Designing an Engine Oil Temperature Display Gauge Project

[17-CB-002]

Csory (Hungary), may be you can help in this project.
After reading from your (Csory) idea on building display gauge, I pulled out some info together on the design of an Engine Oil Temperature gauge.
By tapping into the actual "EOT" circuit between the ECM and the EOT sensor, one can read the ACTUAL oil temperature in "volts".
The reading should be anywhere between 4.9v "Cold" and 0.01v "Hot".
When referring to the Toyota ECT Voltage/Temp conversion chart, one can logically deduct the actual Engine oil temp..
As per the Toyota ECT Theory file- The ECM feeds a constant 5 volt through 2 resistors (One fixed inside the ECM and the second variable NTC resistor inside the EOT). All are BOSCH design.
Negative Temp Coefficient (NTC)- when the sensor is cold, her resistance is high and vise versa when it reads hot, the resistance drop).
In theory, at room temperature, one should read 2.2 volts and around 0.02 volts with a normal hot engine

Note: If you are checking the EOT voltage, you will require a "High Impedance" meter or the meter will affect the reading).

Good Luck.

Handy information is contained in these links,

https://i.postimg.cc/SQnXpVtd/2-A0-ABFF7...F930-D.png
https://i.postimg.cc/j2nYkDc6/39-D706-BD...A75825.png
https://i.postimg.cc/JtwCwRYf/9-C4-C1-EC...FD0-E1.png
https://i.postimg.cc/pV3mV8wH/A6-B63664-...-CBA41.png

[Csory_imp]

Alain: Thanks for the tip. Been toying with the idea but was a bit skeptical about tapping into the ECU's oil temp signal. First, I should be absolutely certain that one end of the voltage divider is connected to chassis ground (and not some sort of virtual ground provided by the ECU). The last drawing suggests this, but calling one half of the divider a "pullup" makes me a bit cautious. Another problem would be with the wiring/connectors: not sure if I could source a proper drop-in replacement, and just cutting/soldering in there is not something I'd expect anyone to do. Not even myself, at least not until the bike is under warranty Will take another look though.

[17-CB-002]

Hi Csory, in my previous job at a Japanese automotive OEM and before the diagnostic scanners were available, we back probe the wire at either the ECM or sensor depending on ease of component access & location. We often leave it there for days during troubleshooting.
There is no need to worry about the "pull up" resistor if you are using a high impedance meter. The "pull up" resistor selection depends on the scale reading the engineers want to see inside the ECM.

You mention the "virtual" ground: Inside the ECM there are 3 types of ground. One for the "Input" sensors such EOT, Intake Air Temperature etc. then there is the "Output" device ground such as Injectors or the Idle speed control air valve, ignition timing etc. and the last ground is for the ECM internal circuitry. Then all these ground wires goes to the chassis.

Can you build a "look up table" that can read the EOT in voltage (between 0 & 5v) and display it in temperature C or F ?

Tomorrow, I will shoot a short video to demonstrate it using a Digital voltmeter on my bike.

Would it not be nice if we can read the real exact oil temperature especially if we are stuck in traffic!

[GoldOxide_imp]

Past experience on previous CBs in parked traffic (think Caribana in godforsaken Toronto in July/August) was not the engine oil, but the hydraulic clutch. It failed to the point of uselessness. Had to have it cool down over 30 minutes to be useful again.

[Csory_imp]

Thanks in advance, Alain! (Lookup table, or even approximating with an n-level polynomial would not be a problem). Voltage measurement impedance on “my end” has the magnitude of megaohms - should not be a problem. The pullup worried me not for it’s existence, but for the particular word used. A bit of a layman’s term within a technical document - made me cautious about the credibility of the entire doc.

GoldOxide: was that steam bubbles forming in clutch liquid, or flex pipes softening up from the heat? Sounds rather ugly, being stranded for half an hour

[Bazbro_imp]

Thanks in advance, Alain! (Lookup table, or even approximating with an n-level polynomial would not be a problem). Voltage measurement impedance on “my end” has the magnitude of megaohms - should not be a problem. The pullup worried me not for it’s existence, but for the particular word used. A bit of a layman’s term within a technical document - made me cautious about the credibility of the entire doc.

GoldOxide: was that steam bubbles forming in clutch liquid, or flex pipes softening up from the heat? Sounds rather ugly, being stranded for half an hour

Yes, I'm curious about the reason you lost the clutch because of the clutch fluid overheating?
Maybe stainless braided lines could improve matters?
A good job it wasn't the brakes...
Mind you, that will never be a situation that occurs here in England, UK!!

[GoldOxide_imp]

Thanks in advance, Alain! (Lookup table, or even approximating with an n-level polynomial would not be a problem). Voltage measurement impedance on “my end” has the magnitude of megaohms - should not be a problem. The pullup worried me not for it’s existence, but for the particular word used. A bit of a layman’s term within a technical document - made me cautious about the credibility of the entire doc.

GoldOxide: was that steam bubbles forming in clutch liquid, or flex pipes softening up from the heat? Sounds rather ugly, being stranded for half an hour

Yes, I'm curious about the reason you lost the clutch because of the clutch fluid overheating?
Maybe stainless braided lines could improve matters?
A good job it wasn't the brakes...
Mind you, that will never be a situation that occurs here in England, UK!!

Yes, I'm curious about the reason you lost the clutch because of the clutch fluid overheating?
Maybe stainless braided lines could improve matters?
A good job it wasn't the brakes...
Mind you, that will never be a situation that occurs here in England, UK!!
This was on a CB750SC. The clutch line was not braided and I seem to recall the line going to the crankcase, which was immensely hot. I couldn't determine in-the-moment if bubbles were forming, but that would not surprise me if it did. I did not see any "steam-like" gases anywhere. The net-net was lever pressure was like "98%" lost and clutch plate action was immediate and no modulation control was possible. At the time I thought I blew the line from the heat.

I expect today's CB1100 would not have that problem, but I have not been in that situation with an air-cooled engine for quite some time either.

[flynrider]

Thanks in advance, Alain! (Lookup table, or even approximating with an n-level polynomial would not be a problem). Voltage measurement impedance on “my end” has the magnitude of megaohms - should not be a problem. The pullup worried me not for it’s existence, but for the particular word used. A bit of a layman’s term within a technical document - made me cautious about the credibility of the entire doc.

GoldOxide: was that steam bubbles forming in clutch liquid, or flex pipes softening up from the heat? Sounds rather ugly, being stranded for half an hour

Yes, I'm curious about the reason you lost the clutch because of the clutch fluid overheating?
Maybe stainless braided lines could improve matters?
A good job it wasn't the brakes...
Mind you, that will never be a situation that occurs here in England, UK!!

Yes, I'm curious about the reason you lost the clutch because of the clutch fluid overheating?
Maybe stainless braided lines could improve matters?
A good job it wasn't the brakes...
Mind you, that will never be a situation that occurs here in England, UK!!
This was on a CB750SC. The clutch line was not braided and I seem to recall the line going to the crankcase, which was immensely hot. I couldn't determine in-the-moment if bubbles were forming, but that would not surprise me if it did. I did not see any "steam-like" gases anywhere. The net-net was lever pressure was like "98%" lost and clutch plate action was immediate and no modulation control was possible. At the time I thought I blew the line from the heat.

I expect today's CB1100 would not have that problem, but I have not been in that situation with an air-cooled engine for quite some time either.

I have been stuck in mid-summer traffic on the CB11 a few times at temps exceeding 115F (46C). Never had an issue with the clutch, although I was beginning to get worried about the engine oil temp.

I've found that overheating on an air cooled bike (my CB11 or CB750) isn't really a problem unless you're stuck motionless and idling in temps above 100F for half an hour or so. Even moving slowly (i.e 10 - 20 mph) provides enough airflow to cool the bike adequately.

[GoldOxide_imp]

Thanks in advance, Alain! (Lookup table, or even approximating with an n-level polynomial would not be a problem). Voltage measurement impedance on “my end” has the magnitude of megaohms - should not be a problem. The pullup worried me not for it’s existence, but for the particular word used. A bit of a layman’s term within a technical document - made me cautious about the credibility of the entire doc.

GoldOxide: was that steam bubbles forming in clutch liquid, or flex pipes softening up from the heat? Sounds rather ugly, being stranded for half an hour

Yes, I'm curious about the reason you lost the clutch because of the clutch fluid overheating?
Maybe stainless braided lines could improve matters?
A good job it wasn't the brakes...
Mind you, that will never be a situation that occurs here in England, UK!!

Yes, I'm curious about the reason you lost the clutch because of the clutch fluid overheating?
Maybe stainless braided lines could improve matters?
A good job it wasn't the brakes...
Mind you, that will never be a situation that occurs here in England, UK!!
This was on a CB750SC. The clutch line was not braided and I seem to recall the line going to the crankcase, which was immensely hot. I couldn't determine in-the-moment if bubbles were forming, but that would not surprise me if it did. I did not see any "steam-like" gases anywhere. The net-net was lever pressure was like "98%" lost and clutch plate action was immediate and no modulation control was possible. At the time I thought I blew the line from the heat.

I expect today's CB1100 would not have that problem, but I have not been in that situation with an air-cooled engine for quite some time either.

I have been stuck in mid-summer traffic on the CB11 a few times at temps exceeding 115F (46C). Never had an issue with the clutch, although I was beginning to get worried about the engine oil temp.

I've found that overheating on an air cooled bike (my CB11 or CB750) isn't really a problem unless you're stuck motionless and idling in temps above 100F for half an hour or so. Even moving slowly (i.e 10 - 20 mph) provides enough airflow to cool the bike adequately.

I have been stuck in mid-summer traffic on the CB11 a few times at temps exceeding 115F (46C). Never had an issue with the clutch, although I was beginning to get worried about the engine oil temp.

I've found that overheating on an air cooled bike (my CB11 or CB750) isn't really a problem unless you're stuck motionless and idling in temps above 100F for half an hour or so. Even moving slowly (i.e 10 - 20 mph) provides enough airflow to cool the bike adequately.
The situation I experienced was a total trap:

* Parked on freeway.
* Off-ramps funneled to residential side roads parked.
* No natural air current.
* Super high summer humidity .
* Hot summer day.
* Moved only 100 feet in 30 minutes.

Had to take to the sidewalk to bypass the situation. Ironically, a police car came out of a residential laneway and cut me off - rightfully so. However, they didn't care. They were more concerned about the vehicular traffic situation as nothing moved on the asphalt. An officer got out of the car and asked me to push the bike, not ride it. Then they went to evaluate the traffic situation. Nobody was moving except pedestrians.

[Csory_imp]

As for the original idea, spent a few hours measuring the CB's (at least, my CB's...) built-in EOT sensor. The devil is in the details: if the same electronics are to be applied to bikes of different manufacturers, models or even model years, there has to be a guess made on which NTC thermistor is being used. Supply voltage might be different too - just too many variables I'd be comfortable to work with. There are some 50 or so standard NTC series, not sure if I could get a reasonable readout just by guessing. Of course it could be fine-tuned to any specific bike, but that would require some way to input points of the characteristic curve - basically, taking the EOT sensor out, dipping in a cup of hot water, and measuring temperature with resistance changes as the water cools down to room temp. Not something I'd expect to be a standard installation step