Question on BMW 3-Series E36 Coolant Flush

My 97 318ti M44 recently had a the water pump replaced. driving around on a hot day and the temp gauge slammed into the red. I pulled over, popped the hood and noticed coolant everywhere. Pretty inexpensive fix. drove almost 20,000km this summer across the country including a lot of high mountain climbs in hot weather with no issues. However, if I ever got stuck in stop and go traffic, after 10 min or so my temp gauge would start to climb again. it would never get into the red. just a little over the 3/4 mark. once I was out of traffic and got up to speed the temp would drop back down to normal. any idea why this is? and should I be concerned? now I have traffic anxiety haha.

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[Nick at Pelican Parts]

Your cooling fan may not be operating properly. Check operation of the mechanical and electrical cooling fans.

- Nick