electric fan thermostat switch

[beasterly]

Trying to figure out where it should go I have read on multiple forums the back of the head but I would think the thermostat housing . motor is a 250 inline any advice would be greatly appreciated .

 

[707Bronk]

I spliced my 2spd fan switch into the upper radiator hose.

 

[beasterly]

I have a single fan for now

 

[Viperwolf1]

Back of the head is too cool. Coolant picks up most heat as it goes forward through the heads. Take the temp at the front of the manifold or even thermostat housing.

 

[AxlesUp]

mine is in the thermostat housing.

 

[beasterly]

I have a inline 6 no intake I have a port on one side in the back other side in front next to exhuast manifold one on the thermostat housing . thinking thermostat for the the fan switch and front of head for temp sensor . anyone disagree ?

 

[beasterly]

I did a motor tranny swap full body resto and moved so 2 years later I'm trying to hook everything back up and clean up the wiring so want to get it right the first time .

 

[Viperwolf1]

I have a inline 6 no intake I have a port on one side in the back other side in front next to exhuast manifold one on the thermostat housing . thinking thermostat for the the fan switch and front of head for temp sensor . anyone disagree ?

Coolant flow is the same on the six, from back of head to front. Front of head temp is going to be much greater than rear.

 

[beasterly]

When I bought it 6 years ago the temp sensor was in back of the head thinking it should be where it's the hottest in the front . Thermostat switch I'm guessing should be in the housing because I want the fan to turn on when hot water is pushed into the radiator to cool it off correct ???

 

[suckerpunched]

Thermostat switch I'm guessing should be in the housing because I want the fan to turn on when hot water is pushed into the radiator to cool it off correct ???

Well there are two ways to look at that, I wanted to put mine in the thermostat housing but ran out of room there. I needed a splice in my lower hose, so I put it there. My controller is adjustable to kick fan on in low down to 160 degrees. So hopefully I can dial it in. It really does not matter how hot the water is going into the radiator as long as it cools down before it leaves the radiator. Air flow at highway speeds or what ever may do it with out the fan. At least thats how I justified it but mine is untested. I know other people here have made it work like that.

 

[Viperwolf1]

Well there are two ways to look at that, I wanted to put mine in the thermostat housing but ran out of room there. I needed a splice in my lower hose, so I put it there. My controller is adjustable to kick fan on in low down to 160 degrees. So hopefully I can dial it in. It really does not matter how hot the water is going into the radiator as long as it cools down before it leaves the radiator. Air flow at highway speeds or what ever may do it with out the fan. At least thats how I justified it but mine is untested. I know other people here have made it work like that.

The coolant return should be much cooler than 160.

 

[ntsqd]

At one time I had a temp gauge at the cross-over port in the intake of a 302 and another at the rear of the RS cyl head. The rear head gauge always was colder than the front on a cold start, but once warm they agreed within the accuracy of the gauges. When working the engine hard the rear of the head consistently ran warmer than the front by 20°-30° My theory for explaining this is a combination of coolant flow at the front vs. the rear and hot vs. "cold" dilution. Note that this was after adding rear to front coolant plumbing in the intake manifold to try to increase coolant flow at the rear. I've no before data because the ports didn't exist until that experiment.

All of that said, that car ran one electric fan and it's old school t-stat bulb was in the upper radiator hose at the radiator.

 

[CraigS]

Well there are two ways to look at that, I wanted to put mine in the thermostat housing but ran out of room there. I needed a splice in my lower hose, so I put it there. My controller is adjustable to kick fan on in low down to 160 degrees. So hopefully I can dial it in. It really does not matter how hot the water is going into the radiator as long as it cools down before it leaves the radiator. Air flow at highway speeds or what ever may do it with out the fan. At least thats how I justified it but mine is untested. I know other people here have made it work like that.

This ^....

You're turning on the fan to cool the radiator water when the radiator gets warm. If the bottom hose (return to motor) never gets warm, you'll never need the fan on.

 

[707Bronk]

If you have an adjustable thermoswitch then it doesn't really matter where you put it so long as you have enough adjustability.

With a fixed thermoswitch the lower radiator hose will cause the fan to come on later. But the only time it would cause a problem is if the fan doesn't have the CFM to catch up since it would turn on after the radiator has maximized its cooling capacity.

I'm not sure what the cooling capacity of radiators are (now I want to put an IR gun on my inlet and outlet), but if it was able to cool it 40° and you wanted your fan to kick on when the coolant temp is 205° and if you were spliced into the lower radiator hose then the fan wouldn't kick in until your coolant temp was at 245° with a fixed thermoswitch. That "might" be pushing it a little, especially if you had a weak fan. Now with an adjustable thermoswitch in the lower radiator hose you could set it to 165° and still maintain the 205° setpoint.

 

[ntsqd]

A 40° delta might be optimistic, I've heard as low as 20°

 

[707Bronk]

A 40° delta might be optimistic, I've heard as low as 20°

Yeah, I just guessed. Even at 20°, if you had a 205° setpoint it would still kick on at 225° with it located in the lower hose which isn't too bad, but still 20° higher than it could be.

I guess the question is what is the proper temp your fan should kick on? And then select your thermoswitch setpoint depending on where you want to install it.

 

[suckerpunched]

I just revisited the specs on my fan controller. low speed can be adjusted to come on as low as 150 degrees. second speed kicks in at 10 degrees hotter. so even at a 40 delta, it should work. thermostat is 195 I feel like the fan should kick on in low at some point a little hotter than than that maybe 205/210 ish.

I have to admit though, I wasn't worried about it not working. But when viperwolf says it won't work, I gotta take that fairly seriously.

 

[pbwcr]

Some technically correct posts are above. Let me summarize the correct.
The rad fan is to control the rad temp. The thermostat is to control the motor temp.
(Do not mix up these two things. The gauge on your dash measures motor temp and is located by the motor designer. Not something one should mess with).
If the rad gets to hot then the motor will be to hot due to lack of cool fluid.
So the rad fan has to have its own sensor at the outlet of the rad (cool side), and not anyplace related to the motor temp. Best place is in the lower rad hose or a bung in the bottom of the rad.
About thermo switch and most controllers. They suffer with huge variable dead band which means unpredictable on or off set points. This is because what is used is a bi-metallic leaf the makes and breaks the contacts. Contacts get old and big variation occurs. They are susceptible to vibration which further degrades performance and shortens life. And except for pricey industrial units they are cheaply made for the consumer market.
I have slowly migrated to more modern control. I am using a modern gauge with internal chip that will operate a fan via relay. Most high end T gauges have two set points which are set by reading the gauge. My experience is they are very accurate and are easy to reprogram. Dead band is very small meaning the on and off are close to each other. If one wants to have a two stage fan then just set the thing to operate at two different set points.
I am now using two brands - Autometer Sport Comp II, and Speedhut. I like the Speedhut best for ease of installation and custom gauge face options. Neither are cheap and both perform in an excellent manner.
So that is my input for you all to consider.
Regards, PaulW

 

[brianstrange]

Does anyone have a list of auto manufacturers that place the radiator temp sensor on the lower side of the radiator, and know what they use for a temp setting? I've never heard of this practice, and would like to learn more. If the sensor is being placed after the coolant flows thru the radiator, the fan turn on setting would need to be much lower than if at the top. I would have thought metering the temp as it exits the engine, would be a more reliable source, and give a direct command that the radiator will need the aid of the fan BEFORE it passes thru the radiator. The only benefit to lower position that I could guess is in the event it runs low on coolant.

 

[ntsqd]

In the lower hose or cooler side of the radiator does seem to me like it would delay the fan response to a change in condition. Maybe that's on purpose?