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ghsti: Don't understand-what is the problem? Mine always operates just a hair above that line that yours points at.
 

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ghsti: Don't understand-what is the problem? Mine always operates just a hair above that line that yours points at.
the needle points to the normal temp which is above that line, it will be at that point and then once i step on it to pass someone and then let off, i look at the gauge and it sits the mark in the pic. the heater gets colder too.

i have owned this car for 3 years now, i have done the coolant flush multiple times and it never fluctuated.
my AP displays lowest 168 deg F to highest 207 deg F.

so my question is there someone who found a solution to this issue.
 

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the needle points to the normal temp which is above that line, it will be at that point and then once i step on it to pass someone and then let off, i look at the gauge and it sits the mark in the pic. the heater gets colder too.

i have owned this car for 3 years now, i have done the coolant flush multiple times and it never fluctuated.
my AP displays lowest 168 deg F to highest 207 deg F.

so my question is there someone who found a solution to this issue.
Hey I've been having this same thing on my 04 for a long time. I believe it's normal. I would monitor via AP3, and whenever I decrease load downhill my readout would be as low as 174F. Then it would gradually go back up. I just figured the coolant is circulating and cooling everything down while there is no combustion occurring. I'm hardly running my car hard these days because I work and my travels consist of plenty of traffic to and from work. My Mishimoto rad seems to be holding up well for it on a 50/50 mixture of Subaru Blue. No air or anything. If there was air it would be obvious of a brief overheat, and my heater blasts constantly this month with no cold air in between.

On the contrary, I do have a mild concern if anyone would answer, I haven't gotten a clear answer to this. It is cold right now in SoCal, and my cruise to work is about 47-50F ambient. Going about 80mph, is 194-196F normal coolant temp in this considered cooler weather? I don't blast my AC obviously, don't really need use for the fans on the constant drive. Car is remote tuned by IAPerformance. The tuner tuned the car for hot weather back in October because it was as high as 108F ambient at the time, so he was able to make my fans kick in at exactly 200F. But I'm concerned that light load/cruising at 3250RPM, that 194-196F variable is normal? Thanks in advance.
 

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the needle points to the normal temp which is above that line, it will be at that point and then once i step on it to pass someone and then let off, i look at the gauge and it sits the mark in the pic. the heater gets colder too.

i have owned this car for 3 years now, i have done the coolant flush multiple times and it never fluctuated.
my AP displays lowest 168 deg F to highest 207 deg F.

so my question is there someone who found a solution to this issue.
im having this same issue brand new build..
 

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Hey I've been having this same thing on my 04 for a long time. I believe it's normal. I would monitor via AP3, and whenever I decrease load downhill my readout would be as low as 174F. Then it would gradually go back up. I just figured the coolant is circulating and cooling everything down while there is no combustion occurring. I'm hardly running my car hard these days because I work and my travels consist of plenty of traffic to and from work. My Mishimoto rad seems to be holding up well for it on a 50/50 mixture of Subaru Blue. No air or anything. If there was air it would be obvious of a brief overheat, and my heater blasts constantly this month with no cold air in between.

On the contrary, I do have a mild concern if anyone would answer, I haven't gotten a clear answer to this. It is cold right now in SoCal, and my cruise to work is about 47-50F ambient. Going about 80mph, is 194-196F normal coolant temp in this considered cooler weather? I don't blast my AC obviously, don't really need use for the fans on the constant drive. Car is remote tuned by IAPerformance. The tuner tuned the car for hot weather back in October because it was as high as 108F ambient at the time, so he was able to make my fans kick in at exactly 200F. But I'm concerned that light load/cruising at 3250RPM, that 194-196F variable is normal? Thanks in advance.

i have this same issue brand new build 2014 sti, 5858 rotated setup, did it when it was stock and currently still does it. After i shift at 4k til 6th gear and cruise it drops to 174 constantly. city driving its fine or just cruising
 

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Temps will bounce around between 185-207 or so depending on outside weather, and engine loading/engine speed.

Cruising down the highway when its 100degreesF may yeild 200 degree coolant temps.
Cruising down the highway when its 30dgegreesF may yeild 175-180 degree coolant temps.

If you are cruising downhill, off throttle, in cold weather, the coolant temp will slowly decrease a little, but not enough to cause concern.

These should be relativly stable. If you are traveling in town with stop/go traffic temps will fluctuate a bit there as well.

If you see very quick fluctuations in temperature, you probably have air in the system. When an air pocket goes by the sensor, it will temporarily read much higher, then drop back down when the coolant hits it.

If you see moderately quick fluctuations in temperature (temps rising or falling more than a degree per minute or so) then you likely need a new thermostat. The temperature on the AP is measured in the block not the radiator. So, if the temperature is climbing too quickly, the thermostat is not opening to cycle through the radiator. If the temperature is falling too quickly, the thermostat is not closing down to limit cycling through the radiator.

The radiator itself should only become an issue when it is limiting cooling capacity. Such as on a track day. If the thermostat is failed closed, it will simulate this because the coolant circulating in the block is increasing in temperature.

Lastly, stick with ONLY the OEM thermostat. No aftermarket, no "lower temp", OEM or bust. "Lower temp" thermostats do not increase cooling capacity they simply open sooner. Cooling capacity is dictated by the radiator, not the thermostat.

EDIT: the fans on the back of the radiator/condenser should only be of concern while sitting still. If you are moving more than 5-10mph, they shouldn't be needed. I don't know if they actually come on while driving at all though, I would imagine they default to off while in motion, but i could be wrong here.
 

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Is this a problem?

If your coolant temp never varied, the gauge would have no use!
 

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Is this a problem?

If your coolant temp never varied, the gauge would have no use!
Once the car's up to temp... it shouldn't move. It has a huge dead zone built into it -- from 185-215 degrees the stock gauge won't move. This I have personally tested. I assume this was done as this is the normal operating range with the gauge existing only to show when it is outside that range.

Once your temps hit 216 it will become quite sensitive. I haven't tested how much it moves if you drop below 185 though after reaching operating temp.
 

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Once the car's up to temp... it shouldn't move. It has a huge dead zone built into it -- from 185-215 degrees the stock gauge won't move. This I have personally tested. I assume this was done as this is the normal operating range with the gauge existing only to show when it is outside that range.

Once your temps hit 216 it will become quite sensitive. I haven't tested how much it moves if you drop below 185 though after reaching operating temp.
because your average consumer doesn't understand cars, and doesn't want to see a fluctuating gauge. Automotive designers did this on purpose to keep people from worrying about it...

I would be more bothered that I have a wildly inaccurate gauge, but I have an AP to watch live numbers, and I like the numbers ;)
 

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Once the car's up to temp... it shouldn't move. It has a huge dead zone built into it -- from 185-215 degrees the stock gauge won't move. This I have personally tested. I assume this was done as this is the normal operating range with the gauge existing only to show when it is outside that range.

Once your temps hit 216 it will become quite sensitive. I haven't tested how much it moves if you drop below 185 though after reaching operating temp.

because your average consumer doesn't understand cars, and doesn't want to see a fluctuating gauge. Automotive designers did this on purpose to keep people from worrying about it...
Uh, so SOA designed a gauge as only as good as a light? Whatever . . .

I would be more bothered that I have a wildly inaccurate gauge, but I have an AP to watch live numbers, and I like the numbers ;)
Dont remember reading of anything wildly fluctuating here, but you can be sure that a coolant temperature gauge that fluctuates wildly is malfunctioning one way or another, because coolant temps cant heat and cool in a wildly fluctuating manner. That requires energy gain and loss, and that requires time.

So if aren't experience an overheating condition where there is no coolant at the sensor a little movement is no big deal - and to be expected when you get on it, speed up or slow down or run air. Neither your thermostat, or your coolant system are perfect, and the conditions the operate in are always varying.
 

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Uh, so SOA designed a gauge as only as good as a light? Whatever . . .
I was exaggerating a bit, but I never said it didn't have a use. It's use is to tell you that you are inside or outside of the "normal" operating temperatures. It does not, however, give you a more granular level of detail such as actual temperature which is read from the AP. That is all I meant.

Dont remember reading of anything wildly fluctuating here, but you can be sure that a coolant temperature gauge that fluctuates wildly is malfunctioning one way or another, because coolant temps cant heat and cool in a wildly fluctuating manner. That requires energy gain and loss, and that requires time.
Again, I was exaggerating a bit, but that quote has to do with gauge accuracy not temperature fluctuation. A 30-degree dead band is not something I would call "accurate" however I understand its purpose, and it does that just fine.

So if aren't experience an overheating condition where there is no coolant at the sensor a little movement is no big deal - and to be expected when you get on it, speed up or slow down or run air. Neither your thermostat, or your coolant system are perfect, and the conditions the operate in are always varying.
Agree.
 

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Once the car's up to temp... it shouldn't move. It has a huge dead zone built into it -- from 185-215 degrees the stock gauge won't move.
Uh, so SOA designed a gauge as only as good as a light?
I was exaggerating a bit, but I never said it didn't have a use. It's use is to tell you that you are inside or outside of the "normal" operating temperatures. .
No, I did, and you explained that I was correct in calling it only as good as a light very well!
 

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Uh, so SOA designed a gauge as only as good as a light? Whatever . . .

No... they designed a gauge that's good for telling if the car is operating normally or not.

When my thermostat started going out this summer, I would watch the AP as well as the stock temp gauge *very* closely. Any temperature between 185-215 would read at the exact same normal point on the temp gauge.

As soon as the car hit 215, the needle would start to rise. At that point, a degree or two would be enough to make for significant movement. I never got it as hot as the 2nd tick so I'm not sure what temperature that represents.

It makes sense really... the gauge helps you know when the car is warming up and how close it is to being fully at operating temp. Then as long as the gauge stays still, you know the car is operating within normal range. If the gauge starts moving up above that... it's getting hot. Maybe not overheating... but it's getting hot.

Now I personally, like many others here, would prefer it was more linear and exact throughout the range... but I can definitely understand why they made it that way.
 

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yeah - to make a valuable tool exactly like . . . yesss . . . exactly what they are called . . . idiot lights!!

I DD drive an 05 and I never noticed my gauge was so poor. I does move though it doesn't have numbers in it . . . . Yes I have an AP permanently mounted to know , and I use it for warm up every cold start.
 

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yeah - to make a valuable tool exactly like . . . yesss . . . exactly what they are called . . . idiot lights!!

I DD drive an 05 and I never noticed my gauge was so poor. I does move though it doesn't have numbers in it . . . . Yes I have an AP permanently mounted to know , and I use it for warm up every cold start.
I keep going back and forth myself on an actual water temp gauge.

I like knowing exactly where temps are at myself. In the end I keep coming back to that it does do it's job and let me know if it's getting hot... even though it doesn't do so as precisely as I'd like.
 

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I agree It does its job. Mine moves small amounts all the time. There are no numbers to for me to complain about. Still, it could have had numbers for for the same cost.

Old fashioned meter design like yours and mine: The movement has a coil that is driven to full scale by a small current measured in mili-amps. Most often a shunt resistor is placed across it. The variable resistance sensor is connected. But thermistor sensors often used to measure temperature do not normally respond linearly, and often the dial is marked in a non-linear manner. More resistors can be added to the circuit to flatten the curve too. What I am saying is that the response of an old analog gauge will often not be linear and engineers work to make them more linear, not the other way round. Regardless of linearity, the gauge can be marked with numbers appropriately.

New cars use the same sensors, but are a while different ball game after that. The in circuit values, whatever they are, are measured accurately and can be compensated very well in code . . . Still linearization of the circuit is often done to maintain a minimum of resolution.
 

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On my old 2005 STi bone stock, CSF Radiator, with 166k miles the car would cruise around 180-185f on a normal day. It would slowly creep to 204f when the coolant fans would kick in and bring the temps back down to 190f before turning off again. If the motor was heatsoaked in traffic, the coolant temps would slowly creep back up from 190f to 204f triggering the cooling fans as necessary. Once airflow was gained, the temps would settle around 180-185f again.

I monitor the temps using a bluetooth OBD2 adapter and the Torque Android app. Its much more accurate than trying to see if the needle moved 1mm. (Yes you can read the needle movement but its almost invisible and soo hard to establish a baseline unless you carefully sit upright in the same seating position each time when you stare at the temp needle to see if it moved 1mm.)

My "new" 2005 STi the car has a fresh built longblock and misimoto rad cruises around 174f. Everything about this engine seems to be 10 degrees cooler in operation than my old STi. It still climbs to 204f in traffic which triggers the cooling fan but it seems, in general, the engine runs 10 degrees cooler than my old car. I think its because the coolant channels and cylinder jackets are clean and haven't been contaminated with corrosion buildup and oily residue from having previously blown a headgasket so the coolant can more efficiently pull away heat from the metal walls.

 
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