Water temp in AEM EMS

[menfou]

Hello,

On my stock water gauge, my water temp is normal(less than middle), but in the AEM EMS the water temp is ~90°C, and if I accelerate at full throttle the water temp is 125°C on the AEM EMS, but always normal on the gauge.

After 30minutes on track, I can see "blo blo blo blo blo" in the engine , I think the water boil; but on the gauge I have less than the middle

On stock engine, with just exhaust header and AEM EMS
Datalog

 

[m3456y]

Hello,

On my stock water gauge, my water temp is normal(less than middle), but in the AEM EMS the water temp is ~90°C, and if I accelerate at full throttle the water temp is 125°C on the AEM EMS, but always normal on the gauge.

After 30minutes on track, I can see "blo blo blo blo blo" in the engine , I think the water boil; but on the gauge I have less than the middle

On stock engine, with just exhaust header and AEM EMS
Datalog

I had the same problem. The AEM water temperature calibration on mine was wrong when I installed it. Go to aempower.com look in the forum and you'll see it's a common problem. You need to change the calibration values.

 

[greenberet]

menfou, what program should the datalog be opened with?

m3456y, so after calibration your AEM doesn't show a rising a coolant temperature when you floor it and it did before you calibrated it? The coolant temperature now stays as stable according to the AEM as is does according to the stock gauge?

 

[m3456y]

menfou, what program should the datalog be opened with?

m3456y, so after calibration your AEM doesn't show a rising a coolant temperature when you floor it and it did before you calibrated it? The coolant temperature now stays as stable according to the AEM as is does according to the stock gauge?

Mine stays pretty constant now. Around 197-205 degrees here in Florida. I have type R hood and duct as well.

 

[greenberet]

That's good to know. If the coolant temperature increased when you were driving hard yet the stock gauge didn't show it, I'd get nervous the next time I was on the Autobahn.

 

[Daedalus]

You guys shouldn't be comparing the stock gauge to the AEM readings. They don't even use the same temp sensors. The stock gauge is pretty numb by design, barely any better than the oil pressure idiot lamp. The ECU sensor is higher quality (more accurate) and has a much wider range--the resistance change for a given change in temp is several times that of the gauge sender. When you calibrate it use the data from 11-48 in the '91 FSM. I would also check the accuracy of the sensor first per the instructions on the same page so you know it's correct to begin with.

 

[nsxotic911]

You guys shouldn't be comparing the stock gauge to the AEM readings. They don't even use the same temp sensors. The stock gauge is pretty numb by design, barely any better than the oil pressure idiot lamp. The ECU sensor is higher quality (more accurate) and has a much wider range--the resistance change for a given change in temp is several times that of the gauge sender. When you calibrate it use the data from 11-48 in the '91 FSM. I would also check the accuracy of the sensor first per the instructions on the same page so you know it's correct to begin with.

Does that mean that when my bar is at halfway.. it is actually wrong and I could be overheating?

 

[Daedalus]

Does that mean that when my bar is at halfway.. it is actually wrong and I could be overheating?

I'm saying it's not a good idea to try to make meaningful correlations between the dash gauge and the actual coolant temp. A 10*F temp difference can make a feelable difference to the fuel and timing maps, but it may be unnoticeable on the gauge. If the gauge is in the red, and assuming it's working right, then you are operating outside the safe temp range and you are at risk of damaging the engine. But the gauge reading "normal" doesn't mean too much if you're looking for incremental gains on the track, just like having the oil pressure light off doesn't mean too much either. If the ECU has any measure of safety it will try to prevent overheating--and thus reduce performance--before the gauge says you're overheating.

If you are really curious (if you have an AEM without FI you probably are) then you need to manually measure the sender's temp-resistance relationship, since the FSM only gives 2 points of reference (perhaps indicating its relative lack of importance). Then look at the gauge's position-resistance relationship using a multimeter and variable resistor. You can only characterize the sender to 212*F using water, or higher with a different fluid (glycol?) or a pressure vessel, but 212 may be good enough to extrapolate out into dangerous temps (or maybe not, depending on how flat the curve becomes). Use the same methods you use to verify the accuracy of the ECU's temp sender. Test all 3 and you will have painted a fuzzy picture of about what temp the coolant under the throttle body is for any position of the gauge needle.

 

[greenberet]

Looking at the service manual, the sensor that tells the ECU how warm the water is measures the temperature of the coolant coming out of the engine. The separate sensor that drives the water temperature gauge in the cockpit also measures the temperature of the coolant coming out of the engine. At "high coolant temperatures" the ECU retards ignition timing, reducing horsepower, and at coolant temperatures above 130°C the air conditioning system shuts down. Unless something is broken, I'd hope that the gauge in the cockpit shows that the engine is getting uncomfortably hot if it actually is.

Menfou's AEM showed water temperatures between 90°C and 125°C while the stock gauge just sat at its normal position. Has anyone else seen such a variation while the stock gauge didn't register any temperature change? Does anyone have experience at what coolant temperatures the stock gauge starts showing an above-normal temperature? My stock water temperature gauge doesn't show any temperature increase at all during top speed runs but maybe the coolant is actually getting hot enough that the ECU is pulling ignition timing. It would really suck if the engine were getting close to overheating but the stock gauge didn't let you know.

 

[nsxotic911]

Looking at the service manual, the sensor that tells the ECU how warm the water is measures the temperature of the coolant coming out of the engine. The separate sensor that drives the water temperature gauge in the cockpit also measures the temperature of the coolant coming out of the engine. At "high coolant temperatures" the ECU retards ignition timing, reducing horsepower, and at coolant temperatures above 130°C the air conditioning system shuts down. Unless something is broken, I'd hope that the gauge in the cockpit shows that the engine is getting uncomfortably hot if it actually is.

Menfou's AEM showed water temperatures between 90°C and 125°C while the stock gauge just sat at its normal position. Has anyone else seen such a variation while the stock gauge didn't register any temperature change? Does anyone have experience at what coolant temperatures the stock gauge starts showing an above-normal temperature? My stock water temperature gauge doesn't show any temperature increase at all during top speed runs but maybe the coolant is actually getting hot enough that the ECU is pulling ignition timing. It would really suck if the engine were getting close to overheating but the stock gauge didn't let you know.

I recently did a coolant flush and monitored things closely while I got all the air bubbles out.. .. I was watching both the AEM reading, and the stock gauge at idle.

From about 180-20xsh, the stock gauge showed at mid or a hair under.
At 210sh to about 220 (afterwhich I shutdown to inspect) the stock gauge went up slightly one bar.
In my experience, this seems fairly reasonable. This has at least been my experience.

If you're hitting 260 on AEM and not on the stock gauge, then that is a problem, me thinks.

With that said, I concur with others on this forum; o not trust the stock gauges if you are driving the car hard else it only needs to be wrong once before things blow-up.

 

[jorligan]

Just got back from a 2100 mile road trip with Turbo NSX using AEM. Water temp peaked at 205 on AEM while sitting in rush hour traffic in NYC (right next to solid municipal waste tanker - right, smelled like sh-t) for 45 minutes, no change on the stock temp gauge, 1/2 way. Driving on the highway, 158 on AEM and still, temp gauge 1/2 way.