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Old 07-27-2011, 11:11 PM   #1
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Radiator Fans and water temp

I'm posting this here on behalf of a friend who has a 2000 996 C4, I'm assuming that the cooling system will be similar to a 986, hence... posting here.

Suddendly over the last one month, my friends 996's radiator fans has been coming on (low) at 100 degrees C and high at 103 degrees C. Hence, the water temp (at gauge) is alternating between 100 degrees C and slightly below it. Used to be about 90 or so.

So far, since then, he has changed the water pump (original), LN low temp thermostat, flushed the coolant but the characteristic is still unchanged (strange..). He has also taken the bumper off and cleaned the radiators (bagful of leaves, stones etc).

I'd asked him to look at the aircon diagnostic and the only possible clue is that his 1C (oil temp) reading is very low - can be 50 degree C when warmed up and even had a reading of zero. The 6C reading is similar to the water temp gauge - 100.

Is the DME "smart" enough to delay the radiator fan operation as it thinks the oil is not warmed up yet ??? That might explain the problem ?


Last edited by shlim8; 07-27-2011 at 11:17 PM.
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Old 07-27-2011, 11:13 PM   #2
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Another question - would the in-line series resistor cause the operation of the fans to come in late ?? But then, since both fans are coming in late, would have to be a similar failure on both resistors (unlikely ?)
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Old 07-28-2011, 10:43 AM   #3
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1. The dash temp gauge is both inaccurate and non linear (180 is often more like 210F)

2. The temps at which the fans kick in are controlled by the DME software reading the water temp

3. The A/C "hack" display is known to be very inaccurate at best; any relationship between it and the real values are purely coincidental

4. If both fans run at both speeds, there is nothing wrong with the resistors
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Last edited by JFP in PA; 07-28-2011 at 10:47 AM.
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Old 07-31-2011, 10:08 PM   #4
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Thanks for the reply.

But if the temp used to be 90 on the meter and now it's jumped to close to 100, it would seem that something has changed. Regardless of whether the meter is non-linear or not...

Any ideas on whether a failed oil temp sensor would cause the DME to turn on the fans later ?? It would seem the water temp sensor is ok, since both gauge and a/c show a higher water temp of 100. Unless the DME reads the water temp from a different sensor ?

He has to order in an oil temp sensor, so was wondering if there is anything else that might be needed. Out of desparation (me thinks), he's flushing the radiators as well, but I doubt that's going to help, since the fans are coming in at 100 (low) and 103 (high) C and I don't think there are any temp sensors at the radiators.

Another thing he noticed was that the coolant level has actually gone up (when cold). I've never seen that happening... only down not up. Air in the cooling system ?? I had passed him, the burping procedure for tip cars to him, not sure if his mechanic had followed the procedure. But I would presume that after a week, any air should have gone through the system ?

Last edited by shlim8; 07-31-2011 at 10:15 PM.
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Old 07-31-2011, 10:40 PM   #5
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This really sounds like air in the cooling system, but the 996 expansion bottle is different to the Boxster one, and I'm not sure if there is a bleed valve you can leave open for a couple of heat cycles to rid the system of air like you can on the Boxster.
Have a look at Rennlist.com (under 996 Forum) and use the search function - it may help with diagnosing the problem....
As a matter of interest, did your friend split the radiators (coolant and A/C) on both sides when he removed the bumper and removed the rubbish - mine looked reasonably clean untill I split the rads, then a load of leaves, grass, cig butts etc fell out and even more when I hosed out between the rad fins.
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Old 08-01-2011, 12:28 AM   #6
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Yes, most of the rubbish was between the condensor and radiator.

Hmmm, I guess there will be another round of burping again, since the car will in for radiator flushing again. He suspects choked radiators although I doubt it's going to help.
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Old 08-01-2011, 11:06 AM   #7
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I have to agree with Steve; if the cooling system is not being refilled with a vacuum system, it has air in it. And it does have a bleeder very similar to the Boxster.

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