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Old 28-02-2010, 20:40   #31
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Is there a possibility that one of the hoses has collapsed on the inside? So when you increase RPM the internal walls suck in and reduce flow.
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Old 28-02-2010, 20:52   #32
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I apologize if this had been mentioned.

Purchase a hand held infrared temperture sensor.

I find them extremely useful for diagnosing heat/cooling problems.

Measure water temp outside boat.

Run engine.....aim at raw water hose as it exits engine...note temp differential

Aim at Freshwater in to heat exchanger and out of exchanger note temp differential

The raw water out should be close to the difference between in and out of heat exchanger.....

BTW aim at your temp sensor and expansion tank....compare with reading on Temp Gauge of engine.
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Old 28-02-2010, 21:41   #33
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Interesting thread and some interesting ideas. Here are a few points to consider:
Keep good notes on all you do. It sure helps keep things strait and keeps it a little more scientific and logical.

When troubleshooting flow, do it step by step and part by part. Look in each and every fitting and hose. Install a pressure gauge on the discharge side and as you move it along the flow path look for pressure drops indicating you just passed a restriction.

If you suspect an inlet restriction, set up a water source that bypasses the seacock, filter, etc and try that.

Nobody mentioned that you can't just crank up raw water flow to get cooling as the engine exhaust will not handle it, you develop too much back pressure. I would guess that 8 GPM is about the max that a 50-hp exhaust could clear.
 
 
If the systems seem to flow ok but it doesn’t run at the thermostat rating then the system needs fixing! 210 degrees is not OK! What you gonna do when the ambient of the seawater goes up?

The temps on the heat exchanger in/out hoses tell a lot. You should be able to hold you hand on the coolant discharge hose when the engine is running full load.

The raw water discharge should be mildly warm.

Not all new heat exchangers are built correctly! I had a similar issue and fought it for way to long. A new heat exchanger was assembled incorrectly and was replaced at no charge by the manufacturer.

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