912is High Coolant Temp - Fan?

I'm a new plane owner (912is) with a new plane (70hrs).  So far it has been performing exceptionally well.  My home airport has a rather long taxi to the runup area and I noticed yesterday that the coolant temps were running into the red after run-up and waiting to take off.  After taking off, the coolant came back to normal and everything was fine.  Ambient temps are around 65F.

Flew to an airport an hour away overnight and has a very short taxi area and I was overheating very quickly, in fact Lane A was flashing; maybe 68F ambient.   Saw the coolant issue, reduced throttle.  Lane A reset did nothing and eventually went solid red.   Taxi'd back to parking to let it cool for about 20 mins.  Startup was fine, temps were climbing again, but got an immediate release and took-off.   Temps were fine the whole way home.  There was a stiff 15kt crosswind in the run-up area that may have disrupted airflow across the radiator.

As we start getting into the summer, temps will get over 90F regularly and if I'm having issues now...I can't see summer flying even being an option.

Details / questions:

1. I was using 91Mogas exclusively until I went to the new airport.   They topped off with 100LL the night before (at startup 1/2 was 91 and 1/2 was 100LL)

2. It's using Dexcool Longlife GM 93170402.  Overflow tank is about 1" above the min line and hasn't moved as far as I can tell.  Should I top it off?  Should I use something else?  I don't think it's 50/50...but I don't really know to be honest.

3. I recently upgraded the prop from a basic manufacturer provided prop to a better aftermarket carbon fiber prop.  The old prop was wider (very scientific), so wondering if that was giving better airflow over the radiator. Ground taxi at the same RPM (1700) feels higher with the new prop.

4. When I got home and let the engine cool, I opened the coolant cap and it was full to the top.

5. In flight temps are perfectly fine; about 100-110F over ambient at high cruise.   50F air temp, 160F coolant temp.

6. Instead of the run-up area full stop, 4,000RPM lane check procedure...can I instead do it during taxi at lower RPM (since we are just checking the lights are working)?   As far as full-power, I'm checking that at the end of the runway anyways before I release the brake.

7. Could I install a 12v fan on the backside of the radiator; perhaps with a cockpit switch to make it simple?  If so...where could I find one?

Thanks for the ideas....