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Cheap oil temp guage

Old 01-07-2018, 11:58 PM
  #31  
Porschetech3
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Originally Posted by strathconaman View Post
Can you tell us what thermometer you have found?
The only one I found that comes close is this XH-B305F on E-bay. It is a USA seller but I'm sure it comes from Asia. Finding one that displays in Fahrenheit in stead of Celsius or Farhenheit/Celsius is very difficult, since most areas of the world use Celsius. And not many of these type things are made in USA.

If anyone finds one with like specs/function, but with a nicer/aluminum/carbon-fiber housing, or a nice housing to fit the Adrunio and display, let me know.https://www.ebay.com/itm/Thermometer...72.m2749.l2649
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Old 01-08-2018, 12:19 AM
  #32  
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What might make more sense than a gauge is something like this:

https://www.adafruit.com/product/879

but not sure how you could mount it in a car and not look ghetto.
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Old 01-08-2018, 12:34 AM
  #33  
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Originally Posted by boingolover View Post
What might make more sense than a gauge is something like this:

https://www.adafruit.com/product/879

but not sure how you could mount it in a car and not look ghetto.
Yes, that is the same problem with the Ardunio, it uses a display like this, and I haven't found a suitable housing that would not have to be custom made to fit. It needs to have a factory like housing that would not have to be hand made/
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Old 01-08-2018, 12:54 AM
  #34  
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Originally Posted by boingolover View Post
After trying to dig through that manual to find the DME pinout for my car, one thing's for sure: my hat's off to anyone who is a Porsche tech
Porsche repair manuals are, for numerous reasons ,by far the most challenging of the car manufactures. I spent 20 years as a Ford Master Technician, 10 years as a Mitsubishi Master Technician, and 14 years as a Porsche Gold Meister Technician, before retiring. I can honestly say Porsche manuals are by far hardest to follow .
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Old 01-08-2018, 07:32 PM
  #35  
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Well I am very satisfied with this XH-B305F Digital temp display, it is spot on all the way up to the 260F limit. I used some Canoloa Oil in a frying pan on a hot plate, and put an actual factory Porsche oil temp sensor in it while monitoring with the Fluke Infrared/Laser thermometer. It was 2 degrees off (low) at 50F but by 100F was spot on, and all the way to 257F was spot on, then the alarm sound and display was flashing but kept reading unil it reached 260F, then was flashing HHHH.Once the temp cooled back to 260F it started reading again but still flashing and alarming, then cooled below 257F it stopped flashing and alarming.

This display is a bit bigger than the DVM I had previously used so it will not fit in the batwing or in the switch holes beside the radio. I have a factory CD holder and Cubby, so the CD holder (I never use anyway) will have to go. Will use a single DIN blank faceplate to replace the CD holder , then cut the single DIN 76x40mm rectangle for the display. Will be any easy DIY and look factory-like.

Just to recap, you need the XH-B305F Digital Thermometer with a 45k ohm resistor install between the 2 sensor wires( cut off B3950 sensor , will not be used). Then the top sensor wire will tap to pin 73 in DME, the bottom sensor wire will connect to the black ground wire and then both will tap to pin 6 (ground) on the DME, and the red power wire will tap to pin 54 (12v switched) in DME.(note: these pin locations are for a 99 with DME 5.2.2 only) The whole thing will cost about 15 bucks and take about 1.5 hours to install. https://www.ebay.com/itm/Thermometer...72.m2749.l2649

FWIW even though the set up with the 45k resistor will match nearly identical to the factory oil temp sensor , there is a calibration mode that I found while playing with the Digital Thermometer and can adjust 10F up or down if need be. I would suggest installing then road test with Durametric or PIWIS tester to monitor oil temp and calibrate display if there is any deviation. The two buttons on the back are to set the high and low alarm setting and the calibration, but I think it is not necessary as the high temp default is 257F and the accuracy is very acceptable and good to go.https://www.ebay.com/itm/100-x-45k3-45-3K-Ohm-1-0-6W-0207-Metal-Metal-Film-Resistor/271976444671?hash=item3f530f32ff:g:ICoAAOSwcu5URoGeh

Last edited by Porschetech3; 01-09-2018 at 02:48 AM.
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Old 01-08-2018, 11:02 PM
  #36  
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Auber instruments. Programmable gauge is $50 and the transducer is lab grade with a range greater than what is needed here - already calibrated. I am installing the transducer in the bank 2 cam cover (opposite the oil pressure gauge). Plan is to use the gauge to trip the rad fans at a set temp. I think the gauge will fit in the bat wing between the seat heater switches. Waiting to get it laser cut.
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Old 01-09-2018, 02:24 AM
  #37  
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Originally Posted by tomcat View Post
Auber instruments. Programmable gauge is $50 and the transducer is lab grade with a range greater than what is needed here - already calibrated. I am installing the transducer in the bank 2 cam cover (opposite the oil pressure gauge). Plan is to use the gauge to trip the rad fans at a set temp. I think the gauge will fit in the bat wing between the seat heater switches. Waiting to get it laser cut.





That will work well to turn on fans, but the location is not ideal for oil temp measurement. I believe the factory oil temp sensor is in the best location to measure the hottest oil that is coming off the crank, rod bearings and pistons.

I love that little Display though, great quality and it is smaller than the XH-B305F , Its the size of that first DVM that I installed and will fit in the batwing, or in the blank button area. It looks like it may be compatible with the factory NTC sensor with an appropriate resistor. !! Good Find !! I think I will research this Display and see if it can be made to work with the Factory NTC.

edit: I researched that Digital Display and it is not compatible with the factory NTC sensor. It is designed to work the VDO NTC sensor or with numerous thermocouplers or transducers, but the VDO NTC sensor resistence at 25C (77F) is 900 ohms and the Porsche factory NTC temp sensor is 16k ohms at 25C (77F).Cannot be made compatible , even with parallel resistors, unless used with the Ardunio like what Ahsia has done?

Last edited by Porschetech3; 01-09-2018 at 04:51 AM.
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Old 01-09-2018, 01:37 PM
  #38  
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Another option, more expensive is P3 Gauges. I talked to those guys and they said their gauge would plug into the existing wires. IIRC, it was calibrated per the Durametric-type data, I believe.

I agree, cam cover, especially Bank 1, is not a good indicator for temp. But I went this way for the alarm/output for the fans. From what I gather, unless you have a transducer in Bank 2 oil, all measurements are lower estimates of max temp anyway.
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Old 01-09-2018, 02:15 PM
  #39  
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Interesting Ptech3. Based on your description, you are merging the two active circuits together between the DME and the digital meter. e.g., does the DME also see the internal resistance (divider) of the digital meter and the 45k resistor? I'm just trying to understand how it works.
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Old 01-09-2018, 07:28 PM
  #40  
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Originally Posted by Ahsai View Post
Interesting Ptech3. Based on your description, you are merging the two active circuits together between the DME and the digital meter. e.g., does the DME also see the internal resistance (divider) of the digital meter and the 45k resistor? I'm just trying to understand how it works.
Ahsai, I had that same question that needed to be answered. Both circuits have the same 5v regulated potential, both circuits are looking for a path to flow with least resistance, this least resistance being the path through the factory NTC sensor to ground, since the Digital meter has a higher resistance/impedance it does not impede with the performance of the DME circuit.
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Old 01-09-2018, 08:49 PM
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Originally Posted by Porschetech3 View Post
Ahsai, I had that same question that needed to be answered. Both circuits have the same 5v regulated potential, both circuits are looking for a path to flow with least resistance, this least resistance being the path through the factory NTC sensor to ground, since the Digital meter has a higher resistance/impedance it does not impede with the performance of the DME circuit.
Thanks for confirming your circuits. Joining the two active circuits like that require detailed circuit analysis, then you can figure out what's going on on EACH component. What you said about the internal high impedance of a digital voltmeter (essentially what the digital gauge is) is not true in this case because I bet inside the gauge, there's an internal resistor just like the 8k resistor inside the DME that connects the sensor to +5v. By connecting the two circuits like that, the implication is the 45k resistor will be connected in parallel to the stock sensor. The internal resistor of the gauge will also be connected in parallel with the 8k DME resistor. That may mess up the Durametric reading because now all the resistors and thermistor have different values than expected. Also, the digital meter 5v supply may not be spot on, if it's just a little bit higher than the 5v reference of the DME, it will start pumping current into the DME...or vice versa.

I definitely would not recommend bridging the two active circuits like that.
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Old 01-09-2018, 10:38 PM
  #42  
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Originally Posted by Ahsai View Post
Thanks for confirming your circuits. Joining the two active circuits like that require detailed circuit analysis, then you can figure out what's going on on EACH component. What you said about the internal high impedance of a digital voltmeter (essentially what the digital gauge is) is not true in this case because I bet inside the gauge, there's an internal resistor just like the 8k resistor inside the DME that connects the sensor to +5v. By connecting the two circuits like that, the implication is the 45k resistor will be connected in parallel to the stock sensor. The internal resistor of the gauge will also be connected in parallel with the 8k DME resistor. That may mess up the Durametric reading because now all the resistors and thermistor have different values than expected. Also, the digital meter 5v supply may not be spot on, if it's just a little bit higher than the 5v reference of the DME, it will start pumping current into the DME...or vice versa.

I definitely would not recommend bridging the two active circuits like that.
I understand your concern and went down that same thought process to analyze the circuits. The Digital Meter does have an internal resister of 10k ohms like the DME has at 8k ohms. To explain my analysis of the circuits think of them in terms of water flow.

You have 2 100ft garden hoses, you hook one to your house(5v potential) to the front spigot (DME) with a restricter washer (8k internal resistor) and run to your driveway. Then hook the other hose to the back of the house (5v potential) to the rear spigot (Digital meter) with a restrictor washer with a smaller hole (10k internal resistor) and then a small leak to the ground (45k resistor) and run to the driveway. At the driveway hook both hoses connect to a Y and to a garden sprayer ( factory NTC) spraying to ground. When the garden sprayer is spraying, both hoses are seeing the same pressure drop (voltage drop).No water is being pumped back into the house front spigot (DME). The flow and pressure(current and voltage) of the front spigot (DME) is not effected by the connection to the rear spigot (Digital meter).
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Old 01-09-2018, 10:59 PM
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You are assuming the DME reference and the digital meter reference are exactly 5.000v. Anyhow, that's not the most critical issue assuming the two references only differ a little.
What you are doing is like halving the DME internal 8k resistor to 4.44k (8k parallel with 10k). The 45k parallel with the thermistor is not doing much at higher temp when the thermistor is only hundreds of ohms (45k parallel with something hundreds of ohm will not affect it much at all). The end result should be at the same temp, the voltage will now be higher than before because signal voltage = 5v x (R2/(R1+R2)), where R1 is the DME internal resistor and R2 is the thermistor resistance. R1 has been reduced from 8k to 4.44k. That also means the temp displayed by Durametric will not be correct because the DME internal resistor has been halved essentially.

Back to your garden hose analogy, the two hoses definitely provide different pressure drop (lower drop) compared to a single hose.

BTW, can you remove the 10k resistor on the digital meter? If you can, the DME internal 8k resistor won't be affected and you will be using only the high impedance part of the digital meter to read the signal voltage.
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Old 01-09-2018, 11:32 PM
  #44  
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Originally Posted by Ahsai View Post
You are assuming the DME reference and the digital meter reference are exactly 5.000v. Anyhow, that's not the most critical issue assuming the two references only differ a little.
What you are doing is like halving the DME internal 8k resistor to 4.44k (8k parallel with 10k). The 45k parallel with the thermistor is not doing much at higher temp when the thermistor is only hundreds of ohms (45k parallel with something hundreds of ohm will not affect it much at all). The end result should be at the same temp, the voltage will now be higher than before because signal voltage = 5v x (R2/(R1+R2)), where R1 is the DME internal resistor and R2 is the thermistor resistance. R1 has been reduced from 8k to 4.44k. That also means the temp displayed by Durametric will not be correct because the DME internal resistor has been halved essentially.

Back to your garden hose analogy, the two hoses definitely provide different pressure drop (lower drop) compared to a single hose.

BTW, can you remove the 10k resistor on the digital meter? If you can, the DME internal 8k resistor won't be affected and you will be using only the high impedance part of the digital meter to read the signal voltage.
You are forgetting the DME and the Digital meter both take their readings AFTER the internal resisters (8k and 10k). The internal resisters are connected to the 5v potential EACH, therefore are not connected in parallel?

As for my water hose analogy, maybe it would be more correct to use a pressure regulating device that reduces pressure with higher temperature,regardless of flow volume, instead of a garden sprayer.

Last edited by Porschetech3; 01-10-2018 at 12:15 AM.
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Old 01-10-2018, 12:04 AM
  #45  
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I'm not forgetting anything but I have failed to explain it clearly.

You can do a very simple test. Read the oil temp using Durametric (with the gauge disconnected) then quickly connect the gauge and check Durametric reading again. It should read LOWER oil temp now.
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