Problem Cooling System – Help…

Hello dear Schraubergemeinde. I changed the cooling water last time on my B3 Coupe with the 3A 113 HP engine. Now I have occasionally the problem that with sharper curves the coolant warning light flashes briefly. But in the balance tank is actually enough liquid in it. From what comes that then??? Besides, is the normal that the dare needs almost 15 km until it is really warm? Can naturlcih also come from the cold temperatures at the moment, but how is that with you??? Did I v ielleicht not properly exposed?? Have already used the search but there was a nothing really helpful…. Greeting flo