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Cheap oil temp guage

Old 12-03-2017, 06:34 PM
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Porschetech3
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Default Cheap oil temp guage

I have been wanting an inexpensive but accurate digital oil temp gauge that reads the same temp from the factory oil temp/level sender that the DME see's for quite some time.Seeing Ahsai's thread (and thankx to Ahsai for logging and graphing the temp voltage) on his oil temp gauge got me to thinking, but I don't have his electronic skillz to build a circuit board to convert the signal from voltage to degrees. So I got to thinking of how hard would it be for me mentally do the conversion. To my surprise, it is not hard at all. I started off with just one converted value 1.0v=160F

Then looking at the curved converted graph I realized that in the range from 160F to 220F there was correlation of about 10F to each 0.10v or 1F for each 0.01v.

I have a quick reference card that has 5 values/temps on it, that I keep close the the digital display, and a full conversion value/temp chart on my phone that I can pull up quick that has all values from 2.5v= 96F to 0.10v=290F

The digital voltage display is just a small voltmeter that is highly accurate to 0.0001v and uses 4 wires, 2 grounds and 1 12v power and 1 signalv. I ran a small 3 wire (22ga) cable to the DME and tapped on to a ground, a 12v switched power , and the oil temp wire (pin 73 on my DME 5.2.2).

On my 99 Coupe I install the display next to the radio in an unused button hole, and on my 99 Cab I mounted the display in the panel at the bottom of the console.

This is now one of my favorite gauges, right up there with the Tach and oil pressure.



By the way in the pics below the car was just stated and the oil temp is 96F(2.5v) on both cars, they will cruise at about 1.0xxxv - 0.9xxxv warm 160F-170F

Last edited by Porschetech3; 01-06-2018 at 09:34 PM.
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Old 12-03-2017, 06:42 PM
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dan_189
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Nice!

Have always wanted an oil temp gauge, well done
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Old 12-03-2017, 11:12 PM
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Yea it would be ideal if it had a plug and play conversion from digital volts to actual temp, but I'm not skilled enough to make a converter box for it. Here is a copy of my cheat sheet reference data.It may be a couple degrees off at some points because I rounded it off to nearest value. But I have driven it long enough that I have most of it memorized.
Attached Files
File Type: txt
oil temperature.txt (359 Bytes, 43 views)
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Old 12-04-2017, 09:38 AM
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nice installation! Where did you find the vm?
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Old 12-04-2017, 02:01 PM
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Originally Posted by kbollaert View Post
nice installation! Where did you find the vm?
The only volt meter I could find that met my requirement for size, resolution (0.01mv), supply voltage, and mounting, was an this E-Bay (China) one. Main drawback is it takes a long time to arrive.

https://www.ebay.com/itm/Red-LED-5-D...72.m2749.l2649

All that's required for mounting is a rectangle hole and it clips in. Accuracy is way more than necessary, I actually would not mind having one with a little less resolution to keep the numbers from constantly moving so fast in the lower digits.
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Old 12-04-2017, 02:17 PM
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Nice job! So what temp does 2.5174v equal? (your cheat sheet doesn't show up...)
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Old 12-04-2017, 02:38 PM
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Originally Posted by dporto View Post
Nice job! So what temp does 2.5174v equal? (your cheat sheet doesn't show up...)
2.5xxxv = 96F The engine had only been running a short time. Cold starts at 3.5xxxv and fully warmed up is 0.9xxxv

I wonder why my cheat sheet is not pulling up. It pulls up on my side, it is a. txt file?
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Old 12-04-2017, 02:45 PM
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Paul Waterloo
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You cheat sheet is a text file, I was able to open it in notepad:

0-300

.1-280

.15-270

.20-260

.25-250

.30-240

.35-230

.40-220

.45-215

.50-210

.55-205

.60-200

.65-195

.70-190

.75-185

.80-180

.85-175

.90-170

.95-165

1.00-160

1.10-155

1.20-150

1.30-145

1.40-140

1.50-135

1.60-132

1.70-128

1.80-125

1.90-120

2.00-115

2.10-112

2.20-108

2.30-104

2.40-100

2.50-96
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Old 12-04-2017, 03:40 PM
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How did you connect the voltmeter? Did you connect into existing wires or did you connect all the way back at the oil temp sender?
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Old 12-04-2017, 04:26 PM
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Originally Posted by turbogrill View Post
How did you connect the voltmeter? Did you connect into existing wires or did you connect all the way back at the oil temp sender?
I used a small cable with 3 22ga wires to the DME, then used Posi-Tap connectors to tap on to pin6(ground) pin 54 (12v switched) and pin 73 (oil temp sensor) about 4 inches from the DME. this is on DME 5.2.2(1999).... DME 7.2 (1999 c4 and 2000-2001 e-gas) DME 7.8 (2002-2004)will be different pins.Refer to appropriate wiring diagram.

Last edited by Porschetech3; 12-06-2017 at 07:28 PM.
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Old 12-04-2017, 05:31 PM
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Originally Posted by Porschetech3 View Post
I used a small cable with 3 22ga wires to the DME, then used Posi-Tap connectors to tap on to pin6(ground) pin 54 (12v switched) and pin 74 (oil temp sensor) about 4 inches from the DME. this is on DME 5.2.2(1999).... DME 7.2 (1999 c4 and 2000-2001 e-gas) DME 7.8 (2002-2004)will be different pins.Refer to appropriate wiring diagram.
Where did you find the wiring diagram?

I want to do the same thing but with oil pressure
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Old 12-04-2017, 05:43 PM
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It would be really simple to use a small arduino mini or equivalent and use a look up table or transfer function to convert this to temperature, also to add a button to swap from F to C

https://store.arduino.cc/arduino-micro
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Old 12-04-2017, 07:11 PM
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Originally Posted by turbogrill View Post
Where did you find the wiring diagram?

I want to do the same thing but with oil pressure
Here is an online workshop manual , it has the diagrams in it.
http://workshop-manuals.com/porsche/
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Old 12-04-2017, 07:29 PM
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Originally Posted by Chris(MA) View Post
It would be really simple to use a small arduino mini or equivalent and use a look up table or transfer function to convert this to temperature, also to add a button to swap from F to C

https://store.arduino.cc/arduino-micro
Simple?? lol ..ok...I got no idea where to start. I am basic electronic wise such as volts.ohms. resistance,diodes, resisters, transistors, ect,but when you ties a bunch on them together and then put a chip in, I'm lost.

If you could come up with a step by step SIMPLE instructions for a plug and play conversion box to put inline for this to display the temp, and take the place of the cheat sheet, it would be great !!
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Old 12-04-2017, 08:17 PM
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Cool setup. I like how it integrates into the bat wing.

You are not too far from the last step of using Arduino to implement that voltage to temp conversion. I used Arduino in my oil temp gauge thread.

This link shows you how to use Arduino to make a voltmeter.

http://www.instructables.com/id/Ardu...Voltage-Meter/

All you need to change is one line of code (the third last line) where voltage is computed. Instead of displaying voltage, you convert it to temp and display the temp instead. And once you've tested it, you can replace the big Arduino board with something very samell like the nano (like a USB drive size).
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