Lazy thermostat?

[kilo]

I own since 10 years a Spider. It was imported from the USA to the Netherlands. A while ago, I replaced the waterpump in my Spider. It has a 1592 CC engine, T-stat on top of block.
Since then the temp gauge behaves different. When warming up, the needle overhoots 190. About halfway to the red zone, then returns to 190, then an other overshoot and finally stays at 190 and works fine. Before the waterpump exchange there was no overshoot to speak of.
Radiator fan works as it should. I changed the t-stat, thinking that might be the culprit, but no change.
Carefully 'burped' and sucked the air out with a vacuum pump. ( Flushing tee's do not exist here in the Netherlands)
When I warm up with the heater on, there is no overshooting needle.
Could it be caused by uneven heating in the block, ( T sender gets warmer than T stat) due to airpockets, or due to marginal flow in the block when T stat is closed?
And, is this this a problem that should be fixed? Could this uneven heating distort the block seals? Or is such an overshoot a marginal thing?
I'd love to read your expert opinons on this.

[131]

I used to work in a Fiat/Lancia workshop, on some cars we'd drill a 3mm hole in the thermostat to allow more bypass. It took slightly longer to get up to temperature, but it allowed enough flow through the head to stop the high temp spikes.

[kilo]

Thank you for this advice. There is already a small hole in the T stat. With a little cupper piece in it. Will drill another hole in the t stat and see what happens.

Did so today. Unfortunately, it did not change the spiking. Does slightly lower the warm up time..