Fan Temp Switch location
Discussion
Working on a Cobra Kit car at the moment and in the process of swapping the radiator. The car originally had a Rover V8 rad but this has been swapped for an aftermarket alloy one. The Rover unit had a nipple on the top that connected to the expansion tank. The new one does not. It does however have a nipple on the Fan Switch Housing instead, to feed to the expansion tank. The question is where to mount the Fan Temp Switch?
Initially I'd say that the switch needs to be on the rad outlet, so as to measure the temp of the coolant leaving the rad to determine whether the fans require activating. The engine is a Ford Windsor V8 and unless I'm very much mistaken, the water pump draws coolant from the rad, pumps it up through the engine and it enters back into the rad at the top. Which means that the outlet pipe is at the bottom and that is where the Fan Temp Switch should be located. However, that means that the expansion nipple would also be at the bottom, when surely it needs to be at the top?
Any thoughts?
Initially I'd say that the switch needs to be on the rad outlet, so as to measure the temp of the coolant leaving the rad to determine whether the fans require activating. The engine is a Ford Windsor V8 and unless I'm very much mistaken, the water pump draws coolant from the rad, pumps it up through the engine and it enters back into the rad at the top. Which means that the outlet pipe is at the bottom and that is where the Fan Temp Switch should be located. However, that means that the expansion nipple would also be at the bottom, when surely it needs to be at the top?
Any thoughts?
For me fan temp switch should be on the exit of the engine/entrance to the rad.
This way the fan switch is seeing the max temperature of the coolant and the fan is then cooling the entire water system and not just the water held in the rad. It means the fan will stay on for longer periods as opposed to what would happen if you put the temp switch on the exit of the radiator. In a config where you're sensing exit rad temps you'll get erratic fan activation (i.e. a lot of on/off/on etc.) as once the fan cuts in it cools the water in the rad, sensor see's cool water and turns fan off, until the next lot of hot water comes through and repeat process.
This way the fan switch is seeing the max temperature of the coolant and the fan is then cooling the entire water system and not just the water held in the rad. It means the fan will stay on for longer periods as opposed to what would happen if you put the temp switch on the exit of the radiator. In a config where you're sensing exit rad temps you'll get erratic fan activation (i.e. a lot of on/off/on etc.) as once the fan cuts in it cools the water in the rad, sensor see's cool water and turns fan off, until the next lot of hot water comes through and repeat process.
Edited by NotNormal on Wednesday 11th May 12:10
I have considered this (there are only 2 options after all 
)
I was thinking though having it pre-rad is ignoring the cooling ability of the rad itself. The coolant is always going to be hot coming out of the engine and it may well be that the rad is doing a perfectly good job of cooling by itself. But the fans are still going to be triggered. Basically you want to know that the rad is doing it's job and if not, the fans need to come on? But then I guess as you are saying, you are only introducing additional cooling after it's being metered. I guess it just coming down to how often and what duration the fans come on.
Any suggestions as to the location of the expansion exit, as I think that will be the determining factor?
)I was thinking though having it pre-rad is ignoring the cooling ability of the rad itself. The coolant is always going to be hot coming out of the engine and it may well be that the rad is doing a perfectly good job of cooling by itself. But the fans are still going to be triggered. Basically you want to know that the rad is doing it's job and if not, the fans need to come on? But then I guess as you are saying, you are only introducing additional cooling after it's being metered. I guess it just coming down to how often and what duration the fans come on.
Any suggestions as to the location of the expansion exit, as I think that will be the determining factor?
TEKNOPUG said:
I have considered this (there are only 2 options after all )
I was thinking though having it pre-rad is ignoring the cooling ability of the rad itself. The coolant is always going to be hot coming out of the engine and it may well be that the rad is doing a perfectly good job of cooling by itself. But the fans are still going to be triggered. Basically you want to know that the rad is doing it's job and if not, the fans need to come on? But then I guess as you are saying, you are only introducing additional cooling after it's being metered. I guess it just coming down to how often and what duration the fans come on.
Any suggestions as to the location of the expansion exit, as I think that will be the determining factor?
Don't forget that (in an adequately sized rad for the engine coupled with an appropriate thermostat) the fan should only be coming on when you have minimal airflow through the rad i.e. when at standstill or crawling. So in this scenario the engine shouldn't be producing loads of extra heat as it's not working hard. Therefore you should be getting a more constant temperature coming out the engine as opposed to superheated water from a "worked" engine.)I was thinking though having it pre-rad is ignoring the cooling ability of the rad itself. The coolant is always going to be hot coming out of the engine and it may well be that the rad is doing a perfectly good job of cooling by itself. But the fans are still going to be triggered. Basically you want to know that the rad is doing it's job and if not, the fans need to come on? But then I guess as you are saying, you are only introducing additional cooling after it's being metered. I guess it just coming down to how often and what duration the fans come on.
Any suggestions as to the location of the expansion exit, as I think that will be the determining factor?
In addition, the activation and de-activation temps of the fan switch are not a single temp reading. So fan on for example could be 95deg and fan off would be 92deg so there is a window of heat that the engine would have to re-heat the water from fan going off to fan coming on again.
With regards to the expansion pipe, on my Vauxhall based engines it comes again from the entrance chamber of the rad (exit path of engine).
Fan switch on Kenlowes is fitted at the top of the radiator where the top hose goes into the rad.
Think you'll find most cars - can't think of any exceptions although I'm sure there probably are - the sensor is as high as practically possible as that's where the coolant is likely to be hottest.
Think you'll find most cars - can't think of any exceptions although I'm sure there probably are - the sensor is as high as practically possible as that's where the coolant is likely to be hottest.
E-bmw said:
Every OE one I have seen is in the side of the rad itself.
I think the Kenlowe ones were typically on the inlet hose as that is the easiest place to fit a surface type sensor, the OE ones normally are in contact with the water rather than a hose.
Kenlowe is a bulb fitted in the hose, so in the coolant, not mounted externally on the hose.I think the Kenlowe ones were typically on the inlet hose as that is the easiest place to fit a surface type sensor, the OE ones normally are in contact with the water rather than a hose.
As one Cobranaut to another you need to have the fan switch screwed in a bung welded/ brazed into the end tank of the radiator about 2 inches below the top hose inlet.
I'd get a standard 85 degrees C switch will mean that as long as your fan can move enough air, and the rad is big enough, your car will never overheat.
One thing is that the fan should never, ever be mounted using the plastic mounts that go through the rad fins.
The vibrations from the fan simply cause the ties to saw their way through the rad.
Ask me how I know and why the last two Cobras I built use a proper metal frame from which to suspend the fan whilst the first, the one I replaced the radiator on, used the "through the rad" plastic ties?
hth
Cheers,
Tony
I'd get a standard 85 degrees C switch will mean that as long as your fan can move enough air, and the rad is big enough, your car will never overheat.
One thing is that the fan should never, ever be mounted using the plastic mounts that go through the rad fins.
The vibrations from the fan simply cause the ties to saw their way through the rad.
Ask me how I know and why the last two Cobras I built use a proper metal frame from which to suspend the fan whilst the first, the one I replaced the radiator on, used the "through the rad" plastic ties?
hth
Cheers,
Tony
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