I was bored at work today and my stock water temp gauge is always in the middle. I know the gauges are not linear. So i put a thermometer onto the car and watched it as the car warmed up. This is not a kitchen thermometer, its a complete kit to test core coolant temp that my friend has, so its pretty accurate. Under normal conditions the fans come on at 230F. With the parking lights on, it comes on at 215. With the ac on 1 the car stays pretty much at 200. My ac need to be rechared so the ac clutch never comes on, just the fans come on. I check my coolant every few days and once in a while its a little low, maybe a few table spoons or so. When the temps hit 230 the pressure overcomes the ast cap and coolant bubbles out. Not much but a little. With the parking lights on this never happened. Instead of changing to the miata thermoswitch, i think i'll just run the car with the parking lights on and the ac on in traffic. I cant believe mazda designed the cooling system like this.

 

The stock fans come on at 221F and at about 207F with the parking lights on, so your temp setup is reading a bit high. That's just the way Mazda did it. You should be boiling over though, sounds like you need a new radiator cap.

This is a cool feature of the PFC, you can have the fans turn on at lower temps to help keep the car cool. Also, make sure you are running no more than a 25/75 coolant-water mix. Too much coolant-to-water makes the car run hotter.

 

what do the parking light have to do with it? what is the logic behind this?

 

Due to higher electrical loads, the EL unit sends the computer a signal to turn the fans on earlier.

 

230F is right on the money, thats when low speed fans really turn on the workshop manuel states 221F Mazda miss print again.Thats why these cars are so prone too overheat small cooling system, tight engine compartment, fans turn on way too high temp = high failer rate.Instead of driving with youre lights on all the time?wire in a aftermarket adjustable fan controller set at 200F turn on temp, thats 30F lower than stock I think in the long run would make a huge differance for engine life.Bigger radiator, second stock oil cooler, better sealing, new t-stat, ss downpipe also improve cooling greatly.

 

Do the fan mod. I keep my fans on all the time while my car is running, and it keeps the temps down at 180F most of the time. With the fans turned off my temps jump up to 210 during normal conditions. Fan mod- easiest and best mod I have ever done.

 

By the way I read 180 with stock cooling system, in FL, with an autometer electrical temp gauge in the thermostat housing. Results may vary, but 30 degrees drop is pretty good for a 5 min mod that costs about $2 for a switch and a piece of wire.

 

This may explain one reason our Canadian cars overheat less. We have DRLs, so our driving lights are always on. The other reason is ambient temps. which rairly exceed 80 F. However, on a trip to the coast at the end of August, I saw the following - normal operating temp on PFS 88 C. After stopping for gas etc and going again, it climbs to 92-99 C and takes over 5 min to go back down to 88 C. On a -long- (5 km +) 8% grade climb at 100 kph (62 MPH) it peaked out at 116 C. No boiling or anything, but it had me a little worried so I checked the boiling temp of my glycol coolant (4 liters coolant and the rest distilled water) - it is about 130 C.

Next year I install the SR radiator (Kyosho?). It may stabilize it a bit more as it holds more coolant. More coolant can absorb more energy, and should slow down the temp changes. I would expect the same temps on long runs though, as I believe our cars are "coolant air" limited. The only fix for this would be enlarging the air duct through the rad (and a larger rad such as the Kyosho) something like what N-Tech does with his "shark nose" mod. Maybe removing the fog/driving lights would allow a bit more air to get through.

 

My car already has the koyo radiator, i flushed the engine twice, it has a original mazda ast cap and i'm running more water than coolant, about 60% water, i guess. I am sure my car is running as efficient in ever way possible. I rather just leave the parking lights on and use the ac button. I will be getting the pfc in a few months and wont be doing the miata mod. And i basically dont want to do anything else to this car. I just want to drive it.