I have an old Yanmar 2QM15 - It has a temperature alarm, but no gauge.

What would be the best way to add a gauge? Is there a replacement sender
that would screw into same port as existing temperature switch and act as
both temperature switch and input for analogue gauge?

Or is there another way to add a block water temperature measurement?

My engine seems to be running too cold. I am planning on pulling the
thermostat and checking it's setting. If it is set too low, is there a
source for units with higher settings? We are in fresh water, so would like
to have engine run hotter - say 160F or so.

The part number for the OEM thermostat is 124770-49200 but I have not been
able to find out the temperature - I have read that it may be 120F or 140F
but that's just on web discussions.

Don't know what the setting of the existing temperature switch is either.
Anyone know?