Good answer from JonSnell Electronic...
The reason it is a good answer:
Your
TEMP GAUGE is only reporting the news
(not making it).
Any leak or defect (cold pressure tester)
will inhibit
OPTIMAL PERFORMANCE
(which is exactly what is needed in a traffic jam)
Your car (and most cars) have a system built in to
allow for when the
FORWARD MOTION of the vehicle
is
NOT ADEQUATE air flow to cool the radiator..
The subsequent rise in temperature should trigger a
thermal
switch (see below) and electric FAN (below)
should come on to augment the AIR FLOW...
Check both electrically. Free Technical Service Bulletins and wiring diagrams are available from
BBB Industries (registration is required s these are real documents
You need to be looking here
BBB Industries Premium Alternators Starters Power Steering Products
Hope this helps!!