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Old 09-14-2016, 12:04 PM   #1
LakeErieFishing
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Default Draining engine and manifolds of water

If I remove the petcocks from the engine block, will that also drain the water from the exhaust manifolds or will I need to detach the hoses for those to drain? Engine is a Merc 888. Thanks
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Old 09-14-2016, 04:46 PM   #2
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If I remove the petcocks from the engine block, will that also drain the water from the exhaust manifolds or will I need to detach the hoses for those to drain? Engine is a Merc 888. Thanks
Should be drain plugs on the elbows that feed water into the manifolds. If not, yeah, take the hoses off, the manifolds will not typically drain through the block drains.
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Old 09-14-2016, 06:41 PM   #3
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What Dave said. Also, I'd suggest chasing out the holes with a small screw driver or a piece of wire to be sure any rust or sludge that could have bridged over the hole when the plug was in place so you're sure that everything has drained.
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Old 09-14-2016, 06:44 PM   #4
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What Dave said. Also, I'd suggest chasing out the holes with a small screw driver or a piece of wire to be sure any rust or sludge that could have bridged over the hole when the plug was in place so you're sure that everything has drained.

Oh yeah, wish I'd written that too...
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Old 09-15-2016, 10:13 AM   #5
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Oh yeah, wish I'd written that too...
Thanks - I'll do that. I also think there are brass drain plugs on the exhaust manifolds. If so I'll do the same there.

Can someone explain where the circulating water gets exited through the exhaust? By that I mean what hoses take the circulated water and discharge it into the exhaust area? In looking at a Merc 888 water cooling diagram (raw water system, NOT closed system) it appears the water is first brought into the lower thermostat, circulated to the water circulating pump on the front of the engine (circulates water throughout the engine block) and also circulated to the exhaust manifolds. Then, as the thermostat opens the water gets circulated to the risers. From there, out the exhaust(??). Can someone help clarify.

Thanks
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Old 09-15-2016, 12:30 PM   #6
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Thanks - I'll do that. I also think there are brass drain plugs on the exhaust manifolds. If so I'll do the same there.

Can someone explain where the circulating water gets exited through the exhaust? By that I mean what hoses take the circulated water and discharge it into the exhaust area? In looking at a Merc 888 water cooling diagram (raw water system, NOT closed system) it appears the water is first brought into the lower thermostat, circulated to the water circulating pump on the front of the engine (circulates water throughout the engine block) and also circulated to the exhaust manifolds. Then, as the thermostat opens the water gets circulated to the risers. From there, out the exhaust(??). Can someone help clarify.

Thanks
Basically, the system has continuous full flow from the raw water pump output to the exhaust manifolds and elbows, regardless of engine temperature. This water also has a path to go into the engine block, but it will only do so if the block is not full or the thermostat is open. The reason for the constant full flow to the exhaust system is because no matter what the engine temperature is, exhaust gases are always VERY hot and need to be mixed with cold water to prevent melting the rubber and plastic parts downstream. The outside surface of the manifolds and elbows also must remain below 200 degrees F or so per Coast Guard regulations.

The circulating pump only circulates water around inside the block and heads. When that water gets too hot, the thermostat opens and hot water escapes into the flow going toward the exhaust manifolds. This escaping water is now replaced by cold water coming from the raw water pump. As it cools the engine down, the thermostat closes to block any more water from escaping.

Eventually, the engine temperature will stabilize under a steady load and the thermostat will remain pretty stable at some opening between fully open and fully closed until the load changes.
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