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Old 10-14-2014, 09:48 AM   #1
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Coolant Recovery Bottle

My 8 KW Onan diesel generator has a coolant recovery bottle that fills as the coolant heats up (expansion tank). In the past, the level of the coolant in the bottle would rise about an inch and a half as the generator worked under load.

I flushed the raw water system with Barnacle Buster and since that treatment the coolant level in the bottle does not rise at all. The generator runs perfectly, the temperature sits at 176 degrees. Is this unusual or is it a good thing? I did check the level of coolant by opening the coolant cap on the generator itself and it is right up to the top.

Thanks, Howard
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Old 10-14-2014, 10:11 AM   #2
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My Westerbeke 8Kw BTD has the coolant overflow reservoir. The level does not change in mine when the generator is running. Level changing is usually a function of the pressure cap.
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Old 10-14-2014, 11:21 AM   #3
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sounds right. because it is running cooler, less expansion of coolant, hence less being forced into the expansion bottle.
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Old 10-14-2014, 11:21 AM   #4
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Sounds like your genset is running perfectly- no overflow movement and good engine temps.

On some engines, the coolant overflow does rise a bit as the coolant expands as the engine heats up. When it cools down it gets sucked back in. Your higher temperatures before acid cleaning were probably causing this and now that the exchanger is clean the temps are low enough not to force out any coolant.

No worries, Mon!!!

David
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Old 10-14-2014, 11:45 AM   #5
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Yes it sounds like you caught and fixed a hot running problem. Good job.
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Old 10-14-2014, 11:48 AM   #6
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Thanks for the replies. I will sleep better tonight.
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Old 10-14-2014, 12:44 PM   #7
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I believe the purpose of the recovery bottle is to allow the expanded fluid a place to go when hot and be held in place to be drawn back in when the system cools off, thereby keeping out air and allowing the system to stave off corrosion.

The cap has a return valve to allow suction when cooling to pull fluid back in. In the old systems when over filled it would just vent coolant out and waste it and forming an air space when cooled.

My Ford/Sabre will purge to the bilge to reach equilibrium and has no recovery tank, the genset has one and the level stays fairly constant.

I think you are good
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Old 10-14-2014, 05:21 PM   #8
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My Westerbeke expansion bottle stays perfectly stable all the time. The tiny hole to hose fitting was clogged!
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Old 10-14-2014, 06:29 PM   #9
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I would be concerned. Normally, properly operating cooling systems have no air in them. When the engine warms up and before the thermostat opens, the liquid has expanded enough to push past the radiator cap into the expansion tank. The tank may be to large to see the small amount of change. If you remove the radiator cap and then reinstall it, the tube from the overflow will drain untill it reaches the level in the reservoir tank. If you then start the engine and watch the reservoir tank as the engine warms up, you will see some air bubbles pushed into the tank from the tube. No bubbles means no discharge through the radiator cap, which isn't good.

When you see no discharge from the freshwater side of the cooling system, but the antifreeze level remains full, it could mean a leak between the freshwater and raw water in the heat exchanger. When the engine warms up, antifreeze may be pushed into the raw water side. When the engine cooles down, instead of sucking coolant from the reservoir, it may be pulling raw water through the heat exchanger, diluting your antifreeze.

Ted
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Old 10-14-2014, 09:43 PM   #10
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Quote:
Originally Posted by O C Diver View Post
I would be concerned. Normally, properly operating cooling systems have no air in them. When the engine warms up and before the thermostat opens, the liquid has expanded enough to push past the radiator cap into the expansion tank. The tank may be to large to see the small amount of change. If you remove the radiator cap and then reinstall it, the tube from the overflow will drain untill it reaches the level in the reservoir tank. If you then start the engine and watch the reservoir tank as the engine warms up, you will see some air bubbles pushed into the tank from the tube. No bubbles means no discharge through the radiator cap, which isn't good.

When you see no discharge from the freshwater side of the cooling system, but the antifreeze level remains full, it could mean a leak between the freshwater and raw water in the heat exchanger. When the engine warms up, antifreeze may be pushed into the raw water side. When the engine cooles down, instead of sucking coolant from the reservoir, it may be pulling raw water through the heat exchanger, diluting your antifreeze.

Ted
If there were a hole in the heat exchanger, the antifreeze would expand into the raw water, not past the cap.
I suspect his old antifreeze had broken down and was only as good as water and was expanding into his reservoir as it boiled over.
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Old 10-14-2014, 10:42 PM   #11
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There might be an air pocket in the cooling system somewhere that allows expansion without burping out the cap into the bottle. No big deal there.

Next time you run it, once warmed up a bit, but not hot, crack loose the cap and let it vent. When it cools down, it might draw some in from the bottle. Do this a few times and you might start seeing bottle breathe with temp cycles.

Also make sure cap and gaskets are clean.

My northern lights does the same thing, have to burp it a bit to get it to "breathe". I like the system working so just by looking at level change between hot and cold I know system is solid and tight.
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Old 10-15-2014, 03:19 PM   #12
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Today I measured the level in the recovery bottle exactly while cold. Then ran the genset and as it warmed I held the hose to the recovery bottle in my hand. As the genset reached operating temperature, the hose began to warm. After running for a bit the coolant in the bottle had gone up about an eighth of an inch. Upon cooling down it dropped back to the original level. I think it is fine. Thanks for all the input. Howard
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