I have been having an underheating issue with the B20 in my 122. My engine has a fuel injection head with dual SU's attached via a combined intake/exaughstlmanifold, and a mechanical advance distribitor off of my B18 set to 30 degrees BTDC.

When driving around town the car performs great, when the weather is hot the idle is a bit high though. When I go for a run on the highway at high rpms (don't have an OD) the engine cools down to a point that it won't idle when I get off on an exit. This is worse when the weather turns cold. I know that my thermostat is good, and I have tried another of the same rating with no difference. My next thought was to try a hotter thermostat, or even trying to find a used viscous coupling fan. I have no experience with these fans, but I have read that they are supposed to slip at higher rpms, maybe enought to reduce the cooling effect on the highway.

So what should I try next? A hotter thermostat (do they make them hotter) or a viscous coupling fan? Any ideas and suggestions are greatly appreciated.