coolant passages at 260-270. Mazda has stated that 236f or something is max in some tech literature. That's great, but that also doesn't mean you want to spend time there. I cannot see how consistently high temps, and large temp variance is good for any engine, much less this one. If longevity is your aim, do what you need to keep it at thermostat temp all the time. That is the design temperature of the engine, not the fan switch temp, and not the max temp of the coolant seals.

 

Traffic and slow city driving in 30C+ with AC on leads to heatsoak, it's not unusual. You can certainly upgrade the rad and fans if you like, but again, 98C (208F?) is not particularly worrying if that's where it stays. If it creeps ever higher, your system is actually not coping. The fan relay kit should help with that since that's what's pushing air through the rad at slow speed.