I've got an awesome running third gen with 81k miles on it(mucho better than my dearly departed third gen which had the turbos go bad at 63k miles). The only problem that I'm currently having is that the coolant runs VERY hot. I've got an aftermarket electrical temp gauge/sensor installed and if I'm in stop and go traffic, temps easily get into the 230 degree F area. I've got the fan switch on my car and I rarely let the car get this hot. I usually switch on the fans (I've done the manual fan switch mod) at around 210 and the temp goes down to the 190-200 range within a couple of minutes regardless of how hard I'm driving. Although this is relatively safe, I'd really prefer not to have to stare at the temp gauge and turn the fans off and on all the time. Plus I don't think that the computer recognizes the extra electrical load of the fans when I turn them on manually. The rpms of the car drop approximately 100 rpm (idle goes from between 600-700 rpm to 500-600 rpm when I turn on the fan), which probably isn't "hurting" the car, but who really knows, these cars can be so finicky.


I recently bought a new OEM thermostat and gasket (they're relatively cheap at www.thepartsbin.com), but given the fact that the temp does go down when the fans are on, I'm kinda skeptical that the thermostat is the cause of the high heat. My former RX also had an aftermarket temp gauge and I don't think that I ever saw the temp go higher than 220 or so. So whadda ya guys think is the problem here? I figure that these are my options.


1. Replace the RX fan switch with that of a Miata (I've heard that they turn the fans on around 210 or so automatically). This seems to be the least intrusive option.

2. Replace the radiator with one of the all aluminum ones (Koyo, Fluidyne, MazdaComp, or SR) and the hoses that go to the radiator (with silicon ones from SAMCO, BTW Pegagus no longer carries this, does anybody know where I can buy?). This seems to be the most intrusive option.

3. Replace the thermostat and gasket. Relatively intrusive, does anybody know if I really have to remove the altenator and drain all the coolant to do this?

4. Replace the coolant pump with an electrical one (I may do this anyways since I don't think any other forum members have done this mod and it'd be a neat little project).

Any suggestions would be helpful.

Thanks!

 

Have you changed or checked you coolant lately??? You could have air in the system that needs to be let out. Have you checked for leaves and such stuck in the radiator? have you removed the spash guard thats under the engine? That splash guard helps funel the air thru the radiator.

I would check these things if you havent. If everyting is ok go have you radiator flushed out it might have goop in there clogging it up somewhere.

Later,
STEPHEN

 

I've changed the coolant out 2 times this summer (with a distilled water flush on both changes). The system is definitely air free. No leaves stuck in the radiator. Splash guard is installed. I've even tried Redline's Water Wetter and it made absolutely no difference.

BTW, If I'm running at a steady speed over 45 mph, I don't have to turn on the fans, temp stays under 210. It only gets REALLY hot in stop and go.

 

it doesn't sound like your car is getting overly hot. my car displays about the same behavior in terms of temperature. one thing you didn't tell us was where were the sensors located in your two rx-7s? in the stock location or near the water filler neck. anyway, i think your old rx-7 just ran exceptionally cool for a 3rd gen. in stop and go traffic just about all rx-7's are going to get hot just because of the insufficient cooling system and increased heat creation. as long as the temps don't go past 230 i wouldn't be too worried. if you still think there is a problem go and replace the thermostat first because it's cheap and easy. then replace the radiator if you want further cooling.

 

This sounds stupid but when your parking ligts are on and the computer sees this extra load it turns the fans on at 210 degrees instead of 220 or 230 thats what i do. I hope that helps a bit. Whatever you do to try to fix the problem start with the easy stuff first then move from there.

 

I've heard that 230 is testing your luck against detonation as well as possible apex and o-ring damage. I think that optimum operating temp of the RX is between 180-200, too low and the RX goes into cold mode. Too hot and you risk the above.

 

180 degree thermostat, Fluidyne radiator = cooler temps

 

With a completely stock setup, the fans turn on at 230 F. It is true that with the park lights on, they turn on at 212 F.

Obviously, Mazda designers felt it was okay for the engine to run at 230 F, or the fans would come on sooner. Now I'm not saying that it is a good idea to run it that hot very often, but it is normal for the system to act that way.

If it ever get any hotter than that, you definately have a problem. I have a Comp. Radiator and two oil coolers and have also seen those kinds of temps in stop-and-go traffic commonly on a hot day. The key to keeping things cool is to RUN WITH THE PARK LIGHTS ON all the time. That way it can turn on the fans automatically at 212 F.

Also, I have had to replace my thermostat twice in two years because it does not open all the way up! It is a very common problem, and nothing to mess around with. If it doesn't open all the way, coolant flow is reduced and the already undersized cooling system is not able to remove heat rapidly enough to keep up.

It is very easy to replace it. Take out the airbox and unbolt the water neck and there it is. You should put your current thermostat in hot water on the stove and see if it opens all the way. If not, replace it! They are cheap. Put the little "loose rivot" on top. I am told it helps remove air from the system.

Also, what H20/coolant mixture are you running? Water has more heat capacity, so use only about 20%-25% coolant in the mixture.

This all just goes to show what those without aftermarket temp. gauges are missing out on.
The stock gauge doesn't even move until around 240 F !!!!!
At least you are able to monitor what is really happening. Most people who overheat their cars don't even know what's happening.

Good luck!
Jeff

 

I just got a Fluidyne and new thermostat, and now the car runs exceptionally cool. It basically stays right at 180 whenever the car is moving, if I sit and idle, it will slowly start to rise, although I've never idled long enough for even the 212 (parking lights) fans to come on. In stop and go traffic yesterday, I had the A/C on full blast and it stayed at 180-190 the entire time. Before this, I had a dying thermostat and I was probably seeing 230+ . However, I disagree with the stock gauge not moving deal. Although there is a general "middle range", the gauge does move between 180-230, only it just moves over maybe a 5 degree sweep, you have to look very carefully. Comparing to my VDO gauge, at 180, its at the "bottom" of the "middle", and when I saw 200 recently, it had noticeably moved towards the "middle" of the "middle". I don't know if maybe older gauges just tend to stick until the voltage really pushes them around. I recommend the Fluidyne though, and check to make sure your fans are working. The fans should turn on at 221F, and if your radiator is working properly, that should be plenty to cool off the engine.