Oil temp gauge using the built-in oil temp sensor

Hi folks, Just wanna share with you it's possible to convert the stock DME oil temp sensor signal to drive a VDO 300F oil temp gauge. Takes about a dozen electronic components, a microcontroller, and 8 lines of Arduino code. I used Duramatric to map the oil temp to the analogue sensor signal (tapped from the DME but no splicing needed so the whole mod is completely reversible), then I just made a circuit to drive the gauge based on the analogue signal. I figured out the different voltages needed to drive the gauge on the 5 diff temp settings on the gauge then just mapped those to the signal using a quadratic equation (implemented in the microcontroller). Alarm/LED warning based on programmable oil temp can also be added if needed. I have not mounted the gauge but the photo below shows how it can be mounted in the single DIN slot with a proper face plate. I tested the gauge and it's very accurate. This may be too much trouble for most people but I can share more details if there are interests. A good project if you have a thing for electronic projects 0804141906a (Medium).jpg 0804141902 (Medium).jpg

Very cool!

Very interested. Can you please share more details with me. Thanks.

Nice job. I've always wanted an oil temp gauge for my 996. Subscribed.

Oh you could build 50 for sale. Use a smaller digital flat gauge to better more subtly fit 996 interiors. Need an investor ?

I am EXTREMELY interested, I have been asking everywhere for this for years !!!! you are a savior I am totally interested but I would need detail info as I know nothing about electronic but I am a qualified geek . If you decide to sell the gizmo put my name on the list !

HOLY CRAP! That's COOL! Do you know what the PID'S are? I think if you know that, you can put custom PIDS into some OBD readers on the IPhone and such and see the Oil Temp.

Knowledge is power.

Dude you are a mad scientist... Cool mod!

Thanks guys! Give me some time and I'll do a more detailed write-up. @mikeborden, unfortunately the PID is not available for the regular OBDII ISO9141-2 protocol (which any generic OBDII reader uses). The PID is only available via Porsche protocol and h/w (e.g., Durametric). It will involve some serious reverse engineering (at least for me) to get the digital oil temp info from the DME. If someone knows how, please do share.

More photos in the meantime...these are demo photos, not the actual connectors 0622141816a (Medium).jpg 0622141815 (Medium).jpg 0622141814a.jpg 0623141915.jpg

Very nice bit of engineering. So this basically uses the factory input, saving someone from running a separate sensor and line into the cabin? Personally for the effort involved, I'd rather try to find a good stock tap in point for a sensor and run the wiring through with aftermarket gauge kit. Although I wear a pager and no cell phone so I might as well run a hot oil line into the cabin and do it really old school. J/k Nice job either way.

Quotes source post: 11556570

Correct because tapping into an engine oil port that has oil flow (to get accurate measurement) is not trivial (to me at least). Like I mentioned it's not for everyone for the effort but if you're a bit geeky or electronic savvy, it's not bad at all

I have a spares VDO gauge like that sitting around, as well as a soldering iron. I'll be making one as soon as you post a parts lost and instructions.

Ok, here's a very long write up. Enjoy **DISCLAIMER: Use the following info at your own risks. I'm not responsible for any damage to your car or your self-esteem Things you need: A) DME female pin x1 and male pin x1. http://www.mouser.com/ProductDetail/...LHPnvMw0tP4w== http://www.mouser.com/ProductDetail/...ge2OikIF63U%3d B) VDO Vision 300F Oil temp gauge ($30) or VDO regular 300F oil temp gauge ($20) (I highly recommend the Vision instead since it uses backlit lighting and it matches the rest of the stock gauges very well) Amazon.com: VDO 310106 Vision Style Electrical Oil Temperature Gauge 2 1/16" Diameter, 300F: Automotive Amazon.com: VDO 310106 Vision Style Electrical Oil Temperature Gauge 2 1/16" Diameter, 300F: Automotive 0805142057 (Medium).jpg 0805142045 (Medium).jpg C) The driver(~$15) (see the schematic for parts needed) D) A programmer to flash the ATtiny85 micro-controller $10 Arduino nano from eBay and these links http://arduinodiy.wordpress.com/2012...-arduino-nano/ ) http://forums.4fips.com/viewtopic.php?f=3&t=1080 E) Arduino IDE (free download here http://arduino.cc/en/Main/Software ) ======================================================================== ========================================= Explanation of how everything works together. 1) Oil temp signal from DME plug III/Pin 5 This signal (relative to ground) varies from 0-5v. Higher the temp, lower the voltage (NTC type sensor) e.g,. 1.8V=120F, 1.0V=165F, 0.5V=210F. Using Durametric, I figured out the voltage<->temp mapping (100F to 220F). 220F is the highest I could get my oil temp up to. I just added (0v=300F) based on my estimate and used the Excel trendline to extrapolate the rest of the range (220F to 300F). More measurements above 220F can increase the extrapolation accuracy even further. Drawing1.jpg 2) VDO Vision 300F Oil temp gauge This gauge has 5 terminals - "+", "-", "S", and two terminals for its light bulb. The "+" is connected to the 12v ignition power and "-" to ground. "S" is normally connected to a VDO temp sensor then to ground. Without the VDO sensor, we can still drive the gauge by supplying regulated 9v to "+", and applying variable voltage to the "S" pin to get different gauge temp readings. 3) The circuit The principle is very simlpe. The circuit supplies the correct voltage to drive the "S" pin of the gauge based on the oil temp sensor voltage input. The tricky part is how to figure out this mapping and how to implement it digitally (easy calibration). There are two voltage regulators U1 and U2: 5v for the micro-controller (ATtiny85) and 9v for the gauge and the opamps. The input signal feeds the opamp buffer U4 (1:1, no amplification) to ensure negligible current drawn from the DME (thanks to the extremely high input resistance of the opamp). The output of the opamp feeds the micro-controller's U5 input pin. The micro-controller then converts this voltage (0-5v) to a PWM singal. The simple RC low-pass filter (R2 and C4) then filters this PWM signal to a steady DC voltage that feeds the second opamp U3(with a x2 amplification) to drive the gauge. ExpressSCH.pdf ExpressSCH-page-0.jpg 4) If you use the VDO Vision (or regular) 300F Oil temp gauge, you can just flash the ATtiny with the code below and follow the inline instructions in the code. You can skip 5) and 6) below. 5) 9-point Calibration First load a calibration flash that just implements a direct mapping (i.e., Vout = Vin) to the ATtiny. Then use the potentiometer (SW1 set to "Calibrate/Test") to simulate the oil temp sensor signal and feed different Vin to find out the voltage levels needed for the 9 diff temp marks (i.e., 120, 160, 180, 200, 220, 240, 260, 280, and 300F). Then from the Excel curve in 1) above, figure out how to convert the oil temp signal to this voltage. Then load a new flash that implements this conversion (turns out to be a quadractic equation) to the ATtiny. Drawing2.jpg 6) Testing Set SW1 to "Calibrate/Test", adjust the potentiometer to diff voltage in 1) and verify the gauge's reading is correct. Flip SW1 back to "Active" and the driver is now ready. 7) Tap into the DME (reversible and no splicing needed) Just solder a "Y" or "T" wire between the two pins in A) above. Remove the DME PlugIII/Pin5 and insert this piece between the socket housing and the oil temp sensor green/red wire. Insulate any exposed metal parts appropriately. Tug it away and zip tie it neatly. 0806140930 (Medium).jpg 0805140831 (Medium).jpg ======================================================================== ==================================== The Arduino Code /* VDO Vision oil temperature gauge driver (7/31/2014) by Ahsai Tap the DME NTC oil temp sensor voltage reading of 2003 Porsche 996 (0 - 5V. High voltage = low temp) Reads an analog input, converts it to voltage, then converts the voltage to voltage_out using a function (based on Durametric reading, gauge calibration data and Excel spreadsheet trendline equation). Write voltage_out to analog output pin D1, as a fraction of 5.0v, to drive the VDO gauage */ // the setup routine runs once when you press reset: void setup() {} // the loop routine runs over and over again forever: void loop() { // read the input on analog pin A3 and convert the analog reading (which goes from 0 - 1023) to voltage (0 - 5V): float v = analogRead(A3) * (5.0 / 1023.0); float vout = 2.0; // To ensure the needle stays below 120F when the temp is below 120F //y = -0.3023x2 + 1.3098x + 0.294 if (v < 2.0) { vout = -0.3023*pow(v,2) + 1.3098*v + 0.294; } // If using a non-Vision VDO oil temp gauge, comment out the previous line and uncomment the following line //if (v < 2.0) { vout = -0.2352*pow(v,2) + 1.3098*v + 0.3117; } //float vout = v; // Uncomment this line for calibration // convert vout (0 - 5.0V) to output (0 - 255) and write to D1 analogWrite(1, (int)(255.0*vout/5.0)); delay(100); }

DUDE! Are you a computer nerd? That's quite awesome though! Mike

Haha, no, I didn't even know what Ardunio is a few wks ago! It only looks complicated but the principles are very simple. It's a lot of work for this mod but half of the fun is the process of learning and creating Hope someone will also enjoy it like I did.

I'm a software guy, so I'm digging that aspect of it. If you ever need to add moving averages, regression to the mean, etc. hit me up, but I'm guessing you'd have no problem w/that.

Quotes source post: 11558706

There's quite a bit of different API's available for the Arduino boards. The last one I did for a friend that tied in his universal TV remote to an Arduino to control a motor allowing him to rotate and tilt his tv stand. That one was all done in JavaScript programming. It's all really just inputs and outputs. Sense an input and program some logic on what output you want to send a voltage or signal based on certain criteria's.

I really hope someone pick that data and build something ready to install. I may try the DIY way but I'll have to wait for the fully documented DYI as I know nothing on electronics

Quotes source posts: 11559614, 11559746

Yes, it's quite simple once you know what it's doing. Actually more design is needed on the analog circuits surrounding the micro-controller. I tried to use just a simple opamp and implement the mapping using analog but the calibration is a nightmare and it's not accurate either. So mc is the way to go with its flexibility to be re-programmed and re-calibrated when newer data points (225F+) are available. Phil, I knew you've been asking and waiting for this forever. Will let you know if I ever develop it further to something more readily installed. As is, it does require some electronics knowledge unfortunately.

You are our only hope

Don't know how I missed this thread - I've been looking for something to do with my old 'Duino since I started playing with the Pi. I think I might go with an Adafruit LCD display instead of the gauge, but what an awesome hack. I love it.

Quotes source post: 12692118

Thanks! Digital LCD display will be even easier. All you need is the first temperature vs voltage function in post #15. I never get around to complete mounting the gauge but I researched quite a bit and finally found a stock looking gauge panel to fit the CD holder rack perfectly (single DIN) $20 here http://www.ngpracing.com/newstore/42...olf-jetta.html It's very well made and the texture matches very well with the console. You will need some creative way to mount it (maybe use some springs) and also decide what to put in as the second gauge but I think it will look quite nice when finished.

The usual Ahsai brilliance ! Well done Ahsai -you've added more useful,usable tech to the 996/M96 subject than most of us combined.This is just your latest. A prior Post asked about fitting an old school oil gauge. There is a convenient port on the cam cover.It is sometimes used by the IMS lube line kits. a.k.a. DOF.This could be used for a sensor or a simple oil line direct to a gauge ? This could be just a diagnostic connection.No need to run the oil line or wiring to the cab .

Quotes source post: 12692374

Thanks Schnell! I'm aware of that port but the drawback is it's at the end of an oil gallery so it's only good for sensing oil pressure and the oil flow there is not optimal. The beauty of this hack is it's using the stock oil sensor which sits in the sump, which sees the HOT oil dripping from the main bearings first hand. With this gauge, you can see the oil climbs up almost instantly when you race up a grade while the coolant temp gauge doesn't move at all (until much later when you slow down the car). I guarantee a quick response of the gauge to your right foot

Fantastic mod!! In the 997 they nixed the voltmeter and replaced it with an oil temp gauge. This is a great tool! Nice work!

From an ex-embedded software engineer, this is awesome!

Quotes source posts: 12704809, 12705054

Thanks, guys! Must be like a child's play for you then, Steve I just wish it's a bit easier to put together for an average DIYer. This is the best I could come up with w/o hacking into the Durametric way of retrieving data from the DME. BTW, since the hack I've discovered Porsche's documentation on the stock oil temp sensor temp vs resistance (R2) graph and from that, I was able to compute/derive the value of the internal resistor in the DME - 8k ohm (R1). The implication is with the temp vs R2 graph and known value of R1, we don't need Durametric for calibration at all and we can access the full range of oil temp without real oil temp measurements (which is difficult to produce unless you drive on a race track or you remove the sensor and dip it in very hot oil ) I drew a circuit diagram like this. oil-temp-sensor.jpg

Sorry if I missed this, but how did you identify which plug and pin went to the temperature sensor? I still want to do this mod to my 996, but more so I want to add a transmission temperature gauge on my cayenne for towing. So, I'll need to figure out the right pin for it, since it also has a built-in temp sender that the durametric can read.

Quotes source post: 12731964

I figured that out from the 996 DME pinout diagram. What year is your Cayenne? You need the pinout diagram of your Cayenne's transmission control module (under front passenger seat). I have the 2006 Cayenne transmission control module pinout: - pin 45 Green/Blue oil temp sense "+" - pin 8 Green/Gray oil temp sense "-" The two pins are connected to the two-pin temp sensor inside the transmission. You can apply the same principles of my mod so you have to plot the voltage on pin 8 and 45 while reading the actual oil temp from Durametric then decide which pin to use.

Thanks a lot; it's a 2004 but I doubt it's different than 2006. This project is on my long-term to-do list...definitely sounds fun.

I've just found this thread which seems to be exactly what I am looking for,however, I am not an electronics wizard so couldn't make the kit, fit it yes but thats all! Has this ever gone into production as a kit? Appreciate any replies. Thanks

Quotes source post: 12912332

A kit would be nice but I have no such plan though. I agree it's meant for someone with some background and interest in electronics. I wish it could be easier but if you want an oil temp reading with fast response, the stock oil temp sensor in the oil sump is at a great location for that as the hot oil from the main/rod bearings drips back to the oil sump.

Awesome job man. Count me as another that can't believe they missed this before! Now to convince the wife to let me modify her car. Maybe if I just show her the latest scored bore thread... Spent 12 years blissfully ignorant of oil temps, but now that my 958 shows it in digital and analog formats it drives me nuts not being able to see it in the 996. The BMW has always pissed me off that you get neither the oil nor water temps

Quotes source post: 12913481

Thanks gnat. I think it's due to cost saving for 996. Actually some bimmers are ok. A 2011 328i has the oil temp gauge front and center on the instrument cluster but it doesn't have voltmeter and coolant temp though. Btw, I measured the parasitic drain on that car and it was within a couple of mA (compared to ours tens of mA). No wonder their batteries last 6+ years. I guess their smart charging system pays off.

Ashai, Thanks for your reply. I will investigate a stock VDO gauge with sump sensor. Regards

Ok, I'm finally starting to understand this. As a poor man's hack, could you take a 0-5 analog volt meter and relabel it with a sharpie? The strange part would be the needle would read backwards since 0=300F but for $10 it might be dang handy to have for track days.

Quotes source post: 13555350

Yes in theory because of the high impedence of the voltmeter. It won't draw much current from the dme. However, the most interesting oil temp region is between 0 and 0.5v so unless you find a 0.5v voltmeter, the oil temp change won't move the needle much, literally.

Lol. So much for that idea.

Thus this one might work as poor mans hack?

Quotes source post: 13806689

Nope as the internal impedence of the analog voltmeter is too low. The DME won't be able to drive it from that oil temp sensor pin hence the digitial circuit I made.

Or for a REALLY REALLY poor mans hack , you just wire in a small red or blue digital voltage display next to a small list of pertinent readings ie. .5v-220f .4v=225f .3v-230f ect. http://www.ebay.com/itm/3pcs-DC-0-30...-/281308807040

Off topic, but since this data comes off the OBDII port, is there anyway to use one of the bluetooth OBD readers to pick up the data and send it properly? Why can the durametric read it, but my kiwi3 can't?

Quotes source post: 14114207

Two problems: 1) the data bus that allows the scanner to talk to the DME for this purpose is on a seperate pin than the regular OBDII pin 2) even if you can physically connect to that pin, the scanner still needs to speak the Porsche specific protocol (not OBD). It needs security authentication of the scanner before the scanner can even query the oil temp sensor value

if 1 is true how does the durametric pick it up plugged into the obdii port? Are there pins in there that generic readers dont use that durametric does? for 2 - theres no way to write that into some software? can't reverse engineer whatever durametric is using...

Quotes source post: 14114657

Yes to your first question and yes it's possible to reverse engineer durametric, which itself was reverse engineered from the Porsche scanners.

Quotes source post: 14115197

is the oil temp available on a 99 Boxster? Thx, mike

Quotes source post: 14328127

I think so because it also has the electronic oil level gauge, which uses a dual sensor to measure oil temp and level.

Great resource! This could be very simple using the $24 Cirtcuit playground. It has an arduino and some leds. Only need to wires to the sensor. Can probably be powered using the USB so only need a a charger for that, or bats. Would make a nice gauge. There is also a $5 case. You wouldn't see exact temp but I guess the range 200 - 300 is interesting. So each LED would be 10 degrees. https://www.adafruit.com/product/3000

Gosh I love reading these kind of innovations, I really do. Just wish I understood it. Keep up the good work guys and when the kits come out, then I understand simple 'plug and play' technology. I pay for the kits people create without question because of your-alls fantastic determinism and I appreciate that! .

Subscribed!

Another mod I'd like to have but will never see...

This is a great old thread that deserves to be revived. @Ahsai I�m guessing your pinout plug III pin 5 is referencing DME 7.8 I�m looking for the correct pin on DME 5.2.2, but my wiring diagram is not clearly legible. I can see the sensor is pin 13 in engine connector X59/2, (one of the round ones in the engine compartment) but I can�t read my diagram well enough to trace it back to the DME. Any advice/clues?

Quotes source post: 15677465

Hi Coopduc, the equivalent pin on your 5.2.2 DME is pin 73

That was fast! Thanks

@ahsai: can you elaborate a bit on the circuit in post 29? I assume the 5v reference voltage does not exist in the DME, so a simple circuit will need to be created maybe using a VXO7805 or LM7805 and a couple of 10mf capacitors, the R2 is the temp sensor in the engine, and V is the gauge? so an Arduino is not needed?

Quotes source post: 15685111

No, post #29 is just explaining how the stock DME/coolant temp circuit works. DME does have internal 5v signal. Anyway, it's not something you build. You need to build the whole circuit in post #15 so you can use a mechanical gauge.

So the signal on pin 73 (5.2.2 DME) is just the oil level/temp sensor output? And that output is an analog NTC signal? I'm looking to log oil temps to a race logger, but I read some thread about the output being an unreliable calculated value. Reading RL threads can get confusing when some authors content is not accurate. What pin is the input to DME from the sump sensor?

Quotes source post: 15909500

For 5.2.2, pin #73 is the one you want to tap into. It's an analog signal that indicates the oil temp (not oil level). It's a direct measurement taken from the oil temp/level sensor and it's NOT a calculated value. For your purpose, you just need to program your logger to map the signal (in volts) to oil temp. I have the graph in post #15.

Perfect, thank you.

I completely agree. I was thinking the same thing as I was this thread from the beginning. I have just enough electronic and software background to pull this off. Thanks Ahsai. It's on my long-term project list. I will post back here if I do an LCD implementation.

One more whacky late night thought on this project: could you hack a drain plug with a temp sensor wire through it, and an analog oil temp gauge hanging under the car, for stationary test that would calibrate the in-dash gauge with a direct analog oil temp sensor temporarily kludged under the car? I wouldn't want to test it moving, but a good 20 min warm up in the driveway would allow you to tune the calibration parameters more precisely. EDIT: never mind. Obviously you calibrate it with the Durametric readout. Duh.

A clean solution would be to use Racecapture for this, really makes sense if you have a phone/tablet in the car as a dash. It would be "easy" to get oil temp and oil pressure recorded and displayed. It would also be stored so that you could look at the data afterwards, you could then correlate oil pressure to G forces, RPM and such. Just like Ashai's solution you would "tap" into the analog value of the sensors. It also supports reading CAN values if somehow you can figure out what code that is. This is an example display, you can customize it: Here they analyze some data, here they have RPM/SPeed/TPS but you can change to anything. I think G force and Oil pressure would be an interesting combo. And also coolant and oil temps. https://www.autosportlabs.com/ We use it on our Miata race car, it's from 2006 so we read all the values from the CAN instead. On my megasquirt datsun race car I have a mix of CAN and analog sensors. Generally the HW is very good but the SW has some kludgyness, but it gets better. I don't track my 996 that much so haven't bothered with it.

Quotes source post: 16336835

I've done this to all my old ACVW's in the past and have wanted to do the same here but, I want a different location for the sensor.

The ultimate for me would be to replace the volt gauge with an oil temp gauge - like the Carrera GT! Who needs a volt gauge... facepalm Porsche, faceplam...

I'm looking to do this in the spring time! Thanks for the work and write up.., Would a t-cap connector work in getting the signal from the DME? Something along the lines of https://cdn.shopify.com/s/files/1/25...ors-Banner.jpg

you guys should get on fixing our water temps gage

Quotes source post: 11554601

all a bit to complex�s for me l think there is a tapping under fuel rail to fit sender as on a 3.2 2000 Boxer Engine . Thanks for reply.

My car came with this mod done using a digital display. While fiddling around with the center stack, the ground lead from the DME came loose. I tried to figure out where to place it on the board based on the basic schematic I got with the car. I�m afraid I may have messed it up as my display reads 8888 regerdless of which pin this ground is connected to. Anyone think they can help me out?

Ahsai, Just came across this thread. Did you add this to my ('old') 996 or the earlier one? Bob (IEEE Fellow who is very impressed)