hot running 94 e 320 cabrio

I have had a 94 e 320 coupe for nearly 20 years now and at present am up to 215,000 miles, the engine has always run at fraction below 80 on the temp gauge in all conditions, I also have a 94 e 320 cabrio, which runs just over the 80 and when in slow traffic rises quite alarmingly, I have never allowed it to get dangerously high but in the event of being stuck in a really bad jam I am nervous to take it out, my local garage has changed the viscous coupling fan but with no result of cooler running,
can anybody give me some ideas where to start to look for the problem
Thanks
Torsp;