thermo fan switch, install in inlet or outlet of radiator?

[matty12]

to keep things simple i would put the switch nearest to the thermostat, whether it be in the top or bottom hose.Have the temp of the switch turn the fans off at say 5c above the opening point of the thermostat.My reason being it may be hard to calculate how much heat the coolant will pick up travelling through the engine if the switch was on the outlet of the engine and the thermostat on the inlet, and in turn you may be closing the thermostat down or running too hot.Since the themostat control temps for the engine as to what temp is suitable i would work on that.

But on my 1uz the sender for the ecu which controls the fans is in the top, i selected 95 on 90 off and left it.Havent thought about it much since.

I can see merits in both ways, do what would suit you the most.

Ive seen many factory system that have the temp senders in different locations,some with the sender in the bottom tank of the radiator with the thermostat in the top hose and vice versa, or senders in the top of the engine with the thermostat.

[hemi twofifteen turbo]

The themofan most directly effects the temperature of the water exiting the radiator. It makes sense then to regulate the fan with a sensor looking directly at that output -- the outlet of the radiator.

The engine thermostat most directly effects the temperature of the engine. It looks at the temperate of the water leaving the block, that would be equal to the average block (or more realistically) cylinder head temp, and adjusts water flow instantly to maintain a temperature.

To run through a list of possible cooling system scenarios I see the bottom hose switch winning every time.

Hot stationary idling ---> Cruise transition
Although hot water is exiting the top hose, at say 85 deg, (which would make a temp sensor in a top hose think the fan should be on) The lower hose is showing maximum coolant temp drop, say 85 down to 45 deg, purely from the airflow generated from cruise air. In this transient situation the lower hose sensor adjusts the fastest to turn off the fan as it is now seeing 45 deg temps, even while the top hose is throwing out the last of it's 85 deg water.

Cruise--> Stationary transition
Coming to a stop after a cruise, the water exiting the thermostat is right on 78, the water exiting the radiator which now has no air flow changes from 40 to 70 degrees due to the lack of air flow. The switch in the lower radiator hose would sense this and activate the thermo fan. A switch in the top radiator hose would still be waiting for the temp to rise above 78.


Cruising -- Airflow causes cool water to flow from radiator -- no thermo fan



Driving hard -- Hot water >90 exits fully open thermostat but is cooled sufficiently by radiator -- no thermo fan required doing 150km/h -- thermo switch in top radiator hose could be activated in this case, when not required, consuming 200watts which would be enough to slow you down by 1/10000 of a second down the 1/4.

overheat situation -- air flow/radiator efficiency is no upto engines heat loading, this 'problem' would be noticed first in the lower radiator hose, even before a switch in the upper has a problem.. For example.. 80 degree thermostat, water exiting lower radiator hose at 78 degrees would well and truely have the thermo fans activated, but in a top hose situation would not. -- but either way not a good situation!



Honestly though I don't think it makes too much difference, although I did once have a hunting situation by placing thermo switch in top hose.


Anyway that's how I see it, such a simple thing so much discussion love it!

[Toy77]

Interesting guys....
I have just done this to my patrol.

The controller i have is digital. It gives me 2 temp inputs and voltage (designed for water and oil temp) and controls an output on one temp - which is my thermofan.

i have fitted the sensor to the top radiator hose where the thermostat and the factory temp switch are, and the system is running well.
I had planned on fitting the 2nd sensor into the bottom hose so i could see what the radiator was doing.
unfortunately i refilled yesterday with new coolant (9l of the stuff) and didnt fit 2nd sensor... so would have to drain again to do that - but would be interesting to see the comparrison.

I will consider it some more....

cheers'
Stew

[river]

Hi,

I had planned on fitting the 2nd sensor into the bottom hose so i could see what the radiator was doing.

When you do get the 2nd sensor pls let us know what temp it gives. It would be interesting to see the difference (between it and the top sensor), particularly through various driving conditions and ambient temperatures.

Are you going to do anything with the 2nd sensor, such as have some control process or other logic to control the fans etc, or just use it as a temp gauge?

seeyuzz
river

[Toy77]

No the 2nd sensor is simply a temp guage. But they are identical - so i can simply swap the plugs at the back of the unit to control the thermo off the other sensor if that makes sense.
I actually bought 2 of the aluminium mounting blocks to mount both of these - but unfortunately i looked in supercheap for the hose sizes to buy the mounting block to suit - and one was wrong - so i had the incorrect sized block for one hose.

Of course this was the first one i fitted the sensor too - so had loctite 515 over it, and couldn't be returned.
Hence why only one is fitted... but i may remedy this shortly, as it sounds like an interesting experiment if nothing else.

Cheers
Stew

[kewp]

My particular engine has the thermostat and gauge/ecu temp senders in the outlet side of the radiator (engine coolant inlet).
In this case, the outlet of the radiator will always be at the thermostat's control temperature (82 deg assuming enough airflow through the radiator). It doesn't matter what the temp of the water exiting the engine is, the thermostat will always aim for 82deg engine inlet water temp, it will vary the water flow rate as its control variable. Therefore the temp of the water in the bottom pipe should always be 82deg (or very close to it). This is only true when there is sufficient airflow to cool the water in the radiator to 82deg.
In the case when there is insufficient airflow, the thermostat will eventual reach its control limit and the radiator outlet temp will rise, this is when you want the fan to come on. Therefore I think the switch should be in the radiator outlet hose and set to a temp slightly higher than the thermostat temp.

The temp of the water exiting the engine will be highly dependand on how far open the thermostat is, and not necessarily how much heat the engine is generating. For example, cruising along at a steady 100kph, the thermostat will be almost completely closed because there is so much cooling air flow available, therefore amount of heat removed in the radiator will be very high. Thus the water flow rate through the engine will be low because the thermostat is almost closed to achieve aim water temp. So the water flow rate through the engine is very low, but the engine is still generating a moderate amount of heat, so the water temp exiting the engine will be very hot. The engineers who designed the cooling system will have done all the maths to ensure that the water exiting the engine won't be hot enough to boil under the worst conditions, based on a constant inlet temp of 82deg and variable flow rate.
This is why a lot of factory cars ecu's will turn the fan on automatically for a short time if you are cruising at high speed and suddenly come to a stop, even if the water temp is still ok. They do this because at cruise the water temp exiting the engine is very high, when you suddenly stop the radiator cooling ability is completely lost, but the water temp is still very high, so the engine temp can rise quickly unless you find a way to increase the airflow (switch the fan on) until the thermostat has time to react. This is different to a situation where you've been sitting in traffic for ages, and the thermostat is 100% open, therefore the water flow rate through the engine is very high and the temp rise accross the engine is low, thats when the fan will cylce on and off based on coolant temp.

[matty12]

The temp of the water exiting the engine will be highly dependand on how far open the thermostat is, and not necessarily how much heat the engine is generating. For example, cruising along at a steady 100kph, the thermostat will be almost completely closed because there is so much cooling air flow available, therefore amount of heat removed in the radiator will be very high. Thus the water flow rate through the engine will be low because the thermostat is almost closed to achieve aim water temp. So the water flow rate through the engine is very low, but the engine is still generating a moderate amount of heat, so the water temp exiting the engine will be very hot. The engineers who designed the cooling system will have done all the maths to ensure that the water exiting the engine won't be hot enough to boil under the worst conditions, based on a constant inlet temp of 82deg and variable flow rate.
This is why a lot of factory cars ecu's will turn the fan on automatically for a short time if you are cruising at high speed and suddenly come to a stop, even if the water temp is still ok. They do this because at cruise the water temp exiting the engine is very high, when you suddenly stop the radiator cooling ability is completely lost, but the water temp is still very high, so the engine temp can rise quickly unless you find a way to increase the airflow (switch the fan on) until the thermostat has time to react. This is different to a situation where you've been sitting in traffic for ages, and the thermostat is 100% open, therefore the water flow rate through the engine is very high and the temp rise accross the engine is low, thats when the fan will cylce on and off based on coolant temp.

I dont agree with that and will alter from vehicle to vehicle.At idle the engine will be producing the least amount of heat and require less cooling as it not working hard at all,at 100 or so the engine will be producing more heat, this why if you have a partially blocked rad it will be more likely to overheat at speed then just crusing at low speed around the burbs.

[OnAll-FOUR]

I agree with KEWP I think it can be viewed a bit more simply than some of you are suggesting?

I know that the factory thermo switch on the 3SGTE is on the water outlet from the radiator. I think the factory point of view is looking at it simply, If that water temp is too high, then the radiator needs help to shed the heat so the fans come on (regardless of the cause, too much heat from engine or not enough cooling). In factory config this appears to be as River said above the termostat of the engine.

The dash gauge and ECU temp measurements however is taken from the water outlet. This is so that it knows what the actual operating temp is of the engine at the hottest point and can warn the driver and recalibrate the ECU to take action as well.

I also agree with Rivers point of by this time it seems it is too late, hot water is already going into your engine and it will take some time for the thermo fans to bring that temp down. I have programmable ECU which has thermo fan control and was wondering if there is a way to improve this but this will be based on the water temp measurement point from water exiting the engine.

I have been thinking I could connect both controls to the temo fans (temp switch and ECU), that way the factory switch will work as factory. But when the car is working hard, I can also have a higher setting on the water outlet to start the thermo fans early and hopefully give the radiator a head start. My only concern is that with this high side switching is that maybe it could end up cooling the water too much and make the water coming out of the radiator too cool? I think with some smart arrangement of the relays i can get around this though

I tried to get some ideas for this in one of my old threads but nobody seemed to care about it
http://www.toymods.org.au/forums/showthread.php?t=52034

Also the infamous thermo fan wiring FAQ
http://www.toymods.org.au/forums/showthread.php?t=95

[kewp]

the best way to control a thermofan would be based on feedback from the thermostat itself, that way you could turn on the fan before the thermostat reaches 100% and maintain it within its control range. Of course this is impossible unless you have some variety of high tech thermostat that can feed its position back.

[allencr]

the best way to control a thermofan would be based on feedback from the thermostat itself, that way you could turn on the fan before the thermostat reaches 100% and maintain it within its control range.

Does this thermostat get controlled by flow from the bypass on then back of the head that might be a little cooler then the exit to the radiator in the front of the head?
This fan will run regardless of the ambient temp & the radiator's heat dumping performance, only on engine temp. and run almost continuously, won't it?