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Understanding the raw water cooling system in an I/O

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Understanding the raw water cooling system in an I/O

Old 10-11-2018, 06:22 AM
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Default Understanding the raw water cooling system in an I/O

All,

I have a post going about my winterization and asked a question there....

I'm reposting just that question to see if I understand how the cooling system works in my Mercruiser 260.

I winterized with muffs, pretty sure the Tstat was open...I usually drain a little from the exhaust manifold and the block to see what color the AF is....didn't get to the block because it was getting dark, but the manifold was mostly water with a little AF.....

here's the re-post....


I appreciate the advice. If I understand how the systems works correctly, is it not possible that when the AF was introduced to the engine through the muffs, the thermostat was open all the way, and thus all the 5 gallons of AF went into the block...and basically none went into the exhaust manifold....or do I not understand this correctly?

Thanks again..
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Old 10-11-2018, 06:42 AM
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JoeRJGR,

First, I think some of us commented in your existing thread that introducing antifreeze into a system that already has water in it will mean it takes a lot more antifreeze and mixing for it not to be diluted. The best way is to drain existing water.

Second, its been a while since I've had an I/O boat but I am pretty sure there is always raw water running through the manifold and when your thermostats open, raw water in an open system is diverted to cool the block.

You have a whole host of problems in your original thread including not knowing whether your thermostat is working and a few of us have made several suggestions. Just because you dont like the answers you got doesn't mean a second thread is going to help
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Old 10-11-2018, 06:59 AM
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Originally Posted by mystery View Post
JoeRJGR,

First, I think some of us commented in your existing thread that introducing antifreeze into a system that already has water in it will mean it takes a lot more antifreeze and mixing for it not to be diluted. The best way is to drain existing water.

Second, its been a while since I've had an I/O boat but I am pretty sure there is always raw water running through the manifold and when your thermostats open, raw water in an open system is diverted to cool the block.

You have a whole host of problems in your original thread including not knowing whether your thermostat is working and a few of us have made several suggestions. Just because you dont like the answers you got doesn't mean a second thread is going to help
I understand the issue with the thermostat and I'll fix that problem...not worried about it now since the boats out of the water....

Also no one said I didn't like the answers I got....I appreciate everyone's advice....I'm just trying to understand how the cooling system works and why what happened to me when I tried this method did. I mentioned the dilution of the AF....

Sorry if I broke protocol or offended anyone...

Thanks for the reply...
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Old 10-11-2018, 07:18 AM
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Originally Posted by JoeRJGR View Post
I understand the issue with the thermostat and I'll fix that problem...not worried about it now since the boats out of the water....

Also no one said I didn't like the answers I got....I appreciate everyone's advice....I'm just trying to understand how the cooling system works and why what happened to me when I tried this method did. I mentioned the dilution of the AF....

Sorry if I broke protocol or offended anyone...

Thanks for the reply...
There are plenty of resources if you google to learn how an IO cooling system works

Your question about the dilution is really not specific to cooling systems, boats, etc. Its really as simple as you have something that already has a fluid in it and you are trying to add a different fluid. Its going to take a lot of the different fluid to have a higher concentration of it and force out the other fluid. Of course it can get a lot more technical than that but its really simple on the surface.

That is why best practice is to drain the cooling system before adding antifreeze. And its worth it to get the -100 antifreeze in case there is any water present that dilutes it.
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Old 10-11-2018, 12:06 PM
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Short answer, no it is not likely at all that it all went to the block.
Look up the flow diagram. On an engine full of water, if the tstat is closed, 100% flows right out the exhaust. If the tstat is open much of the new AF would make its way into the block and mix with water and head out the exhaust as some mixture of water and AF - who knows how much.

If the block is empty at the start, almost all of the AF goes to the block and only once it is full can it make its way to the exhaust.
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Old 10-11-2018, 01:40 PM
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Old 10-12-2018, 05:59 AM
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Originally Posted by JoeRJGR View Post
All,

I have a post going about my winterization and asked a question there....

I'm reposting just that question to see if I understand how the cooling system works in my Mercruiser 260.

I winterized with muffs, pretty sure the Tstat was open...I usually drain a little from the exhaust manifold and the block to see what color the AF is....didn't get to the block because it was getting dark, but the manifold was mostly water with a little AF.....

here's the re-post....


I appreciate the advice. If I understand how the systems works correctly, is it not possible that when the AF was introduced to the engine through the muffs, the thermostat was open all the way, and thus all the 5 gallons of AF went into the block...and basically none went into the exhaust manifold....or do I not understand this correctly?

Thanks again..
The statement in bold, is the issue. "Pretty sure" as far as the stat being open, will get you a good chance of a pretty surely cracked block in the spring! Because if you start with a block/heads full of water (keep in mind that this engine holds about 5 gallons of liquid) and let it idle on the water hose with cold water running in, that stat may not open enough to let much of the water out. So the AF, cannot replace the water. Unless you are very familiar with how raw water cooling works and know what to look for, there is no way to know if the stat opened far enough for long enough. With a raw water cooled open system like yours, when the stat is closed, all the AF will go out the exhaust manifolds. When the stat starts to open, some of the water in the block will exit and mix with the AF coming in via the raw water pump, but that's where your gamble is. The marinas that winterize hundreds of boats, have way of re-circulating the AF to keep it hot. Now I've been doing the manual drain and back fill with -100 routine for 15 years. I could rig up such a system as the marinas do, but I still find that manual drain and back fill is safer, less messy, wastes less expensive antifreeze, etc. You could drain the block first, then suck in the AF, but to me that is also more prone to trouble, if for some reason your impeller will not suck in the AF (it is more dense than water). Those tanks depend on gravity flow and the better way to have done it would be to add a livewell pump to pressurized the flow.
The only engines you could winterize with the AF tank, is one with closed cooling (ie equipped with a heat exchanger). Even then, you have to make sure that the AF flow in is pressurized, so the impeller does not burn up and overheat the engine.

Remember, not one engine marinizer, will tell you to winterize a raw water cooled engine, with that tank. What does that tell you? It's not right!
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Old 10-12-2018, 06:17 AM
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Fool proof way, drain everything, you're done. There won't be enough water left to make a couple of ice cubes let alone crack anything. Then you can pour some antifreeze in if you want. Different thread but you're getting the same answers. Just drain it.
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Old 10-12-2018, 06:36 AM
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Thanks everyone for your advice....I need to replace the thermostat anyway, so I'll probably drain and fill manually...if not, I'll do what I did last year...get it hot, drain....then use the muffs to circulate antifreeze....then drain again...

Thanks again!
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Old 10-12-2018, 07:06 AM
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Originally Posted by JoeRJGR View Post
Thanks everyone for your advice....I need to replace the thermostat anyway, so I'll probably drain and fill manually...if not, I'll do what I did last year...get it hot, drain....then use the muffs to circulate antifreeze....then drain again...

Thanks again!
makes zero sense "get it hot, drain....then use the muffs to circulate antifreeze....then drain again..."

what is the point?

you dont need to get it hot or add antifreeze. just drain.
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Old 10-12-2018, 08:09 AM
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If your done using the boat for the year remove the stat then flush with antifreeze. It takes me about 10 minutes to remove the two bolts hold the stat housing, remove the stat then bolting the housing back down. The gaskets for the stat are only a few bucks and I replace them when I reinstall the stat.
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Old 10-12-2018, 09:54 AM
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Originally Posted by JoeRJGR View Post
Thanks everyone for your advice....I need to replace the thermostat anyway, so I'll probably drain and fill manually...if not, I'll do what I did last year...get it hot, drain....then use the muffs to circulate antifreeze....then drain again...

Thanks again!
If you have the t'stat out already, there is no reason to use the muffs to circulate A/F. Just dump it in the block when the t'stat is already out. Then you can dump some down all of the hoses to fill the manifolds as well.
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Old 10-12-2018, 11:14 AM
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Originally Posted by JoeRJGR View Post
Thanks everyone for your advice....I need to replace the thermostat anyway, so I'll probably drain and fill manually...if not, I'll do what I did last year...get it hot, drain....then use the muffs to circulate antifreeze....then drain again...

Thanks again!
that's a waste of antifreeze. No need to do that at all, unless you want to leave it in. Drain poke the holes and you're good. I add AF only because I'm in a salt water region.
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