Have fitted dual AU fans in my XW (with plenty of modding!) and am planning to use two separate sensors to activate them. I am considering surface mounting the sensors on the outlet radiator tank (XD 3-core crossflow type) to measure the temp of the coolant entering the engine.
As the standard temp gauge in the car is probably pretty average to say the least, I was looking at lowering a temp probe into the tank to measure the actual coolant temperature. The switch/senders I am looking at come in 5 degree increments (eg 85, 90, 95, 100 degrees etc).
So, the question I have is what value temperature switch should I select to have the first fan come on, and what value temp switch would be the best to have the second come on? btw - have no idea what thermostat is fitted!
Well water boils at 130 degrees under pressure, and as high as 180 with antiboil/antifreeze added.
I would probably set the first one at 90 and the second at 100 to start with then adjust from there, if you think the engine is getting too hot before they kick in then just adjust them, or too cold before they start for that matter.
I did put something here, but it vanshied, I think
Thanks for the replies! The switches I am using are non-adjustable, you can get them from most electronics suppliers. Hence the reason I was asking about suitable switching temps - I guess the other way is to buy a heap of different temp switching values and go for the trial and error method!
I figured by surface-mounting them on the outsider of the outlet tank, you get around the problems of having a capillary tube going through the hose and all the associated potential leakage problems.
As these devices are fully sealed, they should be quite robust - just hook 12V to one side, and when a certain temp is reached, they close the circuit inside to apply power to the relays.
If you wanna be really sneaky, use the fans as they are designed to operate on the AU, with high and low speeds for both. The factory setup has 3 relays to acheive this, 2 normally open relays and a change over one.
With my NB Fairlane I used surface mounted thermo switches from RS Components/Altronics/Jayacar etc mounted in an L shaped aluminium channel that I sat in the channel on top of the radiator and rivetted to the side. I experimented with a range of thermo switches (and their placement) and found you needed opening temperature values about half that of the coolant temperature you wanted them to open at. The distance from the water channel in the radiator means that the coolant is a lot hotter than the surface temp of where the switches are mounted.
If you wish I can dig out the actual temps I used (something like 35 degrees C and 50 degrees C as far as I recall) and some pics I took of the set up. I would counsel against screwing straight into the top of the radiator; as I found it is just far too easy to hole the radiator core. I also suggest that as I did, and to improve the conduction of heat to the base of the switch, you put some Unick Thermal heatsink paste between the botton of the thermo switches and the surface they are mounted on.
Thanks for your replies. I will probably be just running each fan as a single speed (although the variable speed idea is attractive, I am currently set up for the single speed). However, I like the idea of mounting the switches in the channel, but will probably have to experiment as there is no cooling tube directly contacting it. Hence, will have to investigate how closely the temperature in this area follows the actual coolant temp. Looks like a bit of fiddling about with a temp probe!
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