As I have posted in the past, I'm still chasing high coolant temps after that head gasket repair. But as part of my on-going diagnosis, I have felt my radiator temp across it's surface by hand, and in-fact did so just the other day when the outside temp was about 20F, just after I pulled into the garage after a 35 mi run at 50mph average.
I noticed that the radiator is very cool in all spots other than the upper RH end. I believe that as the ambient temp goes down, there is not enough flow through the T-stat to heat the radiator uniformly. I did pull the radiator and filled it with hot H2O on the bench with the rad in the horizontal position. and that test yielded uniform temps across the entire rad. Based on that test, I suspect that the rad temps would not be uniform during cool weather.
I am just passing along my experience, but I am coming to the conclusion that my problem is either low-flow from the water pump (I don't know how the pump is constructed and if it can possibly fail in that manner) or that I have a debris blockage in the block or head. I also have low flow through the washer fluid tank coil as it just doesn't heat up the washeer fluid like it did before the head gasket repair.
Good luck, and thanks for your past posts on my cooling adventure.
1995 E320 Sold at 288kmiles