Help me monitor the transmission temperature of my minivan

[SEMark]

Here's a bit of a long shot, but maybe you all can guide me in setting this up.

I want a way to monitor the transmission temperature of my minivan while pulling a trailer. Ideally it would be the fluid temperature, but I think I will have to settle at best for the case temperature.

My thoughts:
Use a thermocouple of some sort and have a conversion available to calculate what specific voltages mean in degrees F.

My experience:
I've never fully built an electronic device, but I have a solder station, wire, etc. I have desoldered and soldered circuit boards. It doesn't scare me (too much).

Constraints:
I don't want to spend $200 to achieve this. I'm hoping to be under $40.
I have a multimeter that I could use for this.
The van has 12V available of course, or I could batteries. Also have a 7.5W 120V inverter I could use.

Alternatives:
It's been suggested I should just buy a meat thermometer and call it a day.

I'd love to hear your thoughts!
Thanks

[jcgoodman]

I'd think about the physical connection between your device and the transmission first. Where are you going to put the thermometer? Drilling holes in important parts of your car is probably unwise: is there a way to put a sensor into the transmission fluid reservoir and lead a wire out? Putting the sensor on the outer case of the transmission is probably going to be very inaccurate.

For temperatures above boiling you'll want a thermocouple and thermocouple amplifier. That plus an Arduino, an LCD display, and some assorted bibs and bobs should do you. The Arduino can run off your car's 12V. Project cost will probably be over $40 but less than $100.

[zener]

Some vehicles have this information available through the OBDII connector. What year and model are we talking about? Otherwise the BBQ sensor down the dipstick sounds like a decent starting point.

[SEMark]

Thanks for the responses. Some great points!

Van is a 2004 Pontiac Montana

I don't want to drill anything in the aluminum transmission. My thoughts were to either mount a thermocouple probe in a protected location on the outside of the case (with heat soak / delay / accuracy issues) or to splice a rubber hose and add a fitting with some sort of thermowell.

But, I never thought of going down the dip tube! Seems a little scary, but actually quite doable. The tube diameter is large compared to the dip.

On the OBDII side - yes, that might be a possibility too! I know there is no dash display for this temperature, but rockauto sells a replacement "Transmission Oil Temperature Sensor" so the ECM is likely getting this information. Any idea how I can extract it?

Thanks!

[zener]

On the OBDII side - yes, that might be a possibility too! I know there is no dash display for this temperature, but rockauto sells a replacement "Transmission Oil Temperature Sensor" so the ECM is likely getting this information. Any idea how I can extract it?

It appears the info is available on the OBDII connector. Here is some info from the ScanGuage site:

http://www.scangauge.com/support/x-gauge/gm-specific/

The easy way to get it is to buy the ScanGuage II, which will cost you $170, almost the exact amount you said you didn't want to spend! However, the thing is so cool I think you would be happy once you have it. It can monitor this and a lot more.

Now if you really want to roll your own, there is a chip called ELM327 that is pre-programmed to interface to the OBDII bus. I think it is basically a OBDII to RS232 converter. You can do some searching on that. Here is site I found that has some other OBDII interface products you might use.

http://www.elm327.net/

[SEMark]

On the OBDII side - yes, that might be a possibility too! I know there is no dash display for this temperature, but rockauto sells a replacement "Transmission Oil Temperature Sensor" so the ECM is likely getting this information. Any idea how I can extract it?

It appears the info is available on the OBDII connector. Here is some info from the ScanGuage site:

http://www.scangauge.com/support/x-gauge/gm-specific/

The easy way to get it is to buy the ScanGuage II, which will cost you $170, almost the exact amount you said you didn't want to spend! However, the thing is so cool I think you would be happy once you have it. It can monitor this and a lot more.

Now if you really want to roll your own, there is a chip called ELM327 that is pre-programmed to interface to the OBDII bus. I think it is basically a OBDII to RS232 converter. You can do some searching on that. Here is site I found that has some other OBDII interface products you might use.

http://www.elm327.net/

Thanks so much for this reply. Lots of reading later, and I now have an ELM327 on it's way to me. I have an android phone, so this plus Torque Pro will get me all that I need and more, for less than $20.