308 QV getting too hot

must be a common subject during the summer months. Seen several threads "like" this one but not exactly so had to start my own (yes, yes.. I did a search).

84 308QV. radiator cooling fans will not turn on while engine is running. water temp goes above 195, while the car is moving it's not a big problem but when stuck in traffic temps approach 200+ and the fans don't kick on.

If I stop the car, turn off the engine and put key on aux power, fans come on and stay on until temp drops below 195 (like they should).

so my Q is, what would cause the fans to work when the engine is OFF, but not while it's ON. seems to me all sensors are working if they work at all.

Could it be that I just need to bleed the system? thoughts?

thanks.