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augidog · Joined: 03 Mar 2003 Posts: 1360 Location: New Jersey

Someone please explain how these 2 work together if they are rated at the same temp.I am updateing to a 2 fan system and want to buy the 82c lower temp switch. Does the thermostat have to follow and why?
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1978 924 95 mile daily driver.
Audi TB/POR174M/High Flow Cat/2.25" exhaust
I knew that positive thinking thing wouldn't work.

leadfoot · Posted: Fri Sep 15, 2006 11:34 am Post subject:

Thermostat controls the flow of coolant from the engine to the radiator and back to the engine... It also regulates the idle temperature to a certain degree due to how open it is at what temp... (this also relies on the given size of a radiator and airflow to it)

The thermo switch control the temp at which the fan kicks in... to aid in cooling... This it regulates how quickly the radiator can cool back to the idle temperature when the coolant runs hot at hard driving....
e.g.
If you find that under drivng conditions your car runs really hot (in the red under medium driving) and the fan is working overtime then a lower temp thermostat will aid by giving more flow, the result will be your fan will tend to kick in only when it needs to at hot temps. Now this will be noticable and your coolant temps should stabilise at medium/hard driving and drop quickly at idle.
Gauging when your fan kicks is subject to where you want your car to stabilise at during medium to hard driving, as this is when the fan starts to operate (think of it like a recovery zone)... if your temps tend to rise really quickly to red zone from light to medium driving and then stabilise in the red, then this is a prime candidate for a lower temp switch. you want it to stabilize earlier.
now IIRC the zones on the coolant gauge go from cold through three lines and then end up in red zone, and these are acutally represented by the temps 80,85,90 Celcius : it's probably in F but that's what I worked out as a rough guide for my car. So if your car at idle stabilizes around the half way mark then this is good, and if under hard driving it stay under the red or just in then this is ok too, and lastly if the fan is kicking in and out at idle this is good you don't want it operating all the time at idle...
hope my novel made sense...
Leadfoot
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1981 ROW 924 Turbo -
carbon fiber GT mish mash
LS1 conversion in progress...

Chrenan · Joined: 15 Jan 2003 Posts: 3903 Location: Canada

I've got a lower temp therm and switch and my heat sits at the first quarter mark, never above.
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1987 951 - M193 Version for Japan

leadfoot · Posted: Fri Sep 15, 2006 2:36 pm Post subject:

I remember Eric saying the same thing about his car too... I try to run the coolant at 85 it may be a case of the markings being 85/90/95 C which would put your car spot on... I monitor off my ECU for coolant temps and have the fan coming on around 83/85, I bypassed the resistor and ran it straight through a relay so it sucks about 30% more air so I have it coming on a little later...
Leadfoot
_________________
1981 ROW 924 Turbo -
carbon fiber GT mish mash
LS1 conversion in progress...

augidog · Joined: 03 Mar 2003 Posts: 1360 Location: New Jersey

Leadfoot,
Well said TY- This is why this forum is great. Now I get it.
Its nice to know why and how.
_________________
1978 924 95 mile daily driver.
Audi TB/POR174M/High Flow Cat/2.25" exhaust
I knew that positive thinking thing wouldn't work.

D Hook · Joined: 02 Nov 2002 Posts: 3158 Location: Omaha, NE

leadfoot · Posted: Sat Sep 16, 2006 3:31 pm Post subject:

Just checked the temperature marks they are 85/90/95 Celcius for the quarter, centre, three quarter mark respectively...
Leadfoot
_________________
1981 ROW 924 Turbo -
carbon fiber GT mish mash
LS1 conversion in progress...