Very strange temperature problem!

[Vaden85SEL]

Hi everyone,
I have searched all over this forum looking for an answer before I started this new thread, but I haven't come by anything that is similar to my symptoms. Hopefully someone out there can help

Anyway, I have a 1985 500 SEL and it runs fantastically. Lately however, when I start the car in the morning, the temperature guage rises steadily as usual, but it does not stop around 82-85 degrees like normal. The temperature continues to climb until it is almost into the red and then immediately, as if the thermostat were just opened, it drops down to normal operating temperature in a very fast drop (from almost 120 degrees to 82 degrees in about 8 seconds). After this behavior, the temperature is fine all day... or until I leave it for a few hours to cool off completely.

Initially, I thought that my thermostat was being a bit lazy and not opening when it should... I thought perhaps the springs had gotten a bit sticky or perhaps it needed a bit higher temperature to "kick-start" the thermostat into opening. So I replaced the thermostat all together, but the problem still persists. It really isnt an emergency because the temperature always comes back down after only briefly being too hot, but I fear that the problem might get worse with time and I would like to nip it in the bud now before something horrible happens. Perhaps there is something electrical going on? Or perhaps there is a second thermostat that I am unaware of? Perhaps a faulty temperature relay?

Any suggestions would be greatly appreciated! Thanks!

-Vaden