Actual engine temperature vs diaplyed

If you're like me you may have once thought that the engine in your Cayman never really got too hot because the gauge never rose much over the 175 F mark; how WRONG! My water pump developed the first signs of its pending failure in the form of a very slight leak at the shaft seal [about 41K miles if your keeping score], and this fact prompted me to begin researching the entire cooling system for ways to extend the replacement's life. One aspect was to quantify the differences between the actual and displayed temperatures. I used my Duramtric to display the 'actual' engine temperature, and then recorded the value as the gauge's pointer crossed each of the markers on its face. The car was setting with its engine idling from a cold start. I also had a box fan blowing on the left front radiator opening. I stopped my test at 198 F because the rate of temperature increase seemed to have slowed, and besides, why purposely expose the engine to higher temps. FYI - this slow-down may also be related to how the Cayman 's double value thermostat functions at its maximum opening. For the attached chart I guessed that Porsche would likely design the gauge to become 'accurate' as the engine temperature approached the red maker at 250 F. Obviously this is but one test on a single vehicle, so the accuracy can't be judged. Still, the pattern seems consistent with previous experiences on a few other [non- Porsche ] vehicles, as well as numerous posts here and elsewhere. Most importantly, it suggest the need for real caution if/when your temp gauge ever goes up much above 'normal'. Finally, I suspect that the gauge's non-linearity is due to programming within the instrument panel controller, and therefore it cannot be 'corrected' via reprogramming of the ecu . However, I'm still trying to verify this theory and would appreciate hearing from anyone that knows any details.

Good to see an actual curve for this! Thanks! I have noticed this before though, from my odb reader, it seems that my engine likes being between 185-206 degrees. But the needle will not move an smidgen from 175 the whole time.

It's great to see information like this. Your suspicion that the raw temperature value is "conditioned" for human consumption is interesting. The fully technical term for "engine temperature" would be "coolant temperature at location X". (Where's X? Do we know if there is just one sensor?) (Off topic: for jet engines, there are standardized locations for temperatures. For example, "T4" is the combustor outlet - around 2500F. T3 - compressor discharge - is surprisingly hot, over 1200F. Jet engine performance comes from pushing those temperatures upwards, and that's how I made my living working as a "superalloy" metallurgist.)

If you check out my post from another thread, http://www.planet-9.com/987-cayman-boxster-chat/34162-water-temperature-accuracy-2.html#post629061 you will see that there's lot's of evidence that the dash gauge is a "sheet, I better stop because there's no coolant in my car" meter. Unfortunately stopping your data collection at 198F meant you missed all the real action. I commute and in summer regularly see temps over 200F, as high as 218F, but the dash meter stays steady at 175F! Never budges. I have yet to see a ScanGaugeII temperature that has caused the dash meter to move off 175F...Maybe it's broken? LOL

bruinbears , my research found that the Cayman thermostat is designed to reach full open at about 204F. And at that point the thermostat's secondary valve has closed off the bypass port which stops the flow of coolant thru the heater core. With all flow directed through the front radiators it should produce its maximum engine cooling ability. I wonder if that might help explain your observations of the temp only going up to the 206F range? drPhilGandini, I should have given you credit because it was actually your post that led me to conduct my test. FYI - here's what I've found as the 3 thermostat designs sold for our cars. In particular, some vendors incorrectly list the Boxter unit for the Caymans. While they are physically interchangeable, their operating temps are notably different. In fact, if I had a Boxter DD that I used year round in a region with cool/cold winters, I'd think hard about installing the Cayman thermostat. Boxter OE 186.8/210F Cayman S OE 181/204F Low temp units 160/est180

all modern cars don't display actual engine temp. that's why i'm using OBD2 reader to monitor the real temp. i kinda hoped that P car will show also oil temp, but it's not. only coolant temp is available...

in the factory tech info for the 981 they state the gauge reads 194F when the actual temp is between 185-221F. why have a gauge? why not a light cold, norm, hot?carl

I agree with Carl. An idiot light would be more appropriate than a gauge for how it's programmed. At least you wouldn't have the false sense of security that all is well that a gauge gives. I recently asked the local stealer service manager if it was possible to reprogram this gauge to read true using PIWIS . He looked at me like I was an idiot (could be) and told me that the gauge was accurate which as folks have found is not true. Porsche used to make gauges that read true. Must be catering to their perceived audience. This should be reprogrammable as the dash (or DME ) is just pulling it off the CAN BUS and manipulating for display. In the case of the older 987's I don't see a reason that the analog speedo couldn't be reprogrammed to read oil temp in deg C. The parameter is on the BUS. Might make it good for something. Regrettably this is outside of my skill set.

Car_guy: I really appreciate your testing, as there's really not enough of it. Many of us are "casual empiricists" including myself. I spent hours/days/months/years logging intake temperatures on my supercharged MINI Cooper S, and reported what I found. I haven't done so much with the Cayman as it's surprisingly "well behaved" from an intake temperature point of view (approaches are between +10F and +20F generally.) But the kind of information you provided is of interest, and sometimes value, to other Cayman / Boxster owners, and I certainly appreciate it. BTW, I am thinking of buying a Cayman GTS , and I notice it offers oil temperature and pressure with the display that comes standard with that package. <smile>

Some follow-up information... The attached images seem to confirm that the 987.1 Cayman engine actually has three temperature sensors. Values from these can be read by the Durametric and probably other ODBC2 devices, too. Actual engine temperature comes from the coolant sensor located on the coolant manifold at the front of the engine. The Intake Air Temperature sensor that's mounted on the intake manifold. The combined sensor for engine oil that reports level and temperature. PS - The PDK includes another sensor for the ATF temperature.

But no one has ever reported how to tap the oil temperature reading with a OBDCII scanner (like ScangaugeII). It would be great to read it.

I've used Torque (APP) on past cars... Haven't tried it on the Cayman yet... Maybe I can take a look at it tonight and see what information is available on it.

The 987 ECU outputs engine oil temperature on the CAN bus . dskogman uses his Aim Solo DL to monitor engine oil temperature this way. The CAN bus has a much higher update rate than the OBD data.

On the 981 , I know, not a 987 but perhaps somewhat relevant..........my oil temperature runs between 194 to about 204 in the summer in Florida depending on highway or around town. It does actively fluctuate at least seeming to indicate reflecting relative change vs. the water/coolant temperature which remains fixed at 194. On my 981 I run water, oil, oil pressure, and volts displaying at all times.

I am collecting oil temp from the Can bus and it is hitting 254 and I am trying to determine if that is a actual value or calculated?

You are seeing actual oil temperature on the CAN bus . Hopefully the sensor is ok. Another poster is seeing 300F oil temperature off the CAN bus and suspects the sensor has failed. http://www.planet-9.com/987-cayman-boxster-competition/99935-external-oil-coolers.html Rob

I recorded oil temps during my test and found that they closely followed coolant, which made sense given the oil-to-water cooler. Of course car was stationary so I'm not sure how well my values would correlate to normal values mentioned above. Standard Durametric can also display sensors' voltages along with the ecu 's calculated temperatures. I suspect the oil cooler is in the coolant loop with the heater core to help with rapid warm-up, etc. Hopefully someone who knows how this is actually plumbed will post those details.

My 981 water temp is also constant at 194. Oil temp on a long drive last month reached 231. Did not have sport button activated, which I have been told will lower the oil temp.

Yes, the Sport button does lower the oil temp. On similar drive (time of day, same route) I see 6-8 degrees cooler with Sport button on vs. turned off. In fact, today on that drive, I did not engage Sport and noticed my oil temp was higher than what I usually see and immediately punched it on and saw it start to drop.

Thanks. Will give that a try this Saturday when I go on a long drive with the local club. Outside temp is expected to be in the high 90s, so should be a good test.

Ron, Drove over 250 miles this past Saturday. Outside temp was near 100. With Sport mode engaged at 80 mph, I saw oil temp of 205 and water temp at 194.

Sounds very similar to what I experience in Florida at that temp and speed.

BTW, I just ordered a GTS . Will my ScanGaugeII plug in to the OBDCII? In other words, does the 981 / GTS have an OBDCII outlet to plug in to? (I realize this might seem a silly question but all my cars have been pre-CANbus.) Sent from my iPad using Tapatalk HD

Phil, I think it should have the OBD2 connector. The GTS will display all the values we craved in our 987s....What will become of your 987? Regards, Rob

i've driven at the Nurburgring 981 Cayman S and it had OBD2 socket.

Old thread but wanted to share some water temp data after installing a ScanGauge II in my 06 CS on a recent hot day. Normal driving on flat road going 50-70 mph, nominal water temp per the ScanGauge was 190-205 with the AC on and 95F outside temp. Dash gauge steady as usual at 175. Climbing several thousand ft up a mountain with AC on for 20-25 minutes, the ScanGauge temp climbed to 230+. Dash gauge started moving above 175 mark when ScanGauge got to 225 and stopped just before next mark above 175. At 235, I shut off the AC and temp slowly came down to around 220 (dash gauge came back to 175 when ScanGauge was 220). So our idiot dash gauge does move above the 175 mark when you hit 225+ (actual temp).

Good to know. Thanks.