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[Delk]

My mechanical fan clutch died sometime back so I put my old electric fan back on. The problem or question I have is with the sensor. Mine is located in the engine outlet between the thermostat and radiator. It works fine and but once its on it rarely turns off since the engine outlet temperature is high as it should be.

Does anyone have a sensor on the lower return to engine cooling line? If so what temperature sensor do they have and where did they get it.

My thought is the everything is working fine except the fan should only come on when the radiator is not cooling enough. At the moment the engine outlet temperature is controlled by the thermostat and it will never drop below the level of the fan sensor.

[Uncas]

Why not wire a switch in line so that you can turn the fan off useful for wading

Uncas

[Dave The Sparky]

http://www.x-eng.co.uk/X-Therm.asp?MID=38 

[Dave69]

temp sensor should be located on the radiator inlet hose, that will give a true temperature of the coolant and will operate the fan accordingly to keep the temperature within a safe range (dependant on the cooling spec of the fans)

If you put it in the bottom hose you will then have to know the cooling effect of the rad to set the temp required for the fan to cut in. Car engines have sensors in a manner of places but all have factors applied to take into account their location.

a sensor in the top hose is the easiest to work with

[Delk]

My life has been spent with very large diesels usually above 10,000hp for moving ships around. With big engines you control both the outlet temperature and the inlet since you don't want to overcool the inlet.

The thermostat should always maintain and engine outlet of around 90 degrees. But depending on air flow the radiator will have a different cooling effect so the inlet temperature will be up and down. My thought was if the sensor was on the rad outlet it would turn the fan on when the engine inlet temperature started to rise above a set level. Say 90 degree out and roughly 60 degrees in.

[Jonny Jeep]

My ScangaugeII shows my temp at the thermostat housing to vary typically between 94-104°C. Can your temp sensor/control for the fan be adjusted? Do you know it's on/off temps? Just looked at the fan switches linked above, looks like both of those switches would leave the fans running continuously on a TJ.

Presumably the sensors for electric fans are like other temp sensitive resistors and have an inverse relationship with temp. That being the case adding some extra resistance inline with the sensor would make the controller think the temp is cooler and hence switch the fan on at higher actual temps.

[Delk]

When I was young I had a fan switch because I couldn't afford to replace the sensor on my car. I wouldn't mind turning it off for water crossings but the fan normally stays on all the time when the engine is at full temp. Nothing drastic but I would like it to come on and off.

The upper hose is always hot so once the fan comes on it doesn't like to go off. If it was controlled at the rad outlet side it would only come on when the rad was not cooling enough. At least that's my thought. But most of the sensors are set higher then you would want on the cool side.

[eastryjeep]

Does your cylinder head have a port on the rear on the manifold side like the old 4.2 head?
If so you could install a sensor there for the fan switch and use the coolant temp as a sanity check wired to the dash.
Like that you could go wading with a switched fan and have readings for cylinder head and coolant temps.

[Dave69]

With big engines you control both the outlet temperature and the inlet since you don't want to overcool the inlet.

The thermostat should always maintain and engine outlet of around 90 degrees. But depending on air flow the radiator will have a different cooling effect so the inlet temperature will be up and down. My thought was if the sensor was on the rad outlet it would turn the fan on when the engine inlet temperature started to rise above a set level. Say 90 degree out and roughly 60 degrees in.

you are correct in what you are saying, but most of these installations and O.E equipment the cooling effect of the radiator is known, thus the temperature where the sensor is placed can be set to meet the required operating temperature.

replacement radiators dont come with a cooling efficiency information list of what temperature drop is to be expected when run operating. If fitting after market monitoring then top top hose makes sense, with a fan cut on temperature of 95 to 100 deg C, and by that the outlet temp should be a 10 degree drop on average.

brazed tube and fin radiators give the best thermal efficiency in regards to cooling but are prone to fin damage. Alloy radiators will take allot more punishment but their efficiency is less hence the pack size is increased.

Stainless steel is even better and its physically stronger in so many ways allowing for thinner wall sections but it's cost prohibitive to make