My temp gauge always reads low. It does rise to just below the low line when I turn the car on, and after warming up, it reads just above the line. I don't know if the car still has its thermostat, if not, that would contribute. Any ideas on what I should check?

 

you can always check the thermostat sensor's output. Most "modded" cars run an aftermarket temp gague as well.

LOL - my 929 never reads above 25% except on cool humid nights.

 

Where is the sensor located? I just checked the factory service manual and don't see it.

 

The gauge is moving so it's probably OK. So if says the engine's running cold, it probably is! Your thermostat may be stuck open. Replace it with a Mazda one.

 

If the thermostat is stuck open, I'll leave it as is. If its missing, even better. Colder thermostats result in better power, so no thermostat (coldest possible) is what I'd want to do any way. Just concerned because once I'm done witht he suspension, I'll be trading the stock fan for an electric, and want evertying working right. Thanks though.

p.s. I've looked around under the hood, and in the manual, and I still don't see the temp sensor. Hint, please?

 

Their are a couple of these cooling senders.

-Water Temp Switch- Bottom lrft Rad. Sends cooling status directly to ECU. Used duing start up when Hi rpm's are Involved.
-Coolant Level Sensor- Top of Rad. As name Implies, keeps check on your level of coolant.
-Water Temp Sensor- Directly relayed to ECU. ECU than adjusts necc. components. TPS, ACV etc.
-Coolant Sender Unit- Located below Oil Filter on top of left engine mount. Sends temp to the Instrument Cluster so, you the driver, know the engine temp status.

I have replaced all these sensors to assure that I am never left with a cooked motor which won't take long under extremely hot conditions.

 

My temp gauge has never read above the half way mark of the stock gauge on my 86RX7. I was considering removing thermostat eliminating the fear of a stuck closed condition. I live in St. Louis Mo and its hot and humid 90's during the summer. My car is only driven less than 3k a year so its just a toy. It has 135K on it. Had it since odometer had 23 miles on it.

You can check gauge without having to run engine to temp to see if gauge does full sweep.

 

How do check the gauge without warming up the engine? It doesn't move until the engine heats up a bit.

 

Just get an aftermarket guage, Mazda's suck *** engineers made it a 3 postition sensor. It move to "H" at 250*F....

I've had my temp fluctuate between 170-200 and the stock guage just stay in the same spot... as ALWAYS.

 

Yikes! 250F? Are you sure? That's a crispy motor, isn't it?

ps What should I look for in a gauge? ie How do I tell quality by looking at a catalogue?

 

Wrong, wrong, wrong...
Go and read this thread.
The power gain from running at a lower temp would be minimal. If you want to do this it should be done using a thermostat with a lower opening temp. The engine will run far too cool without one, reducing power and economy because of rich mixtures, and increasing wear.

 

OK, I'll buy the not warming up quick enough, and maybe even the not warming up enough points, but physics dictates that cooling capacity is not impared by lower coolant temp and or velocity. So I'll make sure to have a working 160F (or warmer if I don't find 160F) thermostat in there.

Now, as for after market gauges: What should I look for in a gauge? ie How do I tell quality by looking at a catalogue?

 

Your physics has some holes...
Heat transfer is not an instantaneous process. The longer two objects are in contact, the closer they will get to having equal temps. So the faster you flow coolant through an engine, the less heat it will absorb. The coolant may be being cooled by the radiator, but the engine isn’t being cooled by the coolant. Obviously, if the flow is too slow, the cooling system will not be able to remove heat as fast as it’s being generated. This means there is an ideal coolant flow rate for maximum heat transfer. The cooling system is designed with this in mind, and removing a significant restriction to the coolant flow will change this.
A 160ºF thermostat is better, but I still think that’s way too cool. Why do you want to run such low temps?

 

hmmm...I never though about cooling like that. Good info NZ!

 

"So the faster you flow coolant through an engine, the less heat it will absorb."

I see where you are coming from, and since this is the panultimate question on all Internal Combustion Engine powered vehical forums, I'll only make a breif (relatively) statement.

While each gram of water spends less time in the engines coolant passage and therfore transfers less heat energy away from the engine, a greater mass of coolant flows through the engine. So while each gram of water caries less heat, there are more grams of water cariying that heat, so it should come out similar or equal as far as cooling capacity is concerned. Without a comprehensive, highly controled test on hundreds of identical engines, this debate will not likely be decided. I appreciate your help though. I had not considered the increased time for warm up, or the factor of too low a temp during everday driveing causing problems, so again, thank you.

After reading other posts, and threads, I think it likely that my gauge is bad, because it has never been more than a fraction above the low temp line, yet I know the engine is producing plenty of heat. So, what gauge do you recomend? Of course, I'll have to test everything according to the FSM this weekend before I make any purchases. Thanks again.

 

What do you think manufacturers do every time the design an engine? They have decided this debate...

 

I would think most of you know this; but i didnt see it brought up. it is possible i missed it though. for what it is worth the temp guages have a divding line. the 86-88 are the same (i know the 87-88 are. not sure about 86 so from here on out ill leave the 86 out..but ithink it would be grouped with the 87-88) and the 89-91 are the same. The original poster never said what year car his was..i dont think. the guages for the 87-88 work a little more accurately to what the temp actually is. the 89-91 is basically a idiot lght in the form of a guage

 

I AM NOT QUALIFIED TO ADVISE ANYONE, ONLY TO MAKE MY OWN DECISION AND JUDGEMENT, AND ACCEPT RESPONSABLITY FOR THE RESULTS, GOOD OR BAD.

That being said, I have already conceaded that running without a thermostat is a bad idea because of the start-up and too cold issues, so the rest of the debate is mute. What every my reasons for initially wanting to run thermostatless, I failed to consider all the variables. With your help, I have rectified that situation. DON'T RUN WITHOUT A THERMOSTAT. I KNOW I INITIALLY STATED THAT I WANTED TOO. I WAS WRONG.

More to my problem. It's an 87 N/A. I apologize for the lack of info. After testing my sensor and gauge per the FSM this weekend, I'll likely be replacing one or both. What factors affect accuracy in a gauge? I like to know why I'm doing what I'm doing. If you can advise me on this more specific subject, please do. Thanks.

 

Whoa man, don’t get so wound up! I’m just sharing some info with you, no insult intended.

The temp gauges don’t usually lose accuracy; they just stop working entirely if something breaks. It’s a lot more likely the engine actually is running cold because of a stuck thermostat. You should pull it and test is as per the FSM, or just replace it.
BTW, what were the results of your tests on the sender and gauge?

 

Obviously my last post was poorly phrased. I did not intend to be defensive. My mannerisms are very firm and to the point. Great for conveying info , terrible for social interaction .I was just trying to get the thread back on target.

I'll let you know how the test come out saturday night.

Thanks again.