Digital Thermometer DIY - Gen. 1

I've been meaning to install a digital thermometer in the Tacoma for months now. With winter here, it turns out I wouldn't mind knowing if it is 38 degrees out or 28 degrees out when I head into a curve that might be wet or might be coated in black ice.

So I got a cheap digital thermometer online for about $9. (Actually I got two, just in case. Now I need to figure out where else in my life I need 12 volt temperature readings.)

Took the thermometer apart, trimmed it a little with the Dremel, and installed it in the switch blank at the bottom of the center console. (What are those for, anyway?)

Tapped power from the aux lighter outlets so the thermometer comes on with the key. Ran the sensor out through the shifter access and attached it to the frame a few feet behind the driver side wheel.

Works like a charm. The only two rough parts of the installation came when I test-rigged the console & thermometer to the battery in the engine bay and proudly showed my wife that it worked. She told me it would probably make more sense to install it inside the truck since it would be both hard to drive with the hood up and impossible to read the thermometer with it in the engine bay.

The second rough part came when I did the final wiring test in the cab and thought I had fried the thermometer's chip because the readings were gibberish. It took me about five minutes to realize I was looking at the panel upside down.

 

Looks good, I like the display...clean.

I don't know if would make a difference, but typical sensors are located in the grill on many cars (BMW puts theirs in the cooling duct to the front brakes). You may get inaccurate readings if the probe gets coated with salt, dirt, mud or other crap.

 

I wanted to put it in the grill but didn't have long enough wires to reach. Thought about mud, snow, salt, all that. But figured if it turns out to be a problem I can always splice in more wire and route it all the way to the front.

 

yeah I see that thermometer wire getting coated in the dirt and grime of the world but other than that I like it.

might have to do this myself

 

The truck is about as grimy as it gets...hasn't been washed in about a month and has been driving through winter slop. So I figure the condition of the location on the backside of the frame support is pretty representative of how nasty it will get.

In any event, I'll keep an eye on things.

 

Nicely done, OP! (Your wife sounds like mine...)

 

Nice! I like it. I miss having a temp gauge.

 

Looks Perfect!!!!!!

 

Like the idea, how accurate is it? a few degrees off or ?

 

Well, sitting in the 50 degree garage it was very accurate. This afternoon on a trip to the dump it seemed a little high, so it is possible the sensor is reading some engine heat

Curiously, it's very quick to react to small temperature changes (going through the shade, down at the bottom of a hill, etc.) so I have a feeling that the ones built into cars have some algorithm that smooths out the second by second fluctuations. I know the temp readings in my other cars don't change as fast as this one does.

But to answer the question, it seems to read a little high. But I'm going out tonight and will see how it does in the cold and dark of a Maine winter's night.

As soon as I get more heat-shrink tubing, I will splice in a longer set of wires and run it to the grille where it belongs after all.

 

Here's the update:

I need someone with some electrical knowledge to give me an idea how to get the sensor to be more accurate. It's fine in the 50s (in the garage where I have verified the temp) but outside tonight when it should have read 14 degrees (brrr) it was showing around 29.

My theory is that because I had to lengthen the sensor wires (they were initially only about 5" long - far too short) I caused some kind of resistance that leads to incorrect readings.

I will re-do my sensor wiring in the next couple of days with cleaner solder joints, but I'm wondering if there's an electrical engineer who can give me any pointers. I've got a humanities background and we all know how practical that is around motor vehicles.

 

You are on the right track by reducing the resistance in your wiring. Sampling rate will affect the reading. The tricky part is finding a clean shady spot in the front end that is not affected by engine heat or thermal transfer.

 

Hey...looking at your pics...did you pull the lower console apart to get back there?

 

I like it! Been wanting one in my Taco for some time. Interested to see the final results.

Thanks for posting this up!

 

I did pull the lower console apart. Also took the trim from around the shifter so I could drop the sensor wire down there. Both are really easy to do.

I've been getting some crazy readings from the thermometer. When the engine is off I get temps that are accurate, but when I turn the engine on, I get readings 5-10 degrees higher. I don't think it is engine heat because it happens immediately, before the truck has a chance to heat up. And it happens again immediately when I turn the truck off (readings drop 5-10 degrees) when engine heat would set ill be an issue.

Mysterious. Hoping it will be solved with better wire and better solder joints. I will keep you posted.

 

I like this idea. Would you please link specific therometer you bought? I see some on eBay with extended sensors too.

 

Here's the link to the eBay seller:

http://www.ebay.com/itm/390718541238?ssPageName=STRK:MEWNX:IT&_trksid=p3984.m1497.l2649

 

Thank you for that. Here is one that seems to be the same physical size but has a much longer lead for the temp sensor.
http://www.ebay.com/itm/50-110-BC10...ultDomain_0&hash=item58aa427284#ht_3465wt_956

Perhaps it would be a good time to also install a clock in the adjoining switch blank. I cannot see the one on the dash as it is.
http://www.ebay.com/itm/0-56-Digita...ies&hash=item5d43cdc571&vxp=mtr#ht_3012wt_956

 

Andrew,

The problem with that one is that it's celsius. Other than that, it looks identical to the one I have. I'm thinking if I can't fix the sensor on my own, the $6 might be worth it just for the longer sensor.

 

This one is Fahrenheit and has a 3 meter long probe.

I just don't know where I'd mount it. Hmmm...