Topping up a viscous fan - what effect?

Hi all,

Having problems when towing the camper with the Courier uphill on hot days.

I think I've narrowed it down to two potential sources. I've got two possible problems.

First I'll look at is cleaning all the bugs and crap out of the air con condenser. It needs to be done anyway, and I hadn't realised how bad it was.

The second is the viscous coupling which appears at the moment to be working in some manner approximating normal.

But if I wanted the fan to work harder - pull more air - and not slip when it's at the lower end of it's lockup threshold, would adding more fluid make it do that?

The symptoms I'm getting when towing the camper (1.4 tonne) on a really hot day are that when I hit a hill - say the climb into Omeo - I can hold speed (eg. 60kmh in 3rd) and even accelerate so I'm not at the limit of the gear, but after half of the climb the temp guage climbs toward hot rapidly.

Dropping back to say 40kmh and 2nd gear the temp guage drops rapidly. (Dropping speed staying in 3rd just ends up dropping out the bottom end of the rev range and it labours.)

In anything less then about 32°C its not a problem at all.

I've noticed it once before a few years ago not towing when I was heading to Ceduna. Trying to hold 115-120kmh into a hot headwind did it, which I put down to effectively trying to drive it at 140kmh (counting the headwind) in hot weather. Dropping speed back to 100-105kmh fixed it then too.

I've got some of the Toyota viscous fan coupling fluid. I'm wondering if it's worth performing surgery on the fan.

Dave