Drivetrain temperature sensors

I've been working on a making something for my truck for the past couple weeks as something fun to add as well as a way to feel like I've got something more modern than my 1995. It all started with me watching a very lengthy video by Banks Power on differentials and wondering what goes on temperature wise in the differentials. I've always had an interest in adding gadgets to my truck and felt this was a great starting point.

It's still in the early stages of testing but so far it turned out to work better than I could expected so soon! I first realized that adding a temp sensor to my rear differential was possible just from the sheer size of the filler plug and the fact that the fluid gets flung all over inside.

Luckily I was able to find a sensor perfectly suited to being installed into a drilled out fill plug.



Let me tell you drilling out the plugs with just a hand drill, even if it's a brand new Milwaukee, really sucks. I definitely need a drill press next time.

Either way I feel like the result came out very nicely. The sensor fit exactly into the center of the plug, almost as if they were designed to go together.



Next I did some testing with an ESP32, definitely my favorite MCU to use so far as it has a lot of power for it's small size, is very affordable, and includes both wifi and bluetooth. (OBDII anyone?)



I made sure to use a generous amount of wire as I would need to connect the sensor to my controller all the way from the differential into my cab.

After playing around with a few different icons and trying to figure out how to fit 3 different readouts on screen I realized that I would need a larger OLED.



I liked this one but it still wasn't the feel I wanted in the final version.





Yup that's more like it! Bigger is always better right?

I also figured out the aesthetic I wanted to go for, I was always partial to the retro future look that an OLED could bring. Those old 80s super car interior gauges were kind of my inspiration on this.



At this point you might have noticed I'm going for a 3 sensor setup. Sure the front might not be as important on the daily but I'm definitely interested in seeing what happens when I do use 4WD.

So the "final" step is to actually install the first version on my truck and see what needs adjusting, what I might have missed, and what the next versions will get.

To start since I used a factory plug everything fit just fine in the differential.



The really awesome thing I discovered since starting this project is that the trucks use the same plug size for every fill plug on the drive train. So my front and rear differential, transfer case, and transmission fill plugs can all have this sensor. Not only that but every truck since the "pickup" models has the same size plugs as well, so this would even fit on a 2016!

As a temporary setup I simply zip tied the wire up along the under side of my truck, I think going forward I will get some split tubing like the factory wires are in.





I also don't have the final plug that connects to the sensor yet so for now some normal header pins and a liberal application of electrical tape should suffice.



There was a conveniently placed gasket under the drivers side cab that allowed me to get the wires into the truck in line with where I needed to run the wires.



I disconnected the factory plug and pulled the entire assembly out so it was easier to work with.



I cut away the old tape and pulled my new wire through, then taped it all back together.



The wire feeds through under the drivers side seat, then I ran it along the other wiring to the left side kick panel and up through the dash to the center where my radio was. I forgot to take a photo of the routing here but I update it later.


Here is how it sits as of now. I threw away my old stereo as it was not functioning so I have room for this until I install my new one. I am working on a 3D printed housing to mount the screen flush somewhere on the dash in the near future.



I also don't have the front installed yet so the screen will show and X there for now. If another sensor accidentally gets unplugged or damaged I will be able to tell as an X will appear in that location as well. I'll be changing the graphics a bit over time to refine the look, and possibly add more information if I feel like it would be more useful to have that context.

For now though I already noticed a couple interesting things. My differential for one needs a little more fluid (oops), but also it seems because of this or because the rear diff is just smaller it will heat up a bit faster than my transfer case. So far it's only by a few degrees but the trend is there. The rear diff also cools down much faster as evident in my last photo, I'm sure that is a no brainer usually since it's got a lot less fluid retaining heat but cool to see with real number non the less!

I saw temperatures up to 220F on my drive from Forest Hill to Yuba City over the weekend, assuming I have the calibration correct that's higher than I would have guessed it would reach. If I were towing over a long period I would expect, from the numbers I've seen thrown around, to get 25k miles if I could maintain that temperature. Any higher and I would start losing some range.

I'll be updating this over time as I make changes, I do have plans to make a custom circuit board to replace the prototype breadboard I'm using now so that will look much nicer and be more durable.

 

Does the OBD in these older trucks have transmission and engine oil temp readouts? Would be cool to have those on display too.

 

I believe that they do have oil temp but not transmission temp available on OBDII. That's one reason why I wanted to put a sensor on the transfer case and transmission for my truck. I'll be playing with it more once I get that Bluetooth function setup.

 

This is an awesome idea. Will that 1.5" OLED fit where the clock is?

 

Sweet. Have you considered adding an ambient air temp sensor?

Would be really sweet if you could log the temperatures to your phone and have your phone attach GPS coordinates to each point. Plot those temperatures on a map might be valuable.

 

Awesome idea and execution.

 

Yeah it definitely could.

It would be pretty easy to add ambient air to this. OBDII has intake temp but also using another air temp sensor with a built in humidity sensor is pretty common. Where to mount it would be the most complex decision haha.

 

I like the execution and idea behind what your making but why not run temp strips.



I hit 180* on a quick trail run up to the mountains last weekend.

 

This is very cool! Look forward to seeing the project progress

 

Nice work! Looks good. Def reminds me of the old 4wd indicators. damnit now I want to make visual 4wd and locker indicators on an oled.
What's the benefit to watching your diff temp or is it just because? i haven't heard of anyone having issues in tacos dues to diff temps, and you def wouldn't wheel with it.

 

It would also be interesting to look at pressures in the rear diff, that way you would have a warning before blowing out your axle seals.

 

It should be the same as outside air pressure. If not, your diff breathers are clogged.

 

Yep, it would be a easy way to tell if they're clogged.

 

That's pretty cool, I didn't think to use the strips. I really wanted to know what temp the fluid actually gets. Last weekend I was able to place my hand on the diff cover and it felt warm while the interior temp was over 180F still.

Do you have an example of the old 4WD indicators? That's different than the little light on my dash that turns on when I engage 4WD right? I mostly wanted to make it for my own curiosity. I never realized the difference that the fluid temperature would make on the life you could expect to get from it so I wanted to see for myself how my truck did. I don't necessarily think it's an issue for my Tacoma as I will probably never tow, so it was more of a challenge for myself to see what I could make and how well I could integrate it.

 

You can also just look at them periodically. Diff breathers aren't one of those things that typically need a lot of attention, especially if you've installed diff breather extensions.

sensors seem like a lot of work for not much gain.

 

I started working on a custom PCB for my main controller. This is just the initial layout and there is more work to do before I can order the first sample for testing.



I still need to add in the programming pins so I can flash it, I will also break out more pins for extra inputs in case I want to add more features without having to wait for another board. I also ordered some of the initial components to test the circuit, specifically U3 which is the voltage step down regulator. Once I confirm that it will output 5V from 12V without issue I can order the initial batch of boards for me to populate and test.

I do plan to move all the resistors and caps to the opposite side of the main ESP32 board so I can make the entire board much smaller but for the first revision it will be easier to solder if everything is on the same side. It's also possible to change the design to fit into a gauge housing but I think I prefer a remote screen attached via ribbon cables.

 

What are you using for a voltage regulator?

 

That’s awesome! If you take this to it’s logical conclusion- a larger OLED, or multiple, replacing the gauge cluster. Have speedo, tach, all your warning lights, etc going through this.
Following this, can’t wait to see how this evolves!

 

I'm going to be trying an L7805 regulator. I've used another circuit with an LM2596 but they are a lot more expensive.

 

That works. If you're dropping it down from 14V to 5V though be aware that its gonna get really toasty if you put any real amount of current through it. I've used these little guys in the past with great results - far more efficient:
https://www.mouser.com/ProductDetail/Murata-Power-Solutions/OKI-78SR-5-15-W36-C?qs=uJpRT2lXVNXJP%2Bo08dQqJQ==


Another fun thought - if you add an IMU, you could have an inclinometer.