Radiator Fans Questions

[Tom163]

Hi all,

I want to check my fans are working on both high and low speeds but there is so much contradictory information on the internet thought i'd best ask.

When I hit the A/C button when the engine is cold or hot are the radiator fans meant to come on the loud or quiet mode?

I was going to test each fan mode by removing 1 resistor at a time and bridging two pins with some wire, does the car have to be in any special state for this test? like warmed up engine? a/c turned on etc? or will they come on no matter what soon as they are bridged?

 

Thanks in advance.

[witko999]

When you turn the aircon on the fans should come on at low speed.  High speed should only come on (I believe) when the engine temperature requires it.

If the fans only work at high speed then your fan resistors need replacing.

The car doesn't need to be in any special state to do your test.  I did the same and one of my fans didn't run at low speed so I replaced the resistor on that side.  Be careful, when you bridge the relay for the high speed, your wire will get hot immediately.

[edc]

The ac compressor will only work above a certain temperature. So assuming you test it while the weather is still warm it should work as normal.

[Tom163]

7 hours ago, witko999 said:

When you turn the aircon on the fans should come on at low speed.  High speed should only come on (I believe) when the engine temperature requires it.

If the fans only work at high speed then your fan resistors need replacing.

The car doesn't need to be in any special state to do your test.  I did the same and one of my fans didn't run at low speed so I replaced the resistor on that side.  Be careful, when you bridge the relay for the high speed, your wire will get hot immediately.

Thank you for that Witko...especially the wire heating up tip lol.

5 hours ago, edc said:

The ac compressor will only work above a certain temperature. So assuming you test it while the weather is still warm it should work as normal.

Thank you edc!

[Richard Hamilton]

Switch-on conditions for coolant or condenser blower motors:

 

Stage 1 is switched on when the coolant temperature is >100°C

or

there is an A/C demand, the intake air temperature is >8°C and terminal 15 (ignition) is switched on.

 

Stage 2 is switched on when the coolant temperature is >105°C

or

the refrigerant pressure is >16 bar.

[Tom163]

45 minutes ago, Richard Hamilton said:

Switch-on conditions for coolant or condenser blower motors:

 

Stage 1 is switched on when the coolant temperature is >100°C

or

there is an A/C demand, the intake air temperature is >8°C and terminal 15 (ignition) is switched on.

 

Stage 2 is switched on when the coolant temperature is >105°C

or

the refrigerant pressure is >16 bar.

Thanks Richard. Thinking about it at the minute my aircon doesn't have any refrigerant in it and needs re-gassing, I am guessing mine in this state will be under the 16 bar pressure?

[edc]

If the AC system is dead the compressor won't kick in anyway so won't force the fans on. 

[witko999]

Yes but you can still bridge the relays to see if the fans will work correctly.

[Anker BS]

An easier way it to start the car with the AC on and let it come up to temperature while standing still. When the temperature needle climbs to the next stop above the normal "over the 8 in 180" the high speed fans should turn on. The difference in noise if very noticeable.

[Tom163]

Hi guys,

The AC system works in my car its just out of gas/refrigerant that makes it cool at the minute, this morning when the engine was cold I hit the AC button and I could hear the compressor kick in and the interior fans get a bit faster/stronger. I could hear the fans come on at the front of the car both sides but I think they are coming on at high speed straight away due to me being able to hear and feel them both. 

I have been told when they are on low speeds they are hard to hear with the engine running. 

[ooid]

If you do not have A.C. that's also hard to diagnose. Here is how I figured it out;

Stage 1 Fans - They should operate when the needle hits just right side of the "0" of "80"

Stage 2 Fans - If stage 1 does not work, and the engine got quite high, the stage 2 should start running just before the middle between 80-120 (like the image below). And yes, they are quite loud!

Now, as it's been documented quite a lot, these resistors fail quite early. So what I found, especially the cars that being exposed to slow urban traffic, daily use, the engine usually operates on quite high temperature. As we all know, both 996 and 986 have massive coolant capacity, so when you have loads of hot water going around engine, in longer time, the engine parts ages prematurely. (I think this showed in thelike earlier models, having D chunk failure, cracked cylinder heads and so on...)

I have realized this issue, after rebuilding my 986 engine about two years ago. Most specialist also aware of this, as this is partly called "Cooling inefficiency" of 986/996 engines. Ideally, with a good specialist, you can get good resistors, store them properly on where they are located, good radiators, LTT and finally the ECU can be hacked, making sure that stage 1 fans operate much earlier than usual time. With this hack, the engine will have a very good life-span and the car should not suffer from over-heating. 

It is already difficult to cool a mid-engine flat 6 when your radiators in the front, so ideally a bit of tweaking is a must imho.

[PaulQ]

45 minutes ago, ooid said:

It is already difficult to cool a mid-engine flat 6 when your radiators in the front, so ideally a bit of tweaking is a must imho.

Do you know whats different about the later engines as they all have pretty similar coolant operating temperatures to the 986 as far as i'm aware ?

 

[ooid]

1 hour ago, PaulQ said:

Do you know whats different about the later engines as they all have pretty similar coolant operating temperatures to the 986 as far as i'm aware ?

 

In terms of the fans, I believe 987.2 have different software set-up for the fans kicking in. I know from colleague (987.2) fans would stay longer even after the engine shuts off for a while, to maintain good balance. Anyone with a 987.2 would have a much more solid opinion I guess. On 981, you also have start/stop so that really helps as well on congestion.

In addition to the cooling fan control with software, 987.2 engine (9a1) has loads of interesting upgrades. Water pump is closed impeller, and engine deck is closed. The closed deck creates more oil and water temp but it is in general much better setup to maintain stability. Also, If I remember correctly, 9A1 engine has a better coolant flow design + head gasket is a multi layer component. When you compare all little changes, thermal heat transfer is much more efficient.

I've never heard any 987.2 or 981 owners having problems with cooling, they have been around more than 10 years now and that really tells us something  

[PaulQ]

9 minutes ago, ooid said:

In terms of the fans, I believe 987.2 have different software set-up for the fans kicking in. I know from colleague (987.2) fans would stay longer even after the engine shuts off for a while, to maintain good balance. Anyone with a 987.2 would have a much more solid opinion I guess. On 981, you also have start/stop so that really helps as well on congestion.

In addition to the cooling fan control with software, 987.2 engine (9a1) has loads of interesting upgrades. Water pump is closed impeller, and engine deck is closed. The closed deck creates more oil and water temp but it is in general much better setup to maintain stability. Also, If I remember correctly, 9A1 engine has a better coolant flow design + head gasket is a multi layer component. When you compare all little changes, thermal heat transfer is much more efficient.

I've never heard any 987.2 or 981 owners having problems with cooling, they have been around more than 10 years now and that really tells us something  

You have made me think a bit to be honest as my car as I expect thousands of others has had busted fan resistors for years. I have made up some new ones though, which I will be fitting soon.

In the summer months, and/or in slow moving traffic my car will quite happily sit at 100 deg+ and the fans will cycle on & off. Never really thought of it as a problem though as it doesn't overheat.

[edc]

When 986 were just conk g out of warranty and up to 7 years old or so I bet there weren't that many proportionately with cooling problems. Crud on the rads hasn't yet killed them and items like coolant cap and tank hadn't degraded. You may see these come as problems for the newer cars in 5 years or you may not. Either way, it's not a huge worry as you simply have to be mindful and understand what the failures are and under what conditions they may happen and act accordingly. It's not like the UK is a hot climate and there are plenty of Boxsters running in much tougher conditions. 

[PaulQ]

As far as I know, my cooling system is operating ok.

Rads are clean and leak free, water pump/stat/coolant & expansion tank have all been replaced in the last 20k or so.

Being an early car the climate hack works on mine, so i've pretty much always got it set to read out the coolant temperature.

Even when I replace the resistors the temperature is still going to be over 100 deg c before the fans kick in.

I guess the way to look at it is the car has made it to nearly 140k over the last 20 years

 

 

[Tom163]

Thanks all for the information here its a big help....soon as I get a dry weekend I am going to do some digging