1985 300D slow to warm up

[louis4052]

As the weather has gotten colder in the northeast my 300d has been taking forever to warm up and almost never hits the 80 degree mark on the temp gauge. I have a greasecar kit in it and the coolant temp gauge on the co-pilot confirms coolant temps around 160 after 20-25 minutes of driving.
I have replaced the thermostat with a genuine MB and swapped the expansion tank cap with my 1985 300TD. Is there anything else to check out or is it time to put a winter front on this one? My wagon has always run hotter and never had trouble warming up in the winter.

Thanks!