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post #1 of 4 Old 05-13-2009 Thread Starter
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Flushing a raw water diesel

I have a Yanmar 2GM and have installed a connection to flush the raw water cooling circuit with a hose before shutting it down. The fitting is installed between the thru hull and the strainer. While the motor is running, I turn the hose on about a quarter turn and then close the raw water intake. I watch the exhaust, and the coolant exiting the boat looks normal. Can I do any damage by having too much pressure in the fresh water hose? I assume the thermostat will prevent this from happening. Is this correct? I tried flushing the motor with the top of the strainer off, but got an air pocket in the system the next time I started the motor. I could also turn the pressure in the hose up with the intake open allowing any excess pressure to exit through the intake. Thoughts?
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post #2 of 4 Old 05-13-2009
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I would NOT use fully pressurized shore water as a coolant on ANY engine. Too much water pressure could force water into the oil or back flow from the exhaust to the pistons (neither of which is good).
I use a 5 gal. bucket that I tap into the cooling water supply and let the FW pump pull in the water it needs at its own rate. If you want to run more then 5 gals. into the engine then just stick the hose into the bucket with a low enough setting so the 5 gal. bucket does not overflow.

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post #3 of 4 Old 05-13-2009
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I agree with Caleb about not pressurizing the engine cooling passages with full water pressure. I some areas this can be in excess of 100 psig. A pressure regulator would be ideal but just using a manual valve to throttle the flow would be OK. Also, make sure you shut off the water and then stop the engine. Leaving the water on with the engine stopped can back water up from the exhaust into the engine cylinders.
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post #4 of 4 Old 05-14-2009 Thread Starter
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How do you prime the hose between the bucket and the raw water hose. I guess I could leave the raw water intake open, let the sea water back flow into the bucket, then shut the intake. Otherwise, won't I get an air lock in the system?
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