A fresh water cooled (with heat exchanger) engine should have a 180
degree thermostat. You will get better combustion efficiency, etc.

A raw water cooled (no matter if lake or sea water) should have a 135
degree thermostat. The dissolved carbonates in raw water will begin to
precipitate and foul the engine when raw water goes over about 143
deg. F. Lake water has less dissolved carbonates, so it just 'takes
longer' to foul. Of course you can run with either T'stat but will
have to 'pickle' (muriatic acid or commercial boiler descaleing
compound) the engine internals if running in raw water more often with
the 180 T'stat. ;-)



In article , OldSailor
wrote:

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?