dan_189

[rant] Very annoying you can't get oil temp out of a generic OBDII unit and Torque! It's probably one of the most useful temps to know seeing that there is no gauge for it.

Time to jump ship to a 997 and ditch the volt gauge!!

I also like that the digital speed gauge is in the centre too like the MK1 why did it get moved to the left! [/rant]

Porschetech3

I agree wholeheartedly, oil temp is a MUST HAVE on a car if you are going to track it any at all. The only thing I like more on my 99 996 over a 997 is the throttle cable and no PSM nanny's lol

dan_189

Indeed!
Although I'm fly by wire but don't have PSM although no track time for me so I'm disadvantaged without it for street driving theoretically!

Back to the gauge though Grrr I wish there was a factory one haha
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tomcat

Porschetech3

When they say they can't "crack the code", they are referring to the Porsche specific protocol that PIWIS , Durametric, and ICARsoft uses to get oil temp data (all data) through the OBDII port. The standard OBDII protocol is public information ordered by the Feds but unfortunately the Feds didn't order the oil temp data to be mandantory, SMDH

Porschetech3

Recap:The overall methods of procuring an oil temp gauge

Aftermarket digital temp gauge or analoge temp gauge or mechanical temp gauge : Digital temp gauge can not be hooked to factory temp sender due to high impedance effecting signal ( from 900 ohm to 10k ohm) .Can be hooked to bank 1 head port opposite the bank 2 oil pressure sender, not the best location for temp measurement as this oil is after the oil cooler and before the oil has done any real work. Can be installed in oil sump, good location for temp measurement, but this is intrusive and would require drilling and taping of oil sump.

Aftermarket Digital Volt Meter; Can be hooked to factory NTC temp sender if resistance is 0.35Mohm or higher so it will not effect sensor values. Requires a cheat sheet to convert to Temp Fahrenheit.Not an actual Temp Display. Best place for oil temp measurement of hot oil returning to sump after work.

Custom build Digital Temp gauge: Can be hooked to factory NTC temp sensor using Ardunio low impedance processor. Requires electronic and programming skillz and fabrication of custom enclosure/housing for mounting. Best location for temp measurement at factory location. Not a DIY for a lot of people.

Conclusion is there is no ideal way to get easy install and best temp reading for oil temp. It would be nice if a Tuner/programmer could reprogram the OBDII portion of the DME to output the oil temp data on the PID of the OBDII data stream. Then it could be displayed out by Bluetooth on Torque App, or could be plug and play to the OBDII port for many OBDII gauges available.Of course this will never happen.
.

Ahsai

Yup,I pretty much concluded the same a few yrs back and nothing has changed.

Porschetech3

OK I started to give up and just stick with my indash DVM and cheat sheet, but found a little renewed drive and went ahead and ordered a Adrunio Nano v3.0..lol I also searched and found a 4 digit 7 segment display with 4 74HC595 shift registers and Enclosure,with the single DIN blank panel should look good. We will see how it goes. Ahsia I may need you to write that code since you are familliar, I think I can load it..lol

kbollaert

Sooo, with all of the discussion I'm somewhat confused. Does tapping into the dme feed using your original dvm change the output? I'm interested in the simplest solution that gives me an accurate result, and I don't mind the mental gymnastics required to use the cheat sheet. The arduino mod sounds interesting but I prefer to keep the interior as close to stock as I can.

Ahsai

Tapping the signal does not change the signal a bit provided you do it right, meaning whatever you connect to it needs to have a very high internal impedance. E.g., a good quality multimeter or aurduino. You may get away with you simple digital voltmeter table look up setup. The ultimate test is to see if the connection makes the Durametric reading change. If it does not, you are successful.

Yea, I love keeping the stock look hence the VDO analog oil temp gauge with aurduino.

Porschetech3

The little DVM that I used in my first project has an impedance of 0.35Mohm the effect and accuracy will be 2% at 100F(102F)1.1% at 130F(131.4F) .6% at 160F(160.9F) .3% at 212 (212.6F) It gets better with higher temp, I have measured the factory NTC up to 400F.

The oil temperature is only used by the DME to calculate Vario-cam.The vario-cam on the 3.4L is advanced at idle, then at 1200 rpm it is retarded by 12.5 degrees (25 crank), then at 5120 the intake cam is again advanced 12.5 degrees(25 crank). If the oil temp exceeds 265F the 1200 rpm switch point moves to 1480 rpm. All other calculations of the engine such as fuel, ignition timing, fans,ect use the coolant temperature.

I have read that the Arduino anolog input has an impedance of 1Mohm. If this is true the effect and accuracy will be .8% at 100F(100.8F) .4% at 130F(130.5F) .2% at 160F(160.3F) and .1% at 212F(212.2F) . It also gets better with higher temp and the Arduino is 3 times more accurate than the DVM.(0.35Mohm vs 1Mohm)

Either one will be plenty accurate enough in my opinion. The DVM requires like you said, "some mental gymnastics" (ie cheet sheet) ...the Arduino will be real temp display, and can be calibrated/programmed to be even more accurate if lab grade data is used, but I think anything within a couple degrees is good enough.

kbollaert

Many thanks to you both for excellent explanations! I'll go with the simple dvm (with a period of monitoring with my durametric) since I consider oil temperature a must have. The Arduino setup will be a nice improvement down the road, so to speak.

Porschetech3

Well I got the "cheap temp gauge" using Arduino Nano micro-processor and seven segment four digit LED display with 4 74hc595 shift registers working. I must say it is a nice, neat, and powerful little package. Has enclosure that will fit nice and blend well with dash in a blank single Din face-plate.

The accuracy should be dead nuts on. I used the Steinhart-Hart equation because I think it is what Porsche would have used to calculate their math, because it is more accurate than the Beta value , Defence R/T, or R/T equations. Then I used the Steinhart-Hart and the B- Curve Coeffecient in the program to do the math and should be the same math that Porsche uses as some of the values are carried out to 15 digits past the decimal. With using the same NTC sensor and same reference voltage, and this fancy math it should be dead nuts on what the DME is outputting to PIWIS/Durametric.

The Sketch program I wrote is 37% of the capacity of the storage of the Adruino Nano micro-processor and took me about 100 hours, but of course most of that was just a learning curve because I'm not well versed in writing computer code.But I did manage to write in a start-up program that starts with Por-....SCHE.....tempF, that's pretty cool. lol I got a video of it starting up and displaying temp of a hot cup of coffee and a cup of ice water, with the lap top serial monitor I can also display on the serial monitor the Temp, rawInput, NTC resistance. But the video is an mp4 and haven't figured out how to post it to the forum.

I should have it finished and installed and real life road tested compared to PIWIS/Durametric value sometime next week, stay tuned.

dan_189

​​​​​​Its awesome how far you've taken this! Great work.
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I think most people either upload an unlisted video to YouTube or host the video in Dropbox etc.

If you could incorporate this into an obd ii plug with a screen I'd buy one! Would have to be in Celsius though, hopefully not another 100 hours to recode it! :-p

Ahsai

I'm impressed! Can't wait to see the final product.