Porsche Head Temperatur sensor setup

[JoeMag]

Using aircooled porsche head temp sensor 993-606-013-00 with ECU sensor setup as Bosch 2500 ohm at 20C.

I'd heard of folks head temps getting up around 350F idling. My motor is race motor and teamp up to appx 314F and stops. So I figured I'd do test to see if it's maxing out... Well it was. Used a torch to gradually bring sensor by itself up in temp. As I suspected it stopped at 156C (~314F). Kept torch there to see if it would gradually go up, however, it didn't and obviously I went to high as sensor died.

Should I be using custom setup, or is Bosch 2500ohm at 20C correct setup? New sensor on order.

[David Ferguson]

What is your goal with this sensor? I believe Porsche only uses that for warmup enrichment. Once it reaches about 200f, they ignore it. For that purpose using the Bosch 2500 ohm @ 20c calibration seems to work.

Did you verify the calibration was accurate at boiling temp (212f @ sea level, less with elevation)?
Since that's a resistive sensor, you should measure the resistance at different temperatures to create a proper calibration, you could then create a custom calibration, perhaps with a wider range, but I believe the resolution will be very poor.

You might find that a PTC (positive temperature coefficient) sensor (PT100 or PT1000 type) would be better, vs the Bosch NTC (negative temperature coefficient).

[JoeMag]

I did not check the calibration. Will do that with the new one I'm getting.

Besides the warmup, it's to understand really what the head temperature is. If it gets too high, especially on a race motor, you need to figure out why. Greater chance of detonation or even melting parts. Maxed out at 314F is too low.

[David Ferguson]

What do you have as the diag low value for that channel? I am using .1V with one of my customer M84/911 engines.

I see the calibration for the Bosch 2500ohm sensor as going to 250 for the (C) calibration (which would be 482F), but only 392 for the (F) calibration. So I think the F calibration might be slightly wrong and the 0V line could be changed to 482.

I use the (C) calibration in the M84, but view the data in F in the dash, so that's probably why I've seen greater than 314F.

The way to view the calibration is to select it in the Input Setup, then select the "Custom" radio button and view the Table -- that will be the table for the sensor calibration you just selected.

[David Ferguson]

Sorry, I just realized this is in the M4 / M48 section. Process described above probably doesn't apply.

[JoeMag]

...thanks for the insight David.

fyi, I am using the C setup for the sensor in the M48 and reading it into my dash in F.

[rsscotty]

I have this calibration for a 964 CHT if that helps.

[JoeMag]

Thx RSScotty. That helps. Couldn't find data on web for anything higher than ~150C. Hopefully was just a sensor issue as that curve is what I have setup, Bosch 2.5k ohms at 20C.

[JoeMag]

Grabbed a breadboard with pot and went to town simulating temp sensor resistance changes to see what the canned "Bosch 2.5k at 20C" and the custom sensor set-up yielded as engine temp from the ECU. Graph says it all. ...above 300F canned senor setup is wrong.

Readings taken from ECU in C and I converted to F as I relate to that better.