Mark944na86

Hi all,

The thermo fan switch on my S2 has failed, so I need to get a replacement. The standard switches are 92/102 degrees C, but I notice there is a "cooler" version that switches at 82/92 degrees C.

What issues do I have to consider, in choosing one over the other, if any? What's the rationale for selling the "cooler" switches in the first place? Any disadvantages I should know about to having the fans coming on at lower coolant temps?

Thanks for any advice.

-Mark

bearone

both the water pump and switch need to be low temp.

87951

Mark944na86

You mean the thermostat in the waterpump? Why would this have to be lower temp? Once the engine reaches normal running temp, this is always open anyway... the only thing the thermo fan switch would do is to keep the fans running longer over the radiator... so don't understand the reasoning here.

-Mark

Mike C.

If your cooling system is less than optimal, a lower temp switch can cause problems in that the fans may run a lot longer than normal since the low temperature cut off is never reached during operation. This would also keep the fans on longer when the car is shut off.
How do you like it in Brisbane Mark? I've been there several times on business and really enjoyed it.

black944 turbo

I have a low temp. thermostat and switch. As far as I can tell no adverse side effects. It just keeps my car from reaching the third mark.

Dilberto

Wahler and Thomson/Behr make switches that activate the fans at 120*F. Like the others have mentioned- make sure the thermostat matches accordingly. Your car will run cool as a Cucumber.

Zach

CO951

Mark, the reason you need to lower your therostat if you lower you fan switch is that if the fan comes one, but the thermostat isn't open, it doesn't help to cool, because the coolant isn't circulating. I'm thinking of puting in the lower temp thermostat and switch, too.

bearone

yes, my mistake. should be thermostat.

depends on the value of the thermostat as to where the temp will run, and the switch picks up the increase in temp and turns the fans on so both need to be low or hi.

it would seem that if you had a low temp thermostat but hi temp switch, the fans would come on later, at the higher value, which gets you closer to the 3rd line.

87951

PorscheDoc

I also run the lower temp thermostat. Car sits right on the first mark when driving. On really hot days in traffic, it never goes above the 9 o'clock mark.

bearone

that's about the same with mine, both low. cruising, idling, a/c on or off.

87951

hosrom_951

The OEM from Porsche is rated at 91/105C

Cooler versions run in the 80C/91C range

Been using the cooler one on my 951 and NA, i have to since the weather here is hot (it was 114F in the shade today).

AR10

The hotter the engine runs the more efficient it is. Most modern engines run
220f to 240f. As long as the coolant is not boiling and has a good pressure cap, it is not too hot.

hosrom_951

When it comes to water/coolant, i would disagree. The hotter the cooling system is, the harder it is (longer it takes) to cool down.

I don't know where you got the info on where modern engines run 220-240F (104C-115C) is incorrect, since the brand new 06 BMW 323i has the high speed fans kick in at 91C.

Come to think of it, the red zone in the 951/944/968 is 115C (240F).....that's NOT good.

IMB951

WHAT!!! Why use coolant at all then?

AR10

Ceramic engines have been built which use no cooling, or very little. I have run engines to destruction with no coolant and they always run the best right
before they give up. Most American cooling fans are computer controlled to
turn about 240F.