Hello all,

Following my previous thread, I have tested my bike's ECTS with my multimeter. I also found the service manual for the 2007 CBR125RW, and according to it, the values I measured aren't completely out of whack (I did a measurement before starting the bike, revved it a little bit and then did two measurements: immediately, and after a little while).

So here is my question: does anyone know the expected resistance of a CBR125R ECTS (part 37870KRJ901) for various temperatures (ideally a complete curve)? That same sensor is also present on many CBR models (and other Honda bikes as well, such as the CB1000R (various years), the CB600 hornet (also various years), etc).

In addition, I would have a corollary question: What is a sensible temperature range for the coolant? In whatever units really, I can convert. But I assume that anything between 0C and 100C at atmospheric pressure is fine? I suppose below 0 (water freezing temperature) is why the coolant has anti-freeze in it, and also that above 100C (water boiling temperature) is probably out of range? Unless the coolant somehow boils at a higher temperature?

Thanks!

 

That sensor is used in the following US models on this page. I don't have a manual for any of these models in order to tell you the temperature curves. Maybe someone else will.

https://www.partzilla.com/product/honda/37870-KRJ-901

 

Thank you for your response. I have found this page (when I looked up how expensive that part would be) but as you said, unfortunately, it does not have a datasheet. Nor do either of the other pages I found.

However, I found out that the aforementioned CBR125RW 2007 service manual does quote "80C (176F)" and "120C (248F)" coolant temperatures with the respective resistance ranges: 47-57 ohm, and 14-18 ohm. So, with the additional datapoint from another section of the same manual (20C/68F → 2.3K-2.6K ohm), I can now interpolate a curve, and also, it does answer my second question: the upper value for a sensible coolant temperature is 120C/248F (the lower one is whatever temperature the anti-freeze stop being effective at, which I suppose is several degrees below 0C).

Unfortunately, values above 100C make it impossible to test the coolant temperature sensor with water, as it would boil already. Therefore, I need to procure an electric heating element (an open flame would be a fire hazard) and use coolant mixed with water (1:1) in order to test it at such temperature...

I will update the thread with the curve I computed (I suppose, using a logarithmic exponential interpolation, given it has to fit the values above) as soon as I have it.

Edit: Ok so, apparently, the (exponential) interpolation is 8763.16 e^(-0.0637237 x). And here is the curve



Edit 2: Here are the extremum curves in case someone wants to see if their values are in range: 8335.97 e^(-0.0643838 x) and 9195.38 e^(-0.0631598 x).

Thanks for the contribution!

 

Remember that the Thermostat maintains the coolant system under (depending on the bike) 16 - 20 psi of pressure. That raises the boiling point, along with the 50/50 mix of antifreeze to be higher than 212 degrees F. On my F4i I'll see readings of 220 F before the radiator cooling fan turns on. The resistance of the CTS on the F4i at 120 degrees C is 0.65 k ohms to 0.73 k ohms. 650 to 730 Ohms is quite a bit different than the readings of yours.

 

This. This is why I post here. I would have totally missed the fact that the loop is pressurized. Indeed, that changes things. Well, thank you very much for pointing out what I missed. I will try to correct for this oversight and update the curves. Not sure how to do so without a specific pressure, but I'll try.

 

I'm not sure how it changes things. Only that the system can operate at temperatures above boiling and still be within "normal" operating temperatures. But that is not going to change what the resistance is with regard to temperature.

 

So, I checked, and the CBR600F4i 2006 does use the same temperature sensor (part 21). So what you are saying actually makes a lot of sense. However, I do not understand why the service manual specifies the values I reported above... Those are quite different from yours, too. How did you measure your ECTS's resistance?

Edit: Ok, sorry IDoDirt for doubting your numbers. As I specified when I mentioned it, the service manual I have is for the "2007 CBR125RW". I have checked what part it uses as an ECTS, and it turns out to be a different one, part number 37870KTF641. So, the values I calculated for the curve are potentially very different from the ones you measured. Also, if my values are matching the ones of the wrong part number, it would indeed mean my sensor is kaputt. Thanks for your contribution, you once again helped me.

 

I didn't take any readings from my sensor, I only reported what was in the manual from Honda. To me, the important thing is it doesn't overheat. If I do need to measure it, I'll toss it into a pan with a thermometer and measure it up until it boils. Then compare the readings.

 

I do not have a manual of my exact model. Could you please try to find as many datapoints as you can from your manual? ideally, 3 or more. I have found such data in the CBR125RW 2007 service manual. Hopefully you can find the same data in yours? That would be greatly helpful.

Thanks!

 

Here's what I've got.