Checking viscous fan

[jay see]

I found this link http://silvertonrads.co.za/technical/viscous-fan-clutches-–-how-do-they-work-and-what-is-the-correct-way-to-diagnose-them/
It explains how a viscous clutch fan works and how to correctly test them.
Now I know how they work, but not how to correctly test them.
Interesting it states 5% slippage and that the fan is engaged even at start up (cold temp). Makes sense that's why there's a big roar.
I'm looking at this because I'm still not completely happy with my system. On Friday I got off the freeway and sat at the lights for a bit and the temp raised enough to cut out the a/c. This tells me that the fan is not working correctly, does not happen when outside temp isn't that high.
I think I would be able to test with a timing gun and a infrared temp gun.
I've always thought at 1/4 turn by spinning by hand was a good working fan 1/4 turn is 25% slippage.

[mudnut]

They are talking 5% at engine speed, not 5% at standstill. It is normal for a fan to rotate 1/4 turn when pushed by your hand. That shows that there is a reasonable amount of silicon oil in the clutch. Also check there is no excessive slop in the bearing. The test that they recommend shows that the fans thermal control is working as well.

[threedogs]

I have a thermal gun here if you need to test your temps
You can buy coupling fan fluid from Toyota very cheap.
When you cleaned the radiator did you get it rodded, as
it may be partially blocked on the inside

[jay see]

Thanks for the offer TD, but I should be able to get my hands on one.
No didn't get it rodded.

[threedogs]

Whats the plan re-co the fan to eliminate it from the problem?

[jay see]

Whats the plan re-co the fan to eliminate it from the problem?

Yeah, or get a new one, with a new thermostat. That way I can eliminate both.
Had overheating issues on my last 4x4, hope to sort this out quickly and cheaply.