News from Austria: C02-Visco

After improving the Viscous-Coupling of the T3-Synro with a special valve and solving the oil-sucking-problem I was thinking about how to make our VC even better.

I reflected on how to increase the life span of the VC, because the silicon-oil is aging at high temperatures. By using a decoupler this aging can be minimized, but not everyone is willing to refit one.

I was able to document the process of aging by an on- and off-road test over 10.000 km with the following setup

  • 2mm unequal worn tirnes
  • maximum speed (110km/h)
  • off-road in sand

After six month of testing I measured the VC once again on the test rig and got the following result.

Aging VC after 10tkm
Aging VC after 10tkm

You can clearly see the increase in viscosity and hump-temperature. Therefore I recommend a lower hump-temperature – because it’s steadly increasing. The process decelerates over time, but after 200 to 300.000km the VC will look like that:

VC 300tkm

The viscosity of that aged silicon oil in the VC would be like 60.000AK. Such a VC wouldn’t damage the transmission, but parking without power-steering can be quite hard.


The process of oxidation can be avoided by replacing the oxgen from the air with CO2. W.Peschke researched this phenomena in his dissertation and provides some evidence about that:


And also the german silicon-oil manufacturer “Wacker” writes about a higher temperature-resistance of the silicone-oil in a CO2-atmosphere.


With the help of a vaccum pump I was able to degas the silicon oil and replace the oxgen with CO2. Also interesting is the amout of dissolved air in the silicon-oil. Here you can see a short clip of degassing silicon oil.


The degassing takes quite a long time (48h) – unfortunately otherwise gas-bubbles will make problems with the filling.

Continous test runs have already shown the non-existing aging of the C02 Viscous-couplings. But in addition I also made an on- and off-road test over 10.000km.


And here you can see the before and after diagram:


As you can see, there’s practically no aging of the silicon oil. Although unequal worn tires were used for the test-setup. In the future I will  sell the improved CO2- Viscous Couplings only.