Best temperature range switch for electric fan?

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Flossie

Flossie

Well-Known Member
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Location
Shropshire
I've got one of those alloy inline coolent doo dahs that have a thermo switch to put the radiator fan on when it's getting too hot. The switch that came with it is busted and there are no markings on it to indicate it's range so I'm after a new one.
My question is what temp would I need the fan to come on at?
Disco 200 TDI in a 110.
I've established the thread size and found a selection in that size on fleabay just don't know which temp range to choose.
TIA.
 
A bit below 84c is the figure I have in my mind for some reason?

I think that's what the engine thermostat (the mechanical one) is set to, so probably a bit lower than that would be good.

The stat got knocked on my 101 once... I keep meaning to replace it with an electronic setup with a readout and a light to show that the fan is running.

How do you have the sensor mounted?
 
It's like an inline "tee" you cut the rad hose and fit it between. Sensor screws into the "tee". Mines fitted in the bottom hose which was considered best practice at the time. The sensor switches a relay for the fan and I have an override switch in the cab.
 
Last one I did was set at 95 coming out the bottom of radiator, stat opens at 86°~88° which is operating temp, beyond 95° is hot so I set it there and never had problems, also depends on accuracy of gauges, D2 seems to read hot only once terminal damage has been done :(
 
I have an 88deg stat fitted.
Bearing in mind this thermo switch is fitted in the bottom hose, so the coolent will have been cooled down from the radiator, I have 3 temperature ranges available to me, these are-
Fan on . Fan off
82. - 72
88 . - 79
95 . - 86

Thoughts gents..
 
95-86
I rarely have my fan on except when it gets near the 3/4 off roading
Cools quick & lets the thermostat do its job

Why in the bottom hose?
 
It was considered best practice at the time by the supplier 10 yrs+ ago.
Pros and cons for both top and bottom hose fitment but bottom made sense to me.
Agreed, mine only come on when Laning in low range really.
 
Flossie said:
It was considered best practice at the time by the supplier 10 yrs+ ago.
Pros and cons for both top and bottom hose fitment but bottom made sense to me.
Agreed, mine only come on when Laning in low range really.
Click to expand...

The main idea behind bottom hose fitting is that the coolant has passed through the radiator and only needs cooling if it exceeds a certain temperature, no point it switching on when the coolant hits 95 degrees out of the engine in the top hose when it is exiting the radiator at less than 82 degrees so the determining factor is the heat being drawn off through the radiator.
 
dieseldog69 said:
The main idea behind bottom hose fitting is that the coolant has passed through the radiator and only needs cooling if it exceeds a certain temperature, no point it switching on when the coolant hits 95 degrees out of the engine in the top hose when it is exiting the radiator at less than 82 degrees so the determining factor is the heat being drawn off through the radiator.
Click to expand...
The main idea if the normal running temperature of the coolant is going above then the fan switches on and cools the coolant as if passes through the radiator, hen the temp sensor is fitted to the top hose.
That is probably why Kenlow suggestion the top hose for the temp sensor in their installation guide, and then to set the supplied variable temp switch to a few degrees above the normal running temperature, if not the fan would be on permanently once the engine is up to temp.
 
discool said:
The main idea if the normal running temperature of the coolant is going above then the fan switches on and cools the coolant as if passes through the radiator, hen the temp sensor is fitted to the top hose.
That is probably why Kenlow suggestion the top hose for the temp sensor in their installation guide, and then to set the supplied variable temp switch to a few degrees above the normal running temperature, if not the fan would be on permanently once the engine is up to temp.
Click to expand...
Kenlowe might have done, but then again I didn't buy their kit, I opted for the X-engineering kit that specified fitting in the bottom hose for the exact reason I gave.
 
Perhaps is a good idea to state the kit being fitted, as we know using an x engineering temp sensor isn’t as precise as the adjustable item such as the Kenlowe item, this is why x engineering’s suggestion for fitting theirs to the bottom hose is the place it should be.
Therefore there’s options in the placement of the temp sensor, and not fixed.
 
dieseldog69 said:
Kenlowe might have done, but then again I didn't buy their kit, I opted for the X-engineering kit that specified fitting in the bottom hose for the exact reason I gave.
Click to expand...
IdI forgotten where I got mine from and your post has jogged my memory, x-eng is mine also.
I think their switch's are poop though, one was faulty out the box and the other two , the terminals dropped off so I'm looking for a different supplier.
 
Flossie said:
IdI forgotten where I got mine from and your post has jogged my memory, x-eng is mine also.
I think their switch's are poop though, one was faulty out the box and the other two , the terminals dropped off so I'm looking for a different supplier.
Click to expand...

Take the housing down to your local motor factors and get one that fits the hole that runs the temp you want, Foundry 4X4 have replacements https://foundry4x4.co.uk/index.php?route=product/product&path=65_1760&product_id=271
 
It's the foundry ones that I've had trouble with .
Finding a supplier is easy enough now I know the thread size (M22x1.5) , would like to get a branded one except motoquip (?),
They seemed the worse.
 
The Mad Hat Man said:
fitting in bottom hose is only an indication of cooling efficiency. does nothing to stop overheating.

think about why a fan is fitted.
Click to expand...

Yes but you only need the fan to come on when the radiator can no longer cope with low air volumes passing through.

Mechanically driven fixed blade fans were easy, fast and cheap back in the day, upgrade to the most reliable form of cooling was the viscous coupling that locked the fan once it reached a certain temperature, a knock on side effect that was a bonus for turbo intercooled engines was mechanically driven fans helped with intercooler temps when running at slow speeds as air was continuously being drawn through the intercooler.
 
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