Coolant Temperature Questions

[bogle]

Here's some tables. All are with 2.2k pullup resistor.

The NSX ECT sensor from infinity tuner:

Ohms table

ohms: F
250000: -9
21267: -4
9533: 14
6600: 25
4840: 36
3667: 46
2829: 57
2200: 68
1711: 79
1320: 90
1000: 104
733: 122
508: 149
314: 181
147: 226
0: 263

Voltage table


V: F
0: 263
0.16: 244.1
0.31: 226.37
0.47: 203.33
0.62: 181.65
0.78: 165.13
0.94: 148.82
1.09: 135.83
1.25: 121.98
1.4: 113.35
1.56: 104.14
1.72: 96.94
1.87: 90.22
2.03: 84.54
2.18: 79.26
2.34: 73.63
2.5: 68
2.65: 62.72
2.81: 57.09
2.96: 51.81
3.12: 46.18
3.28: 41.04
3.43: 36.24
3.59: 30.63
3.74: 25.35
3.9: 19.72
4.06: 14.09
4.21: 8.34
4.37: 2.19
4.52: -3.57
4.68: -5.75
4.84: -7.63
4.99: -9

Here's @Old Guy's ohms table above mapped onto the AEM volts scale. Looks like it might read a little low at operating temp? Edit: it jives more with the s2k one posted above than the infinity scale above.....

V: F
0: 263
0.16: 253.28
0.31: 227.26
0.47: 190
0.62: 167.71
0.78: 153.22
0.94: 139.2
1.09: 130.72
1.25: 121.67
1.4: 113.19
1.56: 104.14
1.72: 99.05
1.87: 94.34
2.03: 89.31
2.18: 84.6
2.34: 79.57
2.5: 74.55
2.65: 69.83
2.81: 64.15
2.96: 58.47
3.12: 52.4
3.28: 46.34
3.43: 40.66
3.59: 34.6
3.74: 27.57
3.9: 18.88
4.06: 10.18
4.21: 2.03
4.37: -4
4.52: -4
4.68: -4
4.84: -4
4.99: -4

EDIT2: And here is what came in my car (AEM series 1). Seems mine is even lower for a given voltage reading than Old Guy's. For a while I had an AEM coolant temp gauge sensor at the radiator as well, and they would basically agree. The car hovers around 0.47v (176) except on the hottest days, where it reads a little higher. I never changed it to the infinity settings as so many things in the ECU are dependent on ECT reading, I didnt want to rock the boat.

V: F
0: 223
0.16: 207
0.31: 190
0.47: 176
0.62: 163
0.78: 151
0.94: 142
1.09: 131
1.25: 122
1.4: 113
1.56: 104
1.72: 97
1.87: 90
2.03: 82
2.18: 77
2.34: 72
2.5: 66
2.65: 61
2.81: 55
2.96: 50
3.12: 45
3.28: 39
3.43: 34
3.59: 28
3.74: 21
3.9: 16
4.06: 10
4.21: 5
4.37: 0
4.52: -4
4.68: -8
4.84: -9
4.99: -11

 

[bogle]

At the time I purchased this ECU, it was state of the art. Right until two weeks later when the Infinity was released.

This is a worry of mine with even the "latest" stuff now. The infinity and the haltech 2500 are 10+ and 8 years old respectively.

 

[Valhalla]

Thanks to bogle and Old Guy for the info. Here are three tables of my coolant temps from V2. The first one is what came from AEM as their default;


This next one is using the plot values that Old Guy supplied;


Notice how the AEM default file rises slowly as you approach 260F and also how, as the volts increase it sets for -58F! What the hell? Even I know that is not right.

With the values that Old Guy supplied me, the plot is more linear until you get above 176F and then it starts to ascend more rapidly. This plot has the range of ascent inclining as the temps get hotter. I don't think that would aid in accuracy at the most critical temps are approached. Just my $.02.

Here is the table with bogle's AEM Infinity scale and see how that compares.

We currently have an NSX in the shop with an Infinity ECU and the SOS twin Turbos and it has no temp issues running almost the exact cooling system I have. This table, seems to me, to look the best without having such abrupt changes at either end of the voltage. I'm meeting with Chris Wilson from SOS tomorrow and will compare. I'll report back with any progress.

 

[Old Guy]

I posted that spreadsheet with the NSX sensor values as an indication of what the NSX sensor 'voltage' curve should look like. I created it by scaling resistance values off of the resistance versus temperature graph for the sensor in the service manual.

View attachment 171245

The graph in the manual is literally just a nudge over 1" x 1" in size and to make things interesting when scaling off of it the resistance axis is a log10 scale. If you look at the graph, at 212 F the line is thick enough that the sensor value could be 175 ohms (bottom of the line) or 218 ohms (top of the line). Valhalla is concerned about how hot the coolant temperature is running and around 212 F the uncertainty created by the line thickness is almost 50 F. Under normal operating conditions a 50 F difference is the difference between being just fine and having to shut it down. To add to that, there is production differences between sensors that results in a variation between sensors. At low temperatures the production differences are not significant. At high temperatures where the resistance of the sensor is quite small the production differences can become significant. If you want to have accurate temperature measurements at high temperatures you need to actually measure the resistance versus temperature characteristic for the sensor you are using.

OEMs don't need to have an accurate curve for the ECU sensor resistance at high temperatures because they don't use the ECU sensor to control anything at high temperatures. The coolant temperature sensor is used for engine starting and warm up fuel enrichment which ends around 20C - 40C and after that its not used for anything (except perhaps limp mode detection). There is probably a reason that Honda offloads the radiator fan control to a completely different sensor and device (the fan control module).

The sensors used are thermistors and are tailored to work in specific temperature ranges. This is an example of some OMEGA thermistors

Plat Res Temp Det-T30-Z (Page 250) (omega.com)

At the bottom of the 2nd page you they provide the resistance change between 90 C and 99 C for some of their sensors. Sensor 44004 gives you a 49 ohm change between 90 C and 99 C while sensor 44008 gives you a 668 ohm change. If you are operating around 95 C , the 44008 is going to make it much easier to detect changes in temperature.

Short answer:
- the data in my Excel spreadsheet was illustrative and definitely should not be used if you want to use your ECU for high temperature measurement. It would work just fine for cold start and the warm up cycle because accuracy is less critical for the warm up process
- you can potentially get reasonably accurate high temperature measurements if you measure the actual resistance versus temperature values for your sensor using a hot water bath

If you alter sensor calibration values, keep in mind @bogle 's comment:

I never changed it to the infinity settings as so many things in the ECU are dependent on ECT reading, I didnt want to rock the boat.

The Infinity value for the NSX sensor provided by Bogle is 4840 ohms at 38 F. The value for the NSX that I eyeballed from the service manual curve is 6000 ohms at 32 F. Resistance increases at lower temperature so the Infiniti value is probably not that far off my value at 32F. I don't expect that the change would make a material difference to cold start and warm up; but, if a lot of fine tuning went into the start and warm up routines you might notice a slight difference if you alter the calibration values.

A significant point of interest is what is the AEM programming interface doing with the sensor voltage calibration curve that you enter. It would be theoretically possible that the ECU accepts the data as a look-up table and that every time the ECU reads the voltage on the sensor the firmware jumps jumps to the table and sorts through the table to find the applicable voltage range and then interpolates to find the actual temperature. That would be computationally intense; but, doable if you have processor speed and particularly if you have a special purpose processor with physical units set off to handle critical functions. A much more computationally refined process would be for the interface software to accept the voltage calibration data you enter and then calculate the coefficients for a three coefficient equation which simulates the calibration curve and then up load the three coefficients to the ECU. This allows the ECU to do much faster / streamlined calculation of temperatures in real time. The down side is that it can result in errors at the extremes of the curve - the problem I noted in my first post. That is something that you might want to check into because getting an accurate sensor calibration curve is not going to fix that problem.

As a last resort, if you can't sort out the temperature sensor calibration, one possibility you might want to consider is to find someone who has a moderately new mid to high range Fluke (or similar) digital multimeter. Most recent Fluke multimeters come with a type K thermocouple probe for measuring temperatures. The probe is thin enough that you can slip it under the hose on the thermostat housing exit to get a good measurement on the temperature of the coolant exiting the block. If you want extra security use a banded clamp in addition to the spring clamp to really tighten the hose over the thermocouple wire. The thermocouple lead should be long enough to feed into the NSX cabin so you can read temperatures while driving; but, if it isn't type K extensions are available.

 

[bogle]

you can potentially get reasonably accurate high temperature measurements if you measure the actual resistance versus temperature values for your sensor using a hot water bath

This and the fact that, IIRC, the ECT and IAT sensors share the same resistance chart in the manual (along with the chart for all honda IAT sensors), maybe a measured IAT scale will be helpful, just as another data point. I did measure a brand new honda IAT in my build thread. I noted in the thread (and forgot until I just reread it) that it was similar to the s2k scale you found:

Ohms, Temp (F)
4100, 50
3570, 55
3100, 61
2950, 63
2880, 64
2480, 71
2320, 73
2100, 77
1965, 80
1937, 81
1900, 82
1650, 88
1400, 95
1250, 100
1200, 102
1185, 103
1060, 107
1050, 108
895, 115
810, 120
720, 126
660, 130
585, 136
520, 142
455, 149
405, 155
372, 160
328, 167
300, 172
284, 175
261, 180
235, 186
221, 190
210, 193
200, 197
193, 199
180, 202
175, 204
162, 209
158, 212

And the AEM voltage table for a 2.2k resistor

Volts, Temp (F)
0.00, 284.00
0.16, 270.78
0.31, 218.06
0.47, 187.92
0.62, 169.95
0.78, 154.80
0.94, 143.12
1.09, 133.70
1.25, 125.09
1.40, 117.29
1.56, 110.29
1.72, 103.97
1.87, 97.80
2.03, 91.98
2.18, 86.72
2.34, 81.04
2.50, 75.13
2.65, 70.98
2.81, 64.93
2.96, 59.74
3.12, 54.18
3.28, 48.69
3.43, 42.75
3.59, 36.17
3.74, 28.71
3.90, 17.93
4.06, 7.15
4.21, -2.97
4.37, -5.39
4.52, -6.82
4.68, -8.35
4.84, -9.89
4.99, -11.00

 

[Valhalla]

OEMs don't need to have an accurate curve for the ECU sensor resistance at high temperatures because they don't use the ECU sensor to control anything at high temperatures. The coolant temperature sensor is used for engine starting and warm up fuel enrichment which ends around 20C - 40C and after that its not used for anything (except perhaps limp mode detection). There is probably a reason that Honda offloads the radiator fan control to a completely different sensor and device (the fan control module).

Short answer:
- the data in my Excel spreadsheet was illustrative and definitely should not be used if you want to use your ECU for high temperature measurement. It would work just fine for cold start and the warm up cycle because accuracy is less critical for the warm up process
- you can potentially get reasonably accurate high temperature measurements if you measure the actual resistance versus temperature values for your sensor using a hot water bath

Thanks so much for all of your help and wisdom. That is why I use prime everyday. it's to read, learn, help and ask for help. I love you guy's.

Your spreadsheet mimics very closely the Infinity curve. As the AEM ECU uses this for warm up and to pull timing if it gets too hot, I wanted to be sure the readings I'm getting thru the canbus were actually true numbers. As the standalone ECU also controls fan on and off, it was kind of critical to make sure the Engine Coolant Sensor worked and was calibrated to the AEM ECU. So I uploaded the Infinity Coolant Sensor Calibration file and took a drive.

Ambient temps were low 90's so a bit cooler than yesterday but i do feel the numbers are more in line. The fan kicked on at 185F (where I had it set) and the coolant temps read 186-192F. I stopped at a light and it settled into 190F which is thermostat full open. Never went above 192F but this was street driving and not track use.

At this point I feel somewhat better that the temperature sensor is properly calibrated and reading a fairly true number. I will do further testing to confirm those numbers. Once confirmed I'll revert back to the main reason I started this thread, the car is running too warm and I need to upgrade my cooling system. probably starting with a new, larger capacity radiator. Arizona summers are not going to get any cooler and I would like to stay on track more than 4-5 laps. Thanks everyone for your help and guidance. Now to search for a big radiator.

 

[Valhalla]

i did meet up with Chris Wilson of Science of Speed fame, yesterday. He looked over my ECT file and confirmed it was pretty damn close to the one SOS created by actually testing the sensor. Only off on two way points by a total of 3F. Congrats to bogle for this file. Much appreciated.

He also confirmed my temps were pretty normal for even a fully stock C30 motor with Arizona ambient temperatures. Hotter than I would like but he stated my paranoia was due to the added knowledge as I had a new Can bus gauge and I was actually able to see real temps. It seems the OEM stock gauge reads the same reading from 180-215F regardless. So if that needle starts to move you better pay attention quick. That being said, I have added my name to the back log of customers ordering the newest version MASIV radiator. My luck it will arrive in January.

 

[bogle]

Well good to know the infinity scale is close to what SoS recommends. I’d love to see their measured scale. This also inspired me to buy a new oem sensor and measure it out of curiosity. The differences at the upper end of these scales are pretty large. I realize there’s still that variance with small ohm changes but would be good to have a benchmark. I’m also on that masiv list, can’t wait to replace the oem rad.

 

[Valhalla]

Well good to know the infinity scale is close to what SoS recommends. I’d love to see their measured scale. This also inspired me to buy a new oem sensor and measure it out of curiosity. The differences at the upper end of these scales are pretty large. I realize there’s still that variance with small ohm changes but would be good to have a benchmark. I’m also on that masiv list, can’t wait to replace the oem rad.

I think your scale is pretty bang on. the difference in those two way points could simply be me trying to plot volts on the AEM scale and not being able to precisely place the numbers. But off a total of 3F over two points is damn close, close enough for me anyway. Thanks again.

 

[RYU]

Working on it! Hopefully not as far as January as it seems the world is on the right side now of this Delta thing.

 

[bogle]

I bought a new 37870-PJ7-003 ECT sensor and measured it from 60F to 212F. My readings were close to the infinity ohms scale. A couple degrees lower around operating temp, then a couple degrees higher between 60F and 150F.

Ohms: F
2860: 60
2430: 70
1935: 81
1535: 93
1310: 100
1055: 111
920: 117
770: 128
690: 133
540: 146
480: 153
417: 161
380: 167
315: 178
285: 185
254: 192
220: 200
200: 207
180: 212

In the AEM voltage range:

V: F
0: 263
0.16: 244.1
0.31: 226.37
0.47: 198.04
0.62: 178.83
0.78: 162.66
0.94: 149.54
1.09: 139.47
1.25: 130.26
1.4: 121.59
1.56: 113.49
1.72: 106.55
1.87: 99.86
2.03: 93.92
2.18: 87.73
2.34: 80.99
2.5: 74.8
2.65: 68.72
2.81: 60.8
2.96: 53.73
3.12: 46.24
3.28: 41.04
3.43: 36.24
3.59: 30.63
3.74: 25.35
3.9: 19.72
4.06: 14.09
4.21: 8.34
4.37: 2.19
4.52: -3.57
4.68: -5.75
4.84: -7.63
4.99: -9

The setup. At each temp reading, I'd make sure the thermometer and the sensor were stabilized for 15-30 seconds. I also had a 2nd 'fast acting' thermometer I'd put in the water to make sure everything agreed before noting the resistance.

 

[bogle]

Working on it! Hopefully not as far as January as it seems the world is on the right side now of this Delta thing.

Definitely when they are ready for an order, I am in!

 

[Old Guy]

The setup. At each temp reading, I'd make sure the thermometer and the sensor were stabilized for 15-30 seconds. I also had a 2nd 'fast acting' thermometer I'd put in the water to make sure everything agreed before noting the resistance.

The approved testing method used by laboratory's the world over!

Your significant other is OK with that re appropriation of eating utensils, or is this a case of what they don't know won't hurt them :smile:? To avoid the risk of being caught in flagrante I used some cut up coat hangers for the same function.

 

[bogle]

Haha! As long as everything is new and there’s no oil involved she’s ok with it. Though I only had a small time window to measure. After that I was “in the way” and hassled for all the wires everywhere. I didn’t go lower than 60deg because it would have required an ice bath and more time. A couple ice cubes got me to 60, so that was the lower limit. The whole time I was getting “What are you even doing?” She def didn’t understand the why. Cmon, I’m doing science, you know?

 

[Valhalla]

I know a thing or two about being "in the way". I use the same line when she is in the garage!