viscouse coupling sensor

after my previous posting it would appear that i was indeed being paranoid. i have had my vc checked out, have run it up the motorway and hills, and it appears to be working fine (touch wood).

as this was of concern to me, and by the sounds of it to a lot of you as well, i have continued to devise a sensing device so that we can all get tangible evidence that the coupling is working.

i started to build an anemometer to sense the flow of air produced by the fan.
i have done this by using a small dc motor from an old cd drive that opens and closes the draw. then i attached a propeller from an old toy. this combination works fine as the motor is efficient enough to produce a small charge, whilst the propeller is inefficient enough to not stall the air flow and cause hot spots on the radiator. i have mounted this inside the cowling of the radiator and hooked it up to a digital volt meter inside the bus to see how much voltage is produced.
the results are a bit up and down as the anemometer is sensing air flow, and there is a degree of lag caused during speeding up and slowing down of the propeller, so the voltage is not in time with the engine.

then, through a business contact , i met a chap who got really excited by this project. he has recommended an electronic sensor to measure the speed of the fan, with a series of led’s mounted on the dash. this way the faster the fan is driven, the more led’s light up. this then becomes a very accurate sensing device that gives a true indication of the fans speed. this idea is still in the planning stage and will be a while before its tested.

turns out that this chap used to design cooling mod’s and sensing circuits for nuclear power stations. hopefully then the townie wont present any special problems for him.

i will let you know how we get on with this one

dave bright





- (#5968) dave Bright, 30 Oct 02

sounds very interesting and very useful to us townie owners who havent fitted electric fans,
keep us informed Dave.

- (#5969) ron coe, 30 Oct 02

Yes, I'm sticking with the viscous coupling and have been thinking about some form of test too, though I favour sensing the fan rotating rather than the airflow.
The airflow through the cowling is not just due to the fan, some is scooped in by the car's movement. On the other hand the fan's rotation is not only due to the viscous coupling either, to some extent it will be blown round by the ram airflow - unless restrained e.g. in the "thread test" described elsewhere.
I dream of a something low-tec, like a wooden lollipop stick just touching the fan blades, possibly enough to stop them rotating some of the time. This would just be a temporary thing, trying to verify the coupling is not u/s and does work some of the time - when I'd hope to hear a buzzing sound. In know about the reported "V8 roar" but frankly I've never heard it, nor do I get any signs of overheating.
Can anyone whose coupling definitely works, confirm if you pour boiling water from a kettle over the viscous coupling (engine stopped) - then you can feel the coupling lock? I haven't tried it. I can't find a reference to the temperature at which it should lock.
Ultimately that coupling is only one of the cooling faults that can surpise you and you need to know about. E.g. there's a burst hose, thermostat stuck shut, even head gasket dying on its own and expelling the coolant. So surely modifying or replacing the head temp gauge/alarm is the catch-all solution.

- (#5970) Dave Mason, 1 Nov 02

Dave,
"Can anyone whose coupling definitely works, confirm if you pour boiling water from a kettle over the viscous coupling (engine stopped) - then you can feel the coupling lock? "

The rise in temperature, of the viscous coupling body,from boiling water or ambient air temperature, will open the thermostatic valve which controls the flow of the viscous fluid from the "slipping" chamber to the " driving" chamber. However, I think I am right in saying that the fan needs to be rotating for this fluid to pass to the "drive" chamber, via, what is known as a "scoop valve". I don't think that you will ever feel the coupling "locked", even if the radiator temperature (and the air passing over it)is at a maximum. The difference in "drag", of the coupling, can certainly be felt if a quick manual test is made after a long run, ie, when the rad/engine/coupling etc are all hot. There are, I am sure, viscous couplings which have various refinements but, I think that the Toyota one operates on the two chamber priciple.
Dave's note above, ie, an electronic sensor, sounds ideal and I look forward to learning more. Before I replaced the v/coupling on my fan, I experimented with a small magnet, bonded onto the coupling body, with a non magnetic block diametrically opposite for balance, passing in close proximity to a magnetic switch, linked to an LED. It was a bit "Heath Robinson" and was not an ideal solution.
I like the viscous fan setup and I think that it suits the vehicle. Now that I have an accurate temperature gauge (Durite) a new coupling, and a 30mm opening thermostat with "by-pass" holes, I feel that I have gone a long way to ensuring maximum cooling efficiency/coupled to the best early warning system. So far, it seems to work quite well but Dave's electronic fan speed sensor might be the icing on the cake.

- (#6010) John Davis, 1 Nov 02