Based on my experience over the years and by observing the coolant temperature it takes considerable driving after a cold start before the engine is hot enough to cause the radiator fans to come on.

It takes stop and go driving, with idling mixed in, before this happens. For instance I can drive 30 freeway miles -- to work -- and only after I have been sitting in a fast food drive in driveway for a few minutes do I see the temperature gage (or the actual temperature) climb to the point that I hear the fans come on.

If the A/C is not on the fans coming on that soon after cold engine start suggests there's a problem with the fan electrical system or possibly (maybe this should have been first) a problem with the coolant temperature gage.

Do you know the coolant temperature at the time the fans come on? As you are aware of I think you can use the A/C display to display the coolant temperature. Or you can get an OBD2 code reader/data viewer and through the OBD2 port read and display coolant temperature in real time.

If you observe the coolant temperature rising to 212F (the temperature at which I have observed the fans come on in my Boxster) after a cold engine start in just a few minutes that's a sign the cooling system is not working properly. I would suspect a T-stat or water pump.

You can if you want check T-stat and water pump operation by starting a cold engine with the car on a lift and carefully (!!!) checking the temperature -- by feel -- of the hoses to/from the water pump housing to confirm that as the coolant in the engine warms up it flows to and from the radiators.

If you observe the fans coming on before the coolant temperature reaches 212F that's a sign the fan electrical system possibly has a problem. (Or the DME fan stage controller system is bad.)

 

Schnell- thx IR therm. will confirm temp. readings.

Macster- thank you for taking the trouble to write that up, stepwise and methodical works well for me. Thermostat seems to open at approp. time, and coolant seems to be circulating thru radiators, based on temp. gauge.

1. Temp slowly climbs to 180 marker, then stops rising for a couple minutes (circulation!),
2. then another slow creep up into the zero (in 180), where it stays for another couple minutes,
3. then I start having fun (2nd gear, 3rd gears runs up into 4-5k rpm),
4. then temp rises to 3/4 mark and fans kick on,
5. and that's how it stays for the rest of the drive (30+ minutes).

I'll perform your tests as the days progress this week.

 

So yeah I'm gonna flush the coolant (dealer) and go from there. Before that I'm gonna measure the pH just for my curiousity.

And clean the radiators, and the other diagnostic/maint stuff. I think the coolant system is working, just not as well as it could be. I think it's a maint issue, not a structural issue.

I'll update the results, that's how I roll.

 

Replace your water pump and thermostat since you're in there. It's not a matter if the pump will fail, just a matter of when. You're overdue.

 

Can someone clue me in to how to check actual engine temp through AC? Is this in the owners manual?

Thanks, Paul

 

Press and hold in the recirculate and the top (arrow up) buttons on the right side of the panel for a few seconds. The left screen will change. Using the + key below that screen, advance so the display reads 6c. Then press the center vent button once. The display will show you your coolant temp.

To revert to the original HVAC settings, just press 'auto'. For the rest of that drive cycle, you can get the temp info again by pressing the recirc and arrow up buttons again, and the temp will appear immediately. You have to repeat the whole process for the next drive cycle.

 

https://rennlist.com/forums/6995148-post43.html

 

Thanx Guys!

 

For reference, HVAC showed my car running at 94c (201f) @ 70mph, 4th gear, 23.8 degrees c (75f) ambient temperature. At 94c, the needle on my dash is vertical. Readings with an IR gun were consistent with the HVAC's indicated temp. My car may run slightly cooler than others, as it has been equipped with 3rd radiator.

 

This weekend I went through rain and sun. Temps from 67-82F. Stopped traffic and on highway. Temps were between 93 - 98C. I got the 98C on hot day. Not in traffic, but on a hot day on back roads driving the kids around with a lot of start/stop. 98C was almost at the far egde of the 0.

Only 2 radiators, but low temp thermostat.

As a question, I have seen some say the low temp thermostat will lower the operating temp, but I just thought it opened sooner, so at operating temp it should be wide open with either thermostat so final operating temp should be the same?

 

I was thinking about the same thing this weekend...there is a lot of misinformation and misunderstanding about the function of a low-temp thermostat. Once the tstat is open, temperature is dependent on heat in (engine) vs. heat out (radiators) - the tstat can't affect this outcome.

The low temp tstat adjusts the floor, rather than the ceiling, of the cooling system, so things do not have to be as hot to engage the full capacity of the cooling system. It has no effect on top end temperature.

 

Check your outside engine temp probe to see if it didn't fall out of place. Only had my car for roughly a month thought it was strange that my rear fan on the motor would be running all the time and for a long time after shutting down. After being stuck on the interstate in bumper to bumper traffic in 100 plus outside temps my engine compartment temp warning light came on when the temp gauge was reading below 200. When I finally made it home decided to investigate why it went off sure enough found the probe laying on the motor. Now my rear fan didn't even turn on after shutting down when I came home today in 90 plus temps.

 

@dgjks- yes the digital engine temp. display stayed on just as you said, bingo there's my new gauge, way cool.

@dgjks, @schnell- good point re: low temp. thermostat, so I can cross that off my list.

Here's some temp. readings and observations from my little test circuit run this morning, mostly suburban housing development, so speeds of 25-45 mph, weather temp. 80 F.

Celsius (F), because I couldn't get the conversion keystrokes to work.

81 (178 F) - center mark on gauge, so that mark is accurate.
91 (195 F) - 1st stop (pause) in rising process, paused here a few minutes.
101 (214 F) - middle of zero in 180.
108 (226 F) - fans kicked on (all 3), temp. stayed here idling, end of test.
110 (230 F) - max temp. driving around town recent weeks. Just left of 3/4 tick mark, which I thought was supposed to be 50-percent between 180 and 250, which would be 215, so seems a discrepancy there. Also makes me think if 3/4 tick is 230 (F), then 250 tick might be 280+ which would not be good.
Conclusion - current 230 (F) max temp. not too bad right? and I'll be improving that in coming weeks.

 

Don't be so quick to discount the low temperature thermostat.

http://911uk.com/viewtopic.php?t=94337

 

A low-temp t-stat may still be worth installing, since it starts the coolant flowing through the radiators at a lower temp. On many cars, the low-temp thermostat can be more of a hindrance than a help, since it prevents the engine from reaching operating temp as designed by the manufacturer. For the M96 that (apparently) has some hot spots due to how the coolant flows through the block, starting the flow of coolant to the radiators may help prevent localized hotspots. To my knowledge there is little empirical data (localized temperature readings, thermographic imagery) that definitively proves that the M96 should always run a low-temp tstat, but there are plenty of reputable (in my opinion) resources indicating the use of one on the 996 may be a good idea.

If your thermostat is not functioning properly, it can definitely lead to the car running hotter than it should. If this is the case, a new thermostat, regardless of whether it's a low-temp thermostat or the OEM thermostat, is advisable. However, much of the Interweb's reasoning for running a low-temp thermostat is hopelessly flawed, which is what posts 25 and 26 in this thread address.