28 replies to this topic

[Randy Wolfgram]

First timer here, so still trying to figure out what is normal for this car.  I bought the car in March and had it up at Thunderhill late in the summer with 100+ ambient temps and the car ran between 210 and 219, in clean air for most of the day, with a couple of blips up around 221 later in the day.  Readings are coming from my data logger with the sensor on the thermostat housing.  CSF radiator (no bent fins or clogs) with a 16 lb cap, no thermostat and the heater core is not bypassed.  Fan works fine, but doesn't come on until around 219, at which point the car cools back down to around 210.  I've read multiple threads on overheating issues, but some are saying these cars should not run much over 190, even in high ambient temps and others are saying it's fine.  Since I'm just getting started, I really want to figure out if I should be chasing this as a problem or not so looking for advice on whether or not I need to worry about this.

 

Thanks in advance.

[James York]

Randy,

 

I would say 220 in clean air is too hot.  I never see above 200 at any ambient temperature in clear air.  You aren't overheating yet, but I would suspect you are losing some power.  (I can't recall the 95 ECU maps)

 

My guess is that the culprit is your radiator.  For maximum cooling, most SM's use multiple pass cross flow radiators.  I think the CSF is a single pass top/bottom tank type radiator.  Not the best you can buy.

[Alberto]

Randy,

 

I'd suggest starting with the thermostat.  Get a 180* tstat.  I also felt my 1.6 power fall off during the race when using the OE thermostat (192*) until I switched to the 180*.  Now my temps stay under 200* F most of the time.  On 100* Thunderhill days, it will creep up but I don't recall it going over 205-210.

 

http://blog.miatarac...spec-miata.html

 

I think the CSF is probably fine.  I run a Koyo but plenty of people locally running CSF, Mizu etc and able to keep temps at bay.

[RWP80000]

Randy,

Based on your observation that the fan doesn't come on to 219 deg. (197 deg is more typical) the first thing I would do is verify the data logger output.  One way would be to remove your sensor from the t-stat housing and put it in ice water and then in boiling water.  Your data logger should display pretty close to 32/212.  You may have the wrong sensor/calibration selected for the data logger.

 

I know many people run w/o a thermostat but I am in the camp of having one (or at least a restricter to simulate the flow limitation of a stat.  I also prefer running a 160 deg stat. 

[Randy Wolfgram]

Okay.  Appreciate all of the input.  I'll start by re-calibrating the sensor.  Lot's of opinions on running a t-stat vs not so can be confusing for a noob.     I can certainly throw one in to test.  I would definitely like to do all I can to eliminate things before I go with a new radiator.  Not sure if it makes a difference or not, but I get the same results just letting the car run in my driveway (heats up to 219, fan kicks in and cools back down to 210, rinse and repeat) as I do under load on the track.

[Dennis]

The Mazda spec for the fan is 207*. I have had 2 different digital temp gauges with the sensor in the hose that goes to the heater core from the back of the head. These gauges read 219-220 when the fan comes on. I have replaced both Mazda sensors that talk to the computer and got the same result. I use this information to "calibrate" my gauge, since it isn't measuring coolant temp in the same place as the computer, so I figure my gauge reads about 12* high compared to what the computer is seeing. So when it's 100* at Thunderhill I am in the teens in clean air and in the 220s when drafting and I think that's ok.

Dennis

[Ron Alan]

^^207 stock!

But it would seem you are still running hotter than you should. I'm always at 180-190 with aftermarket sensor in stat housing.

[Randy Wolfgram]

^^207 stock!

But it would seem you are still running hotter than you should. I'm always at 180-190 with aftermarket sensor in stat housing.

 

Okay, another good data point (assume this is on your '95?).  We are sampling at the same place.  So... short of just dropping in a new radiator (and, other than calibrating my sensor), is there anything else that I should try to eliminate or is that the most likely culprit?

[Johnny D]

Assuming your heater works, etc, have you run with the heater fan on ??

Not the culprit but could drop your temp.

J~

[Ron Alan]

Am I remembering at some point early on you had an overheat issue? Regardless...assuming no issue with the water pump a radiator my be in order. I have a new one you are more than welcome to install(borrow)and see if things change. If it does then you'll know the problem! If not...need to keep searching!

BTW...maybe in the summer but this time of the year I can hardly get either of my cars hot enough for the fan to come on when it is just idling!

[Randy Wolfgram]

Assuming your heater works, etc, have you run with the heater fan on ??

Not the culprit but could drop your temp.

J~

 

Ya, I can get it to drop the temps a bit with the heater on.

 

 

Am I remembering at some point early on you had an overheat issue? Regardless...assuming no issue with the water pump a radiator my be in order. I have a new one you are more than welcome to install(borrow)and see if things change. If it does then you'll know the problem! If not...need to keep searching!

BTW...maybe in the summer but this time of the year I can hardly get either of my cars hot enough for the fan to come on when it is just idling!

 

Ya, I think we spoke about it briefly after I got back from Thunderhill, just now getting around to trying to do something about it.  I may take you up on that, Ron.  I can get mine to do this just idling in the driveway.

[Johnny D]

FYI, there's free SCCA Test Day at TH Dec 28th.

J~

[Randy Wolfgram]

FYI, there's free SCCA Test Day at TH Dec 28th.

J~

 

Oh, good to know.  If we end up staying around for the holidays, I know what I'll be doing.

[Garido]

Can I just say I found this thread helpful for my own situation. Initially I had issues with overheating which I determined to be a faulty sensor but even after correcting it, I still wasn't satisfied with temperatures for my car. A lot of the information was quite useful so thanks to all. I hope these threads are archived to help others in the future.

 

~ Garido

[Randy Wolfgram]

Can I just say I found this thread helpful for my own situation. Initially I had issues with overheating which I determined to be a faulty sensor but even after correcting it, I still wasn't satisfied with temperatures for my car. A lot of the information was quite useful so thanks to all. I hope these threads are archived to help others in the future.

 

~ Garido

 

What ultimately solved your issue, Garido?  (or, are you still chasing as well?)

[Alberto]

Ron, I'm guessing by your temps that are not running a thermostat.  Right?

 

I tested the 160* thermostat and no tstat.  Couldn't get the car up past ~185* measured at the back of the head with the 160*.  In colder weather (like now in SF Bay) I couldn't get the car sufficiently up to temp on track with the 160* or when not running a tstat.  I'm running the big Koyo rad.

[Garido]

What ultimately solved your issue, Garido?  (or, are you still chasing as well?)

 

Hello Randy,

I had issues with the radiator where the heat dissipation wasn't consistent. I regret buying some parts second hand, a radiator being one of them. Despite doing what I feel was an adequate flush, I may have dislodged some debris further in the radiator. I believe this could have been the cause for my issue. Using a thermometer I was able to find cold and hot spots on the radiator however over the course of time, the spots would change.

 

This was the only conclusion I could come to.

[Ron Alan]

Ron, I'm guessing by your temps that are not running a thermostat.  Right?

 

I tested the 160* thermostat and no tstat.  Couldn't get the car up past ~185* measured at the back of the head with the 160*.  In colder weather (like now in SF Bay) I couldn't get the car sufficiently up to temp on track with the 160* or when not running a tstat.  I'm running the big Koyo rad.

Good question The car hasnt been apart in 3 years...I hardly remember what i did 3 days ago! But if i had to guess it is a 180 stat...as I believe this is what Mike would but in this car. He is not a no thermostat guy.

 

Quick question for someone in the know. I bought a street 99 that came with a bunch of maintenance items in a box...oil, belts, filters and a thermostat. The thermostat is not a Mazda(Fram i think)but I'm sure the previous owner went in and asked for this stuff...didnt grab it off a shelf. The thermostat is 192 degress...is that correct?

[Alberto]

yep.  stock should be. 

 

see if there is any stamping on the brass.  i have some pics in the link to my blog above.

[Randy Wolfgram]

Sensor calibrated so the temp readings I have logged are valid.  I've got a Springfield Dyno radiator on the way.  I have a question for my ignorance.  If the ECU is supposed to turn the fan at around 207*, what are the factors that would contribute to it coming on at around 219*?  Faulty coolant sensor?