cooling fans

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TizzyD
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Re: cooling fans

Post by TizzyD »

Slightly off topic but I'm looking at new fan switches and for the TZD it's saying the two stage fan switch temps are 93-88/97-92°C but I've found one for a n/a 1.7D with a two stage temp setting of 84-79/88-83°C.

My question is, would fitting the lower temp switch have any adverse affects on the system since low speed fans would come on at 84°C not 93°C and turn off at 79°C and high speed at 88°C instead of 97°C and turn off at 83°C ?
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Re: cooling fans

Post by Kitch »

TizzyD wrote:Slightly off topic but I'm looking at new fan switches and for the TZD it's saying the two stage fan switch temps are 93-88/97-92°C but I've found one for a n/a 1.7D with a two stage temp setting of 84-79/88-83°C.

My question is, would fitting the lower temp switch have any adverse affects on the system since low speed fans would come on at 84°C not 93°C and turn off at 79°C and high speed at 88°C instead of 97°C and turn off at 83°C ?


Potentially, yeah, as the fans might stay on while the car's on the move, which means eventually the thermostat will start to close off again. Depends how hot it normally runs I suppose, but there's not normally much benefit in dicking around with fan settings when they work perfectly well standard.
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TizzyD
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Re: cooling fans

Post by TizzyD »

Kitch wrote:Potentially, yeah, as the fans might stay on while the car's on the move, which means eventually the thermostat will start to close off again. Depends how hot it normally runs I suppose, but there's not normally much benefit in dicking around with fan settings when they work perfectly well standard.


Ah ok, that's fair enough. Will see if I can find some markings on the one currently fitted to get a match and replace like for like.
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Re: cooling fans

Post by assembled »

Fan switches are mounted on the cool side of the radiator and will only activate when return temperature reaches preset temperature. I personally would go for lower temperature to have higher safety margin. I don't think fans will stay on when car is moving fast enough or activate at all as TD radiator is so large, but will keep return slightly cooler when stuck in slow moving or standing traffic. Engine outlet temperature is governed by thermostat and if it is working properly you can't overcool the engine with fans.

On my TZD I have also fitted lowest temperature switches that i could find so that dashboard would indicate problem as early as possible and temperature gauge from GTi. I was also thinking of adding a circuit to blink temperature warning light when fans are on. This way if it starts to blink - fans are on, if it starts lights up constantly - engine is overheating, but fans are not activated. But I am a little paranoid of overheating...
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Re: cooling fans

Post by Way2go »

assembled wrote: Sat Jun 10, 2017 9:03 am Fan switches are mounted on the cool side of the radiator and will only activate when return temperature reaches preset temperature. I personally would go for lower temperature to have higher safety margin. I don't think fans will stay on when car is moving fast enough


An internal combustion engine has a design operating temperature range which caters for parameters over and above cooling & concerned with fuel efficiency and engine wear. To tinker with this design range is counter productive.

However, for those concerned with overheating, the likely cause is often the small waterways in the head become restricted. This can be effectively sorted by using "Barrs Professional Flush" (other products are available :) ) which will open these passageways back up and eliminate the odd "red light" ocurrences in stationary and slow moving traffic. Probably a good habit to use this each time before the periodic renewing of the anti-freeze/coolant. However if any redlight occurences are seen, use it then without waiting for the routine interval to save any further degradation and potential damage.
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Re: cooling fans

Post by assembled »

Way2go wrote: Sat Jun 10, 2017 7:44 pm
assembled wrote: Sat Jun 10, 2017 9:03 am Fan switches are mounted on the cool side of the radiator and will only activate when return temperature reaches preset temperature. I personally would go for lower temperature to have higher safety margin. I don't think fans will stay on when car is moving fast enough


An internal combustion engine has a design operating temperature range which caters for parameters over and above cooling & concerned with fuel efficiency and engine wear. To tinker with this design range is counter productive.

However, for those concerned with overheating, the likely cause is often the small waterways in the head become restricted. This can be effectively sorted by using "Barrs Professional Flush" (other products are available :) ) which will open these passageways back up and eliminate the odd "red light" ocurrences in stationary and slow moving traffic. Probably a good habit to use this each time before the periodic renewing of the anti-freeze/coolant. However if any redlight occurences are seen, use it then without waiting for the routine interval to save any further degradation and potential damage.

I completely agree with your first paragraph. Thermostat is responsible for thermal control. Changing cooling fan behavior does not significantly affect thermal operation, only provides cooler coolant. Just think how drastically different cooling is when cruising at below freezing temperatures and being stuck in traffic jam on a hot summer day.
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