Temperature gauge operation question

[RABID_MP5]

My daughter's 2010 Mazdaspeed3 (yeah color me envious) has no temp gauge, just a red "hot" light. (I heard they added a blue "cold" light in 2011?)

Major frowner. But anyway, when I looked into this people were also faulting basically all cars in the post mid-90s OBD2 era. Basically the claim is that the water temp sensor is hooked to the computer, but that it does not really echo the same temp values to the gauge, especially above normal operating temp. It just suddenly rockets when the ECU decides "too hot!".

We all know the P5 gauge indeed rises with warm-up. But when I thought about it, in 5 years I've never seen my gauge even creep up above normal, even idling in July at a stop light. I do recall back in the 80s that yeah you could see the temp gauge actually rise and fall a bit as the electric fan cycled.

Anyone else weigh in on this?

 

[tweety2300]

The one in my mp3 moves a little bit. 323 is never in the same spot when I look at it. I honestly hate not having a temp gauge.

 

[pcb]

I just got an Ultra-Gauge mostly for that specific reason. When the temperature gauge on the car finally does move, it may well be too late. The Ultra-Gauge does show the temperature fluctuating but I haven't let it idle till the fans come on yet (I just got it). I will set the adjustable alarm to go off just after the point when the fans come on. I was worried that I wouldn't even notice the cars gauge moving because it has never moved above half way so I'm not used to checking it. I don't think there is an accompanying MIL light either. (I've got an MP5)

 

[tweety2300]

Nope no light comes on, gauge just goes up

 

[Installshield 2]

As mentioned, the stock gauge is more of aesthetics then anything useful...at least on proteges...so in the case of your daughter's MS3...its mostly the same, functionally...

personally...the only one that i find very useful is oil temperature, anyway...while an accurate and 'real time' reading of water/coolant temp can be useful for understanding radiator efficiency and stuff like that...its very limited for a few reasons:

the sensors ability to read data is only possible when two variables are met...

A) coolant is actually in there...

B) coolant is actually circulating...

if one of those things gets messed up, the reading won't budge (or even in some cases, it'll actually fall)...so as a driver you can be under the impression that everything is fine, when in reality your water pump just took a dump and splattered coolant all over the road...continue on, engine is toast...etc...

oil though...that has its face in it the whole time...and seeing fluctuations in oil temp is much more useful from a maintenance stand point...and in most cases oil temp will start rising dangerously BEFORE the circulating water is heat soaked...so you'll nearly immediately know something is wrong and get the engine off...

 

[tweety2300]

As mentioned, the stock gauge is more of aesthetics then anything useful...at least on proteges...so in the case of your daughter's MS3...its mostly the same, functionally...

personally...the only one that i find very useful is oil temperature, anyway...while an accurate and 'real time' reading of water/coolant temp can be useful for understanding radiator efficiency and stuff like that...its very limited for a few reasons:

the sensors ability to read data is only possible when two variables are met...

A) coolant is actually in there...

B) coolant is actually circulating...

if one of those things gets messed up, the reading won't budge (or even in some cases, it'll actually fall)...so as a driver you can be under the impression that everything is fine, when in reality your water pump just took a dump and splattered coolant all over the road...continue on, engine is toast...etc...

oil though...that has its face in it the whole time...and seeing fluctuations in oil temp is much more useful from a maintenance stand point...and in most cases oil temp will start rising dangerously BEFORE the circulating water is heat soaked...so you'll nearly immediately know something is wrong and get the engine off...

Good to know, I was actually about to get a oil pressure and water temp gauge, guess I should get oil temp instead?

 

[Installshield 2]

^^its your call man, but i was having the exact same debate a few months ago...and got a oil pressure and oil temp gauge for the above reasons...

not plugging or anything...but check out www.speedhut.com...great prices, and they'll do all kinds of custom stuff for cheap...I haven't installed mine yet, but i'm happy with them...

the sending units and wiring are all high quality too, with extension looms and stuff so that you only need to find one power source, one illumination switch, etc...despite multiple gauges...

 

[i12drivemyMP5]

My daughter's scion xb had that s***. Stupid, hated it. 2 idiot lights for the same function. Twice as idiotic. I know the ****** water is cold until the motor heats up. Why not do the same retard s*** with the oil pressure light? Make it green when enough pressure and red when not enough. Like you don't know s*** is OK when the red light isn't on. I'm sure there are plenty of stupid ***** that'll freak out over the blue one but ignore the red one that actually matters. I think the P5 one will lower barely when the fan runs but I don't stay sitting still long enough to notice. I have to stop and sit for a minute or 2 before the fan will start cycling(without AC on) even after driving 30 miles to work.

 

[tweety2300]

Same reason people get in their cars and drive not giving it 2 seconds to warm up in 20 degree weather. I guess the blue light is to try to get people to stop doing that and to actually let it warm up

 

[Spiced MSP]

My temp gauge works just fine. At operating temp, it sits right in the middle, whether it's 40* outside or 105*. I have had my fair share of coolant issues with my car and every time, I noticed my temp gauge started to rise slowly above the normal temp on the gauge. So, I would blast the heat to lower the temp in stop and go traffic and/or speed up to increase the flow of air through the radiator along with increase of the flow of coolant since the water pump is dependent on the engine speed. I have had my temp rise significantly several times and my gauge reflected that pretty well. But, I never let it peg the "H". But those issues were due to me messing around with it after swapping to a different radiator setup. With a properly maintained cooling system, you shouldn't have to worry about anything. The gauge works as intended throughout the entire temp range. If you don't have any coolant leaks, have a good working radiator cap, thermostat and water pump, the temp will never rise. If you don't open up the system a lot and the coolant is always topped off, the temp will never rise. If there are no air pockets in the system, the temp will never rise. You shouldn't be surprised if you go extended periods of time with your temp gauge sitting right in the middle. That's where it is supposed to be. Im pretty sure you may throw a code when the temp sensor starts acting up. So pretty much, as long as you have no leaks and coolant stays topped off along with the overflow, you have nothing to worry about

 

[Spiced MSP]

also, it isn't required to let your car warm up when cold. That's what the fuel and timing maps are for. Letting your car warm up is doing nothing but wasting gas. I mean of course, you let it warm up to heat up the interior for a comfortable drive. But just to warm up the engine is pointless. The ECU adjusts fuel and timing for this reason and as the car warms up, the fuel and timing is adjusted even more until the car reaches operating temp. There is a reason there is open loop and closed loop operation. You notice on a cold start, the car idles high. The ECU opens the IAC to a certain point while injecting more fuel since fuel doesn't atomize well when it's cold. As the temp warms up, the IAC adjusts some and the fuel is adjusted, bringing the idle down. If you drive off right after a cold start, you will notice the idle will still be high when you come to a stop, in between shifts or coasting in neutral. There is nothing wrong with driving after a cold start. Everyone still does that even though they drive a modern car with fuel injection and a ECU and not a carburetor. This reminds of how some people swear by getting gas early in the morning because it's cooler and you get more gas as a result. SMDH

OAN: On cars with forced induction, you can still drive after a cold start. However, it isn't recommended to start boosting since the car will be operating off of preset parameters and not the sensors themselves.

 

[pcb]

I hooked up my Ultra-Gauge and idled my car in the driveway to see how the factory and UG compare to each other. They both followed each other until the temperature hit 71*C then the factory gauge hit the "just below middle" mark where it went sleep. The UG showed the temperature rising steadily to 88*C where it stayed for quite a while as the thermostat opened up. The temperature then rose steadily to 97*C when the fans kicked in bringing the temperature down to 90*C where the fans shut off. The temperature cycled between 90*C and 97*C three times before I shut the car off.
I believe the factory gauge should show all that movement between middle and H because I am not in the habit of even looking at it because it is always sleeping. I would rather have an idiot light than this stupid factory gauge. At least I would be made aware of a hot situation the instant it happened instead of hoping to notice the gauge moving. I have never seen the gauge move above it's just below middle mark in the 3 1/2 years I've had the car. I suppose I could disconnect the fans to see how friggen hot it has to get to see some movement on the factory gauge but I'm hesitant to do that.
If my fuel gauge only went to half and stayed there until the fuel low light went off, I'd disconnect it and use my trip meter.
I had an 85 626 and the heater core hose blew off on the highway and I didn't notice the temperature gauge until it was too late, warped my head. All of that could have happened in less than a couple of minutes. Perhaps like Installshield 2 said, there was no fluid on the sensor but the gauge did read hot. (when I finally noticed it)

OAN: I doubt that getting gas early in the morning would make any real difference. All the gas (except maybe the bit in the pump itself) comes from the underground tank which is a pretty consistent temperature. Our pumps here are temperature adjusted to 15*C so if you were to fill up a few 40 gallon drums when it's -20 outside you might might see some savings but I don't think that's worth the effort.

 

[pcb]

the sensors ability to read data is only possible when two variables are met...

A) coolant is actually in there...

B) coolant is actually circulating...

Is there such thing as a coolant pressure switch (or maybe flow switch) ?? It seems like that might cover those two issues.