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Old 09-28-2015, 02:02 PM   #1
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Temperature behavior

I'm not sure if this is consistent with other boxsters, but it seems not right:

1) Low speed fans and high speed fans work. Lows on @ 212 according to OBD2 information, needle at right edge of '0'. High speed fans on ~217.

2) with AC on, low speed fans are immediately triggered and will stay on. When the temperature rises about 212 even with the low speed fans operating (100 degrees, uphill climb), I would expect the high speed fans to activate at 217 like normal however I have not seen this behavior. Temps will climb to 223 or so and at that point I just turn off AC, with low speed fans still going but not high speed fans.

3) high speed fans will activate if the low speed fans are already on and I activate AC.

Intermittent coolant sensor (I don't think so, I am seeing properly fluctuating temperatures in relation with fan and driving activity), or some sort of alternate temperature control mechanism I don't understand??
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Old 09-30-2015, 05:52 AM   #2
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My raby powered boxster gets up to about -180 and stays there no matter what. My stock 996 fluctuates with ambient temps, speed, traffic etc and regularly is over 200. Sitting in traffic in the summer i always think its going to overheat, but it never has. I hate looking at the temp gauge knowing it has to be bad for the engine
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Old 09-30-2015, 06:55 AM   #3
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Are you getting these numbers from OBD or from the cluster gauge?
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Old 09-30-2015, 07:29 AM   #4
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As I understand it, the high speed fans should activate when the AC system pressure is above a certain level OR the temperature is some amount (~217 like I have seen when the AC is off?? not sure).

My experience is that the high speed fans will not, with the AC on, activate at the 217 temperature. The high speed fans have activated with AC on before, but this was what I assume to be because of the AC system pressure, since the temp had been climbing well above the 217 mark. It is not always the case that the high speed fans activate once the temperature passes the 217 mark and this is what I am confused about.
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Old 09-30-2015, 07:42 AM   #5
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My car was running hot (just to the right of zero) and I went through everything to see what was causing it. From sitting in the garage overnight, I turned on the AC and both fans kicked on so I assumed the fans was working fine and I went ahead and replaced the coolant, pump and thermostat. Didn't fix anything. Then with the bumper off, and the car running, the passenger fan would not kick on. But when I turn the AC on, they both kicked in at high speed. I bought the relay thing that goes in the bumper, but have not installed it yet. I'm far from an expert, but on my broken 1997...

Car at operating temp, no AC - driver side fan at low speed
Car at operating temp, AC on - Both fans on at high speed
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Old 09-30-2015, 08:12 AM   #6
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Correct assessment, except that AC on will trigger both fans at low speed operation, which indeed happens on my car (How I know both ballast resistors are operational as well as low speed fan relays).

If the low speed fans were already activated and the AC is turned on, high speed fans are activated. I have also witnessed this behavior and both high speed fans work (eliminating the relays as culprits).

It is the following specific behavior that causes my issue:

slow driving(traffic), AC on, low speed fans operational. Uphill climb, mid-speed operation, low speed fans stay on, temperature rises. Temp rises above the 217 mark and high speed fans will not activate (I expect them to activate here). In a few circumstances, temp will rise to 223+ (via OBD readout) and high speed fans still not active. At that point, I turn off AC and the low speed fan operation will bring the temperatures down. I have in some rare cases, seen the high speed fans activate following the previous situation, but my assumption was that it was due to AC pressure, since the temp was higher than the 217 mark and in other instances, the high speed fans did NOT operate at that temperature.

I expect the high speed fans to kick in whether the AC is on or off, at 217F. Does anyone know if this is true? Is it possible that the high speed fan operation occurs at a higher temperature when the AC is on to help some component of the AC stay cold/equalize pressures???
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