Overcooling?

[Jacob]

Hello,

I have a raw-water cooled late model atomic 4 that runs very cool (less than 120 degrees).

It has a brand new thermostat (the old one was no longer functioning), and a brand new water temp sender and gauge.
I don't think that the problem is in the guage/sender side of things, because when I shut the engine down the water temp will briefly rise up a bit to around 140 degrees.

Any thoughts on what might be causing this overcooling and/or how to fix it would be a great help.

Thanks,
Jacob

[Don Moyer]

Jacob,

There are really only three things that can cause engines to run cooler than the thermostat rating would indicate:

1) Water is getting through a partially stuck open thermostat.

2) Water is somehow getting around a properly functioning thermostat.

3) The gauge or sending unit is malfunctioning (usually the least likely).

The first two of these possibilities are sometimes aggravated by a partial restriction within the by-pass loop (between the "T" fitting in the center of the water jacket side plate and the inlet to the thermostat housing).

It's rather difficult to visually inspect the current thermostats from Westerbeke without the "breathe through" test. When looking in from the top of the thermostat, the moveable disk may appear to be down and closing off the opening in the center of the housing, when in fact, it's raised off the housing by 1/16" or so.

In terms of the second possibility, water can sometimes bypass around the base of a thermostat if the top of the head (where the thermostat seats) has eroded away to some extent. In these cases, the overcooling can be remedied by installing a spacer under the thermostat. If you find this fix to be necessary, you will need to replace the two thermostat housing studs with manifold studs. The manifold studs are slightly longer and accommodate the thickness of the spacer.

Relating again to the second possibility, water can move around the base of a properly functioning thermostat if the groove around the base of the thermostat housing is eroded away, leaving the thermostat to rise up slightly off its seat.

Best regards,

Don Moyer

[jacob]

Don,

Thanks. I'll look into those options and let you know what I find.

Jacob
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