Kenlow Sensor Position

[rushdriver]

I have a Dax Rush and it has a Kenlow fan on the radiator. The question is should the sensor for the fan be in the input pipe of the rad ( i.e from the engine) or on the output pipe of the rad ( i.e. the "cooler" water going back into the engine). The reason I ask is that it is currently on the input to the rad but I think that it should be on the output, so when the water comes out of the rad and it's hot because it is not getting any air through it then the fan should come on.

Any ideas??

Cheers

John

[suparuss]

i think the fan should come on relating to the temp of the coolant in the engine rather than in the rad, since its cooler after the rad it may only come on when its too hot coming out of the engine, so id put the sensor before the rad. on my v twin the sensor is in the stat housing bfore the rad.

Russ.

[GreenV8S]

If you have an adjustable switch that can go down to about 70 degrees, put it in the bottom hose. The bottom hose temperatures rise when there isn't enough air flow through the rad, which is when you want the fans to come in. The top hose temperatures rise when the engine gets hotter, which only happens after a big delay and then takes an age to go off again. It works after a fashion but bottom hose is the right answer. But bottom hose temperatures will be 5-10 degrees lower than top hose, so you need a lower temperature otter or an adjustable otter than has a low enough range.

[rushdriver]

That's what I thought about the bottom hose. I can adjust it down to "very" cool so I will set it to 70 degrees and see what happens. I am hoping that it will stop the fan running for ages whilst I drive along the road.

Thanks for your help

John

[Avocet]

Traditionally, all cars have had them in the top hose (the outlet from the engine). I think that if the water that is coming out of the engine is getting close to boiling, you will want the fans to start cooling it ASAP. If you get a sudden rise in temperature, you might find that the water in the cylinder head is starting to boil by the time the water in the outlet hose is hot enough to trip the switch. You could set the switch to a very low value to avoid this but then most of the time the fan will be running when it doesn't need to. Also, the most efficient use of the fan will be to pull the temperature down from (say) 95 degrees to 85 degrees. It will run a lot longer trying to pull it down from 85 degrees to (say) 75 degrees because the ambient air flowing over the radiator core will still be the same temperature no matter what. (As a daft example to make a point, if the ambient air is 20 degrees, you could have the fan running all day and you won't get the coolant below that - even if the engine doesn't dump any heat at all into the cooling system).

[GreenV8S]

The time for the water to flow through the rad isn't the problem. The point of the otter switch is to bring in the fans when the car isn't moving fast enough to produce enough ram air flow. The bottom hose temperature is a very good indication of whether there is enough air flow. The top hose temperature is a very bad indication because you get no signal until the whole engine temperature has changed, which will happen eventually but in the mean time you sit in traffic for five minutes with no fans, and then they stay on pointlessly when you're doing 70 mph.

Edited to add that many modern cars have these switches built in to the bottom tank of the radiator nowadays.

>> Edited by GreenV8S on Monday 2nd June 00:25

[rushdriver]

I must admit to me it makes more sense to put the sensor on the bottom hose and set the thermostat to a relatively low temperature. It's because when the car gets hot and I am driving along the road the fan is coming on and staying on when the water actually going into the engine has been sufficiently cooled by my twin core ali rad.

Any more ideas?


Cheers

John

[Kevp]

Checked my instructions. Switch goes in top hose.

[suparuss]

tomayto tomarto?

[rushdriver]

suparuss said: tomayto tomarto?

Maybe it is but I just get fed up with my fan running for ages when I have stopped the car or I am driving a long the road.

Thanks for your help

John

[Avocet]

Why do most mass-produced cars have them in the top hose, anyone?

[GreenV8S]

Avocet said: most mass-produced cars have them in the top hose

Is that true, though?

[annodomini2]

depends on the age of the car, most new ones are driven from the ECU

[Avocet]

Most of the cars I've seen date from the mid 80s to the late 90s and yes, the bulk of them seem to have it in the top hose or near the top hose end of the radiator. I can see what people are saying about the bottom hose temperature being a good indication of radiator efficiency but I'm not sure I subscribe to the theory because there are too many variables involved. If the airflow through the rad and its efficiency are good, the temp in the bottom hose will be low - great but also if the water entering the rad is cold, the bottom hose temperature will be just as low and the fficiency of the radiator will have nothing to do with it.

[rushdriver]

Avocet

But if the water temp entering the radiator was low then the fan would not need to come on, it's only when the air flow through the rad stops and the water temp goes up that the problems start. I am still not sure what to do really.

Cheers

John

[Avocet]

I think the issue is that the water temp (if it does start to rise) will do so in the engine first. Obviously, this is where the heat comes from in the first place. As it rises, it will enter the radiator but could actually be boiling as it does so and the fan sensor wouldn't know about it until the hot water had passed through the radiator and reached the bottom hose. At low engine speeds, when the water pump isn't shifting the stuff quickly, this could take several seconds during which time the water in the head might have started boiling quite seriously. Now I accept that you could just set the fan switch to a very low temperature so that the danger of this happening was kept to a minimum but I think this will result in the fan running for a lot of the time when it doesn't need to.

To tell the truth, I'm not 100% sure which way is right but I think it would be worth doing a quick survey of as many cars as you can get your paws on. I think even the more modern ones with fans controlled by the ECU will still take their inputs from a sensor near the thermostat housing.

[rushdriver]

Avocet

Good call on checking as many cars as possible. It's a bit of a strange one this. I am off to a car show next week so I will post my findings then

Thanks for your help

John

[annodomini2]

The new clio's use just the coolant temperature sensor in the engine, if the cars been stood for more than a certain period of time above a set temperature it turns the fan on.