6CTA pushing anti-freeze into over flow bottle?

[dnord2]

I recently had my coolant system apart, refilled it and now I push coolant into the overflow bottle. Whats weird is that is rises when running, then comes back down once the motor is cool. The other engine, the level in the overflow bottle never changes. Also seems to run 10 degrees warmer with this new situation. Is there a way to bleed the coolant system, air bubble causing that maybe?

On this picture, the bottom line is where the coolant sits while cold, and the upper line is where it ends up hot. And the hot line realistically is an inch higher than that.

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[dnord2]

Thank you for the thorough response, I often wondered why you had to bleed a system when there is a small relief tube going from the radiator cap to the overflow bottle, seems like that would be self bleeding by design.

Anyway, the PORT engine is the one that rises and falls with engine temp. Last time out, I idled out at 1200 with the cap off. Right away the AF was being pushed out the cap slightly, just a constant dribble. I let it go to 170, then capped it off. What I thought was weird, was that the Starboard motor (the one where the coolant level stays relatively flat in the overflow tank), I took the cap off that one too during warm up, and that one WAS NOT dribbling out AF on the way out.

Starboard engine runs about 165-170, Port motor runs slightly warmer at about 175. I put 200 miles on the boat this weekend, maybe thats just where they like to run.

Thanks for the responses.

[Clark Leighs]

Which engine shows the coolant overflow bottle rising and falling. Doesn’t really matter a lot but THAT engine is doing exactly what it is supposed to do. As the engine warms the coolant expands and the cap releases some coolant to the bottle.. As the engine cools the coolant shrinks and the caps SECOND valve,
[ a vacuum valve] allows the engine to pull back the previously expelled coolant.. This means also that the engine is as full of coolant as it can be which is good, no air inside. By monitoring those level changes you can tell if things are working properly.
If that level stops rising and falling then start looking for a loose hose clamp, a bad pressure cap, a dirty pressure cap sealing area.

It is the other engine where the coolant level does not change that could be the problem. If all is well meaning NO leaks, the system is actually full, the cap is the correct one meaning a coolant recovery type and it too is working then the level should change also. Try adding some coolant to the system to the bottom of the filler neck and reinstall the cap. Add about 1″ of coolant to the bottle and then the next run if it does not start to do the same rise and fall then that engine may have a problem. Upon cooldown the engine may pull ALL of the bottle side coolant back and empty the bottle. It may need some adjustment of the coolant level, AT THE BOTTLE, to get working properly. Just look for the rise and fall. Once set up properly and the fill/empty cycle is working adjust so about 1″ remains always. It could take a couple of run cycles to completely fill the system. This rise/fall cycling will purge the engine of any air but it must be FULL to work.

This will ensure no air is inside the engine, that the engine is as full as it can be.

And be absolutely positive that all connections and clamps are tight. Even small looseness causing a tiny leak which will defeat these systems.

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Tony Athens

[dnord2]

Thanks Bill, good idea I’ll try that. (since swapping the intercoolers took the better part of my morning lol) this would have been easier.

Im also going to let it warm up with the cap off, to push some air out if there is any.

Thanks-

[Bill Stenger]

Most likely a bad cap. Swap caps and see if your issue moves from one engine to the other. The coolant appears to be clean. The other culprit is exhaust pressure in coolant. Which generally makes the coolant dark with soot. Try the caps first.

[Author]

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