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2007 6.0 coolant overflow

1

1rider

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After changing the coolant I have developed a problem where then the degas bottle over flows when I come down from cruise rpm. The coolant level checks out as I naturally thought I had too much in the system but I do not. Any idea what I have going on?
 
I'd suspect you didn't purge the system of the trapped air when you refilled it...until you get all the air out, the burping is likely to continue.
 
The engine manual says that the degas bottle will purge the air out as it circated while running. If it is just air wouldn't it push air or coolant out even at cruise rpm rather than just while coming back down to idle rpm?
 
Agree with Mako. When an engine is drained and refilled it is possible to get a very large bubble (several quarts) if you are not careful. I find if I pull the thermostat and fill there with a funnel until full, then replace and fill from the cap, most of the air comes out. Otherwise the exhaust manifolds seem to trap it. Do some hose squeezing as well to move the bubble.

As for purging in operation, it only happens at warmup. The liquid expands, pressure increases, and when it reaches 7 psi the cap relieves. If the air bubble has moved to the cap, then air is pushed out. If not,fluid is pushed out. Once the engine is at temperature, no more expansion takes place and it stays at 7 psi. If the cap seals correctly, when the engine cools and fluid contracts, the negative pressure will suck fluid from the overflow bottle and after a number of hot/cold cycles all the air is gone. So the first point is purging does not occur in operation except at warmup and has nothing to do with cruise rpm or idle. So what happening? Well if you have a major air bubble it is possible for the fluid to expand by the usual 8-12 oz or so and the unit still not to reach an internal pressure of 7 psi, which means there will be no purging at all. Ditto if the cap seal is bad which could allow air to be sucked back in as the unit cools. One of those two is likely your problem. So why the overflow? Don't know, maybe with more details about exactly when it happens (and when you observe it) we can take some guesses. Perhaps after coming off of cruise the thermostat closes and changes the pressure in the system near the cap and the air bubble trapped elsewhere expands, or whatever. The solution is still likely to be to get the system really full of fluid and then let the heat cycles and overflow bottle to get out the last little bit.
 
Thank you for taking the time to type a detailed explanation. To try an answer the last part of your message... The coolant comes out at about 1000-1300 rpm after being at cruise, it will not do it at all if I were to stay at idle/troll speed. It is not a large amount of coolant, maybe a 1/4-1/2 cup each time.

I believe the cap is good and I more than likely have a bunch of air in the system however, I don't know how to effectively get it out.
 
If its only happened a few times, it may take several more heat up cool off cycles to get all of the air out. leave some room in the degas bottle and see if the coolant level drops after the engine cools down...that shows some air is getting purged if you don't have a leak...
 
Mako, I have tried that and the only thing that comes out the coolant in the same way as deceived above each time. The level did drop, even to the point that I had to add coolant as I could not maintain temperature. Once added it started pushing out again when the aforementioned conditions were met.
 
That's typical of hot spotting (like when your car suddenly overheats after you stop for gas). The heat was being taken out just fine as the motor was roaring along, but when the still hot motor is idled, the heat overcomes the cooling system and ... Burlb!

Two things to check: A good raw water flow (impeller, belt not slipping, not sucking in air, etc.) If that's okay, then the exchanger will need cleaning out.

Jeff
 
I will check out raw water flow. The heat exchanger was just serviced this spring, taken out, inspected and cleaned.
 
The "hot spotting" as you come off of cruise (some sort of localized boiling in the hot areas when the coolant flow slows down) makes sense as the source of the burp. But the engines are designed to accommodate this. If your engine runs at 170 and at 7 psi pressure the boiling temp is 230 that difference is supposed to be enough to prevent boil until things stabilize. If your coolant system is not working well and operating temp is well over 170 at cruise, then that could be the problem. Or if you coolant flow is reduced too much at idle (loose belt) that could be the problem. Or if your system is not holding pressure the boiling temp will be down to 212, then that could be the problem. Or if there is a big bubble moving around from improper refill it "could" [this is kind of a stretch] allow temps to remain at 170 when cruising (high coolant flow) but immediately cause a problem when coolant flow slows (bubbles don't absorb heat). I am inclined towards one of the last two since you believe it all started when you changed coolant. The filler neck the cap goes on to is usually soft brass and can become bent just from pushing down hard while trying to get the cap back on correctly, so that is another thing to look at.
 
Cabojohn, thanks for the insightful reply. I plan to get to the boat tomorrow or at the latest Thursday to try and sort this out.
 
The bottle is/was at the full cold mark initially and then after the first two uses it so and the coolant bleed off the level actually is higher! And then it drops a little after a third usage and coolant bleed off.

the boat was new to me and based on the PO service records it was time to change out the coolant.
 
1rider said:
The bottle is/was at the full cold mark initially and then after the first two uses it so and the coolant bleed off the level actually is higher! And then it drops a little after a third usage and coolant bleed off.
Click to expand...
Sorry, I've read this three times and still don't understand what was going on with the coolant level in the degas bottle... :-(

Ok on the time for a change - just wanted to make sure there was no other known issues/symptoms that are present.
 
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