The old school method for dealing with coagulated oil in the cooler and the resultant oil pressure rise was a spring loaded piston in the accessory case. In normal ops, the oil flow goes 100% to the cooler, but in the case of a restriction, the piston will lift and bypass the cooler. The current vernatherm has this feature as well, but experience indicates the sealing capability of the cone seat is wildly variable and as a result, some engines do not see the cooling oil flow they need. The viscosity valve is VERY effective and can completely transform the oil cooling capability of a given engine. This valve is discussed at length in the threads dealing with a "ball valve" for controling oil flow in winter ops. A search should bring up many examples.
WARNING! Incorrect design and/or fabrication of aircraft and/or components may result in injury or death. Information presented in this post is based on my own experience - Reader has sole responsibility for determining accuracy or suitability for use.
Harmon Rocket II -SDS EFI
1940 Taylorcraft BL-65
1984 L39C - SOLD
RV-8 - SDS CPI - SOLD