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Old 08-20-2015, 07:54 AM   #1
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radiator fans ?

Trying to understand how the cooling fans cycle . this pertains to my 996 3.4 which i believe the cooling system operates the same as in the 986 . it has been hot up here in the northeast lately and sitting in slower traffic my temp. climbs to the right side of the zero in the 180 mark . my fans cycle but on low only and the needle barely moves from that point until i am under a steady speed again . my fans never cycle into high . I turn on my AC and the fans come on in high mode and they quickly push the temp down . Is this normal ? should the fans cycle into high on there own ? my boxster needle barely moves in this kind of traffic .

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Old 08-20-2015, 10:16 AM   #2
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This is completely normal - the low speed fans keep the temperature from continually climbing when passive air cooling through the radiators is not adequate. the fans will switch to high speed when the low fans are not able to keep the temperatures down. In traffic low speed fans are fine. With AC in ~95F traffic, low speed fans are also normally adequate. High fans come on under a variety of circumstances, but as long as you can hear them coming on at any point, then you know they work, so ideally they will come on when required.
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Old 08-20-2015, 11:12 AM   #3
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jacabean, what model year is your 996?

My boxster's cooling system works just like yours and my needle even goes to the right side of the 0 in 180 in 100+ degree heat in standing traffic. Some of the needle position has to do with how it was put on the gauge in the first place... the needles in our gauges are not pinpoint accurate.
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Old 08-20-2015, 11:31 AM   #4
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If you are curious and want to compare against some real data, plug in an OBD2 adapter and watch the temp numbers. Lots of members have good data to compare and see if things are operating normally.
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Old 08-20-2015, 02:57 PM   #5
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My 996 is an 01 3.4 . I love this car and it handles great with the PSS9s and GT3 bars . I think it handles much better than my boxster S with the ROW MO30 in the tight stuff.

Most of the info i got is that the temp swings are normal and that the early 3.4 motors tend to run a little hotter than other M96 variants. still a little concerned about how it just shoots up . In The winter time It take forever just to get the car up to temp.





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jacabean, what model year is your 996?

My boxster's cooling system works just like yours and my needle even goes to the right side of the 0 in 180 in 100+ degree heat in standing traffic. Some of the needle position has to do with how it was put on the gauge in the first place... the needles in our gauges are not pinpoint accurate.

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Old 08-20-2015, 11:34 PM   #6
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When the A/C is on, the low speed fans run continuously.

When the A/C is off, the low speed fans start running at a certain coolant temperature. They may be enough to keep the coolant temperature from rising much further depending on outside temperature and speed.

If they don't, then the high speed fans will start running at a somewhat higher coolant temperature, Another forum member or a search may say what those trigger temperatures are.

Last edited by thom4782; 08-22-2015 at 07:45 AM.
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Old 08-21-2015, 07:49 AM   #7
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Here is a thread on installing a switch to manually control the fan. Thread 2 spells it out well. I would do it, but I need pictures to see exactly where these wires are.

Manual radiator fan
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Old 08-21-2015, 09:09 AM   #8
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Quote:
Originally Posted by thom4782 View Post
When the A/C is on, the low speed fans run continuously.

When the A/C is off, the low speed fans start running at a certain coolant temperature. They may be enough to jeep the coolant temperature from raising much further depending on outside temperature and speed.

If they don't, then the high speed fans will start running at a somewhat higher coolant temperature, Another forum member or a search may say what those trigger temperatures are.
I have an issue with my right side fan not running at low speed. This results in in a +5 to +10 coolant temperature. When I turn the A/C on, both fans function and the temp drops to normal. I was under the impression that the A/C turned the fans onto high speed? I have a '97
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Old 08-21-2015, 09:22 AM   #9
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The AC will turn the fans high speed if the coolant is above a certain temperature or if the AC system pressure is above some number, otherwise it will activate the low speed fans.
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Old 08-22-2015, 03:10 AM   #10
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I have a 99 and as soon as I put A/C on the fans operate high speed continuously. I had issues with care running hot and found passenger side fan not working at all and drivers side only on high speed. I found this by removing all 4 fan relay's and by using a "jumper" to test both fans.
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Old 08-22-2015, 04:32 AM   #11
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I noticed I was running a bit warm and decided to test everything to determine the problem. I tested the fans by turning on the AC and both fans worked. Pulled the bumper and cleaned out the radiators (they weren't too bad). I changed the water pump, thermostat, and coolant. And I burped the coolant for an extraordinary amount of time. It was during this time that I got around to the front of the car with the bumper still off and I noticed one of the fans wasn't running. Kicked on the AC and they both kicked on at high speed.

I'm still undecided if I'm mad that I changed everything else or not. It was probably due anyway.
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Old 08-22-2015, 07:47 AM   #12
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When a fan doesn't run at low speed at all, the cause is often a failed ballast resistor on the non-running side.
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Old 08-24-2015, 10:11 AM   #13
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I have come to the conclusion that my system works properly . The system is not ideal for hot weather . no need for manual switches , just turn the AC on and the car cools back down to normal operating temps . It's a shame most people in my region put their cars away for winter . these motors love the cold and seem to make much more power in cold weather . last winter I had my box S on the highway running with an e36 M3 in extreme cold and I was shocked when i saw 138 on the speedo , motor felt so strong . not the same in the hot summer weather .
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Old 08-24-2015, 10:18 AM   #14
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I also found it best to use a power washer when you clean the radiators . My 996 radiators looked clean when I took the bumper off but after closer examination i found that about 40% of the surface area was clogged . compressed air and vacuum cleaning did nothing to clear the compacted dirt out .
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Old 08-24-2015, 11:26 AM   #15
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jacabean, I second your cold weather performance observation and that's a great tip about the power washing. I did take my hose and use a sprayer attachment to blast as much out as I could, but I'm betting I left a lot in there without a power washer. Next time I'll do just that.

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