That’s pretty good.
So with a [jet boat open fresh water cooled type system, the only pump is the jet] steam pockets can form at lower temperatures (160F) than say a closed cooling system because the water pressure is lower (at idle/low rpms) thus allowing the hotter areas of the [just the head?] to boil the cooling water which will drop out minerals (or worse). Also, there is less water flow which gives a decrease in cooling water distribution and more and/or hotter hot spots. Is all that right?
How do you know 160F is the temp? And at what pressure is that at? Any other factors that could bump that temperature up or down, aluminum vs. steel heads?
How do you know most marine manufacturers (I assume jet boat open cooling system, only pump is jet) design their engines around a 140-160F thermostats?
First, the cooling requirements are almost non existent on an open cooling system at idle, there is hardly ever a case where water flow is inadequate at idle. At the same time, the horrible (for anything other than what we do) flow characteristics of an oversized gate valve flows better at low water pressure than it does at high water pressure, it's really strange how well a gate valve works.
Back to why the 160°F. Almost all manufactures for marine equipment stay well below the 150-160°F range (I can say this with 100% certainty).
There are more reasons than this for the 160 and below.
The water entering the engine is still cold as a solid bronze athletic cup. Do you really want a 100+ degree rise from cylinder 1 to cylinder 8? I don't.
On a typical jet, open cooling system, the water enters the engine at the front two cylinders.... It exits out the same two cylinders on the head. Think about that for a moment........
The only way I would ever recommend using a thermostat would be with a block mounted automotive style water pump and an I/O type thermostat housing, or closed cooling with a heat exchanger.
This makes the water temperature within the block and heads completely homogeneous. Meaning constant.
The pressure at low horsepower is less relevant that when wide open. So I think a warm idle temperature carries with it little risk.
You can challenge me all you want on the 160°F thing, I was a Mercury, Yamaha, Volvo, Caterpillar, OMC AND Marine Power master mechanic for years.
JMHO
GT
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