I took my FD on a 500 mile trip this weekend in the Texas summer heat. I've never taken it on that long of a drive before or driven it that long in this heat (>100ºF) and I saw coolant temps on my PowerFC commander that made me uncomfortable. After about an hour of highway cruising at 3k RPM my coolant temp hit 94ºC, and then I hit stop-and-go traffic where it spiked to 101ºC and hovered between 98º and 101º the rest of the drive (another 2 hours). I had to stay out of boost entirely or temps spiked, and the only thing that seemed to help was lower RPM like throwing the car in neutral.

I got home and let the car idle in the shade with the hood up and a leaf blower over the radiator until it got down to 87º, but when I parked everything under the hood was so hot I couldn't even touch the hood prop rod with my bare hands. The whole car just smelled hot.

Is this normal in these conditions? Are these temperatures something I need to be worried about?

I have a PowerFC, BNR stage 3 turbos, used Koyo radiator and 6k miles on my engine. Last coolant flush was probably close to a year ago and I replaced the radiator hoses at that time.

 

Those temps sound normal for hot weather. I think a TT rotary running hot is just the nature of the beast.

 

its not even hot, fans turn on 105c
https://www.rx7club.com/3rd-generati...system-906142/

 

My car is mostly stock, and the hood prop gets too hot to touch after an hour or 2 of normal driving on a summer day. Not sure about your mods, but on a stock car, setting the cabin fan to 3 or 4, or turning on the running lights kicks up the idle a little and turns on the radiator fans continuously. It's enough to keep the engine a little cooler, especially helpful in traffic.

 

Thanks for confirming. I lost the engine to a coolant seal failure years ago and have been nervous about it ever since. I never see temps over 100º so wanted to check before it happens again.

On my PowerFC settings fans turn on between 82 and 87ºC, so they were running full blast the whole time and this is just the best they could do. I think under boost I easily could have gotten close to 110º.

What temp should I actually start worrying about?

 

This is probably obvious, but you have a downpipe, right? My summer temps were much higher when I still had the stock pre-cat installed. Regarding what is too hot, this thread may help:

https://www.rx7club.com/3rd-generati...thread-571088/

 

Yes I have a downpipe and vented hood as well (Mazdaspeed)

 

hate to be the one to disagree but your car got hot. relatively speaking it was still "cool" but for your set up it definitely got hot. i would suggest checking your pressure cap for wear or just replacing entirely if you dont know how old it is. hopefully youre not running an AST. what is your oil cooler situation?

 

Out of curiosity what was the ambient temperature?

Many moons ago I was going home mid afternoon through the backside of LA (inland empire). It was a very hot day, in LA where I was earlier was like 105°F. My car temps were fine all day right at mid section of the temp gauge. Anyway, I was cruising in the freeway through this valley when I noticed my stock temp gauge at 3/4 to H (that's like 115°C). Mind you I had my car for a few years already and I had never seen that before (nor since). I immediately rolled down my windows, turned off the AC, and turned on the heater. That worked, the temp gauge settled back down to middle. Once I was out of the valley, with 100 miles or so still left on my trip I rolled my windows back up and turned on the AC. The temp gauge never moved proving my car didn't all the sudden developed a problem. What I assessed that the heat in that valley must have been crazy high and so my system could not keep up.

Anyway, the moral of this story is that at the end of the day we are all slaves to whatever the ambient temperature is.

 

Ambient was about 104º and I was in full sun the whole way. AC was on full blast the whole drive too, though turning it off didn't seem to do anything.

I guess I am worried about nothing. If my car can run the AC and keep the coolant temp under 100ºC in punishing conditions for several hours without a break, I am probably in good shape with all the work I've done to this car

 

Pressure cap was brand new as of a few years ago. Same with the water pump and thermostat. I do have an aluminum AST and the r2 dual oil coolers

 

Sounds about normal for running the A/C with your mods.

If you're still on the single oil cooler in the touring model; coolant temps would improve quite a bit with dual oil coolers.

 

You are totally fine. Think about it, your car was within operating conditions in grueling heat of 104°F. You just didn't like the number because it's higher than you're used to that's all. Next time turn on the heater. It should help as it extracts heat from your engine (it's just no pleasant tho ).

 

^Agreed. I don’t think any of your reported temps are unusual for the conditions and running A/C. Assuming you have the common 50/50 mix, the only other thing I can think of that might mediate things is to run at least temporarily a higher water to coolant ratio. I’d just keep, say 10 % or 15 % to control corrosion.

 

Remember, the stock fan switch doesn't kick on until 107 deg. F. Stock cars would ROUTINELY get that hot. Of course that's probably not amazing for coolant seals.

That said, if you don't have an FC thermo switch I would recommend getting one. Drops one of the fan inputs from 107 to 97 deg. C. Without that you will never hit "high" speed on the fans until 107. The ECU controls one fan input and the AC controls another.

Also I assume you have the belly pan on the car. Also worth seeing if you need foam around the radiator to seal the edges, you want to force air through the radiator. If there's a large gap you will have a lot of air going through the gap and not the radiator, it takes the path of least resistance.

With the insane summer temps we've been having (and will have in the future) cooling mods are becoming more of a Must Do for sure.

Dale

 

IIRC from what I’ve read the stock coolant seals are typically good to about 115 C. (240 F.) before they start to degrade.

 

I thought this mod was only for the factory ECM. Can the PowerFC not control the fans entirely? I know I have 3 fan settings in FCEdit but I don't remember exactly what they are. If there is a setting I can't control and which won't allow fans to fully come on under 107º I'll absolutely do that upgrade

 

The 93-95 ECU only controls 1 fan input. AC and thermo switch do the other 2.

This isn't a PFC thing, it's how the 93-95 cars were designed. Later cars got rid of the fan thermo switch and had the ECU control 2 of the speeds. That's why the Datalogit shows more than 1 fan speed - that's for the later PFC's for the later versions of the FD.

In other words, not a PFC issue, it's a "how Mazda wired it" issue.

Dale

 

Lol, I did that exact same thing once... and then I was like...ok, this is being a bit too cautious lol.

 

I live in Houston, and this is my setup for cooler water temps.

1, Koyo N pass radiator.
2. 75% distilled water, 25% antifreeze, 1 bottle Water Wetter,
3. SARD SST12 thermostat
4. In the PFC, Settings 3, Fan vs Water Temp: 81C for summer, 87C for winter.
5. Added aluminum sheet air flow diverters to keep air flow from leaking out the sides of the radiator inlet.
6. Single shark tooth inlet expanded-er.
7. If you have those front fog lights, remove them. Also remove those corner plastic pieces.
8. Raise front plate holder.

 

Pretty much how I run in South FL except the shark tooth mod. Is that on your build? I don't think I have seen the "single".
been considering a 99 front or similar, but i start debating to sell or not and I put it on hold lol...

 

Back in the 90s, there was a small Florida company called N-Tech which made the first boxes to hold a small PC680 Odyssey battery to replace the stock battery.
Later they came out with the shark tooth mod. I copied their mod.

One cooling mod I forgot to mention: the cooling fan switch mod to increase fan speeds 1&2 to 2&3.

 

i do have a mazmart "upgraded" water pump also.

I am considering a new front all together. Like a 99 spec or similar. I want to let my oil coolers have a bit more volume and still want that vented hood!