High oil pressure on startup

Until the oil is warmed up to 50C (122F) you should not rev the engine past about 2500.  Until then it will be too viscous for higher revs. If you do rev higher, your oil pressure is of course going to go up, probably higher than you want it; it will start to bypass the filter, etc.  If you went up over 100psi for very long, I would start to worry, as 100 (102 max, per the manual) is the absolute top end of the pressure range.  I wonder if, when you went over 100, the oil started to bypass the filter, bringing the pressure back down quickly after those 1-2 seconds.  Having pressure that then decreases with higher revs is definitely not a good thing, I would say.

What oil are you using, by the way?

Well, what I mean to write is that reving the engine meant going between 2000-2300 during warmup, just as I have done every time I start the engine in the last 500 hours or so.

In other words, I have been doing the same thing as always but this time PSI went up to 100 for a 10 or so seconds and then within span of 1-2 seconds went down to my usual range.

I have been using the same Aeroshell Sport Plus 4 oil for all of my 500 hours with this plane.

I am gonna try to plug a mechanical gauge and see if I can replicate the same spike at the start...

Be sure you match the threads on Mech Gauge with the Sender.
Some Oil Pumps are 1/8 MPT (~3/8x27 Tapered Threads ) and some are M10x1 (Straight Threads)
They are so similar that they will start to thread a few turns on each other before cross-threading!   (Roughly  0.405 x 27 vs. 0.394 x 25).
Don't be THAT Guy!

1/8 Pipe to M10 Adapters are available at any decent Auto Parts store, Amazon, eBay, etc.

I am pretty sure my engine uses M10 given that is from 2012 but I will double check.

Thanks for the reminder.

One more question …assuming this is metric, would this sender be appropriate replacement ?

https://www.summitracing.com/parts/vdo-360023