Problem with seperate 12V temperature meter

sid86 · 03-13-2019, 02:51 PM

Hi all,

I'm having some troubles with getting a little 12V (oil)temperature meter to work correctly. The meter is this one: cheap from China

I attached the meter on a switched power source (+ in the fusebox, and - from the negative of one of the footwell lights). The car is a 2009 987.1 S.

- When I attach the sensor to the meter, and attach the meter to a stand-alone 12V car battery, everything is working fine. It shows the temperature and updates every second. Great! However, I don't like carrying an extra 12V battery with me;
- When I attach the meter to the cars power system, it shows an ERR message. When I use a multimeter, it showed 11.6V (probably because I drained it a bit with the doors and trunk open). Starting the car makes no difference, still the ERR message. The meter should work on 8-30V.

Do these cars have something special on the electrical system, like a canbus-error-check that's disturbing things? I can't seem to discover anything out of the ordinary when spending my time watching a multimeter. It's stable at 11.6V.

Help is appreciated. I prefer oil on my hands instead of this electrical stuff

TimT · 03-13-2019, 03:36 PM

I'd cut my loses and toss that thing...

Pick up something like:

Scanguage ll

You can read and clear codes, you can set the display to display most of what is on the CAN bus.. you can even customize what data you display, if you know certain codes etc..

jdavis7600 · 04:33 PM

The owner's manual for the Scangauge II that is online does not say anything about the ability to use it to measure oil temperature.

It's more expensive than the Chinese product, and I've no experience with one, but you might want to talk with Pedro about the oil temperature gauge he sells here:

http://pedrosgarage.com/Site_2/TechnoGauges.html

sid86 · 02:05 AM

Thanks for the replies. I don't really like an analog gauge, it seems out of place in the interior and they are too big. Hence the reason I chose a digital one. I used a 'Datona' (?) meter in the past which was perfect (on another car though), but I couldn't find it anymore.

Nevertheless it's strange that it works perfectly on a stand-alone 12V battery

EDIT: a Scangauge won't show oil temperature on the 987.

sid86 · 03-14-2019, 03:11 AM

I believe the temperaturesensor is an inductive type. I'm not sure of how this works, but could it short out through the engine/chassis back to the negative of the battery? Therefore not being able to measure?

jdavis7600 · 03-14-2019, 08:25 AM

Quote:

Originally Posted by sid86

Thanks for the replies. I don't really like an analog gauge, it seems out of place in the interior and they are too big. Hence the reason I chose a digital one. I used a 'Datona' (?) meter in the past which was perfect (on another car though), but I couldn't find it anymore.

That's interesting to read. I installed a combination digital clock & digital oil temperature gauge on my Ducati Monster, but it was a Daytona, not a Datona. You can't see the Daytona name on the gauge because I covered it with black tape.

When I just now Googled Daytona oil temperature gauge, I found several sources, including this one: https://japan.webike.net/products/1328333.html

Perhaps something like it will work better for you.

TimT · 03-14-2019, 08:40 AM

Quote:

The owner's manual for the Scangauge II that is online does not say anything about the ability to use it to measure oil temperature.

Actually it does, it might be a little work to dig up the HEX code that provides the oil temp info on a Porsche, the attached link is a generic set of commands to enable display of Oil temps..

Yes it is more expensive,, but it is a powerful programmable tool.. I have custom gauges for my F250PSD, and Subie WRX, I haven't used it in my Cayman yet, as I have access to an Autologic blue box if I need to scan or reset codes..

Scanguage Oil temp commands

sid86 · 03-15-2019, 02:49 AM

Thanks jdavis7600, indeed it was the Daytona: Digital WATER or OIL TEMP GAUGE | FTZ Racing

Loved this thing. I think I will get this one again. Hopefully it will work with the sensor so I won't have to replace it again, it was an absolute

to fit.

FYI, I used the same location as Gator Bite on the Planet-9 forum (don't know if linking is allowed). This will only give an adequate reading when the engine is running. When the engine is off, the sensor isn't submerged in oil anymore and its readings will spike heavily. Nevertheless I prefer this location compared to something underneath the car.

@TimT: thanks for the info. It seems like a little more effort to get to work properly. Nevertheless I'm looking forward to your review in a Cayman

tcora · tcora's Garage

This is an interesting challenge.

Is the oil temperature sensor already installed in the engine? I wonder if your ground circuit is not a good one. When you say that you measured 11.6V, am I correct in assuming that you measured that voltage at the power inputs to the meter?

sid86 · 03-16-2019, 02:23 PM

Quote:

Originally Posted by tcora

Is the oil temperature sensor already installed in the engine?

Yes.

Quote:

Originally Posted by tcora

I wonder if your ground circuit is not a good one. When you say that you measured 11.6V, am I correct in assuming that you measured that voltage at the power inputs to the meter?

Yes.

I tried one more thing: used a stepdown regulator from 12V to 3V. I soldered 2 wires on the 2032-battery connectors, and connected the stepdown meter. When connected to a seperate 12V battery, it works fine. When connected to the cars electrical system: error.

The sensor has 2 wires, I assume a positive and a negative of some sort?

11.6V should be good (I now measured 12.1V with the battery charged). The meter should (...) work with 8V to 30V.

For now I have the battery back in and everything works OK. The downside is the battery only lasts for 3 months. Hence the reason I wanted to connect it to the cars electrical system.

tcora · tcora's Garage

Hmmm. As a diagnostic aid, I'm going to suggest that you run the ground wire for the display unit back to the engine (same location that the sensor is grounded) and see what that does for you.

tcora · tcora's Garage

sid86: any news to report?

sid86 · 04-03-2019, 02:45 AM

I tried another meter today with the same sensor, because its a challenge to replace it. It doesn't work and gives the same result. I blame it on the sensor shorting out through the engine block.

Another solution may be a meter/sensor using only 1 wire for the possitive instead of the 2 wires coming out of the current sensor. However, I'm thinking of leaving it as it is. The only downside now is having to replace the battery every 1 or 2 months.