seeking input: automatic transmission temp gauge mod kit

(note: I may decide to make kits to install this mod and sell them. If I do, I will most assuredly become a sponsor, and there will be a sizable discount)

After my transmission overheated without a single warning light on my instrument cluster, or even really showing a temp increase, I came up with the idea for this modification - a few extra sensors on the transmission fluid cooler lines and a small module that installs on the back of the gauge cluster that allows the OEM temperature gauge to display the temperature of the transmission, instead of just the coolant temperature. It would have a button similar in look/feel to the odometer button and 4 indicator LEDs under the temp gauge - "engine", "transmission in", "transmission out", and "auto cycle". In each mode the gauge cluster would display the temperature read from the corresponding sensor, while in auto cycle mode it would cycle through all three sensors every few seconds, allowing hands free operation.

Anyone else want something like this? I'll be prototyping one for myself, if there is enough interest I may become a sponsor and sell them. Parts cost would likely run around $40 to $50 (electrical components $10, plumbing/sensor install kit $20, custom PCB $10-20 depending on how many I order), member cost would be approximately $50 to $60, and I haven't decided full non member price, probably in the $100-150 range.

I'm really trying to gauge interest here - I'm finishing the design and building one for myself regardless, but I want to figure out how many people would be interested so I can decide whether it will be economical to become a sponsor and sell the kit, or if that would be a money losing proposition.

If you can pull it off nicely, you bet I would.

Have you ever seen the bi-color LEDs that allow color blending? For example this board uses green/red bi-color LEDs on the left edge that let the lights smoothly transition from green to yellow to orange to red. It's very smooth and not "stepped" at all.



Anyways those might be useful. I've been thinking about ways of replicating the old System Sentry thing and they seemed like good candidates so maybe useful for you too

I would be in

This is interesting, but I would recommend having a setup with a stand alone gauge also.

Johnnie: You can already get standalone gauges - though I could easily implement something like that in the space ehall noted above.

Eric: definitely useful info, I have a clock module that I'm working on at the moment but haven't managed to find a full system sentry module anywhere. I've seen the LCDs but hadn't seen the ones with RGB backlight LEDs yet, could probably build something like that by setting up a rudimentary PWM driver for each LED color in a small microcontroller.

bmpweXJ - it should look pretty close to OEM, if not exactly like OEM, except for possibly the legends for the indicators themselves, which I haven't figured out yet. The whole control module should be about 1x2" I think, maximum of 1/4" thick (i.e. it should be possible to simply double face tape it to the back of the gauge cluster), the relay switching module will be around the size of a smallish cellphone and should be mountable almost anywhere under the hood, and the sensors will be coolant temp sensors installed in brass flare fittings. A line flaring tool should be the only required specialty tool, though I guess you could install it with hose clamps in the rubber lines instead if you wanted.

As soon as I finalize the design for the relay control logic I'll probably breadboard one up and install it, see how the ECU takes to it, then post pictures. Might be a week or two.

Would this just be available for 97+ xj's?

It should be available for anything with an AW4 (or for that matter any vehicle with an automatic transmission!) - the old Renix system with the split coolant temp sensors would actually be even easier, though I haven't checked to see if the temp/resistance curve for the gauge sensor on the Renix is the same as the unified sensor's curve for HO engines.

with a toggle switch takes about 15-20 seconds to settle on a reading. depends on how for apart the readings are.

Interesting. That might throw a wrench in the works somewhat... I'll have to experiment.

I'd be interested, if it would work in a 2001.

kastein said:

Eric: definitely useful info, I have a clock module that I'm working on at the moment but haven't managed to find a full system sentry module anywhere. I've seen the LCDs but hadn't seen the ones with RGB backlight LEDs yet, could probably build something like that by setting up a rudimentary PWM driver for each LED color in a small microcontroller.

Click to expand...

I wasn't talking about the backlight but instead the four colored LEDs on the left edge of that panel. They are dual-LED with individual brightness feeds that let you sweep between A-B. If you are talking about your own board you might consider something like that for ~engine and ~tranny lights that are green/orange/red according to temp, it would get you down to two visible LEDs

It should. I'm not sure the auto switch mode will really be relevant with the apparent runtime averaging of the temp reading by the ECU, from what Orange is saying. I'm curious though, because when I force my e-fan on or put my transmission in neutral and rev the engine to speed the mechanical fan up, I see the temperature start dropping immediately. I'll know more for sure as soon as I get the prototype built and test it out - or for that matter as soon as I get bored and rig up a toggle switch to my CTS temporarily.

EDIT: oh hey, didn't even notice that ehall... really neat idea. Hmm...

96 xj stock gauges, temp sensor at back of head which wires Direct to gauge. (stock circuit prior to 97?, later xj 's go thru PCM). Added toggle with second temp sensor in engine oil line. Probably just the oem gauge moves slow.

Good Luck,
Orange