Closed Cooled System - Possible Leak?

[Ray Gallagher]

I've got two mercruiser 5.7l bravo III's with freshwater closed cooling systems. Port engine exchanger is full to the brim and never has any trouble. Pull the cap off and its all still right there looking at me. Starboard is constantly at different levels. Usually when I pull off the cap there's coolant in there which then quickly drains to somewhere... no idea where but definitely somewhere. I also feel like I could fill the exchanger with 35 gallons of coolant and it would never be full... I have no idea where this stuff is going at this point. The reservoir isn't full either so I know its not going there....

Just bought the boat last year and was told there were no prior issues with it even though I know that holds no weight. Took out the spark plugs and did a compression test and no water or coolant came out so I should be good there. No coolant in the bilge and no sweet smell coming from the exhaust. These are the main areas everyone says to check, so if I can't find it there then what the hell am I missing? Probably going to start with changing the cap but I did already try switching caps with the presumably good tank and no change. Engine isn't overheating either its just something I noticed and am concerned about. Just a matter of time before I get that lovely alarm I'm sure. Who's idea was it to buy a boat??? Ah well it's still better than not having one at all!

 

[JHornsby3]

I had the same issue with our lake boat. Coolant was always MIA. Took the heat exchanger apart to flush the raw water side and replace the rubber seals. Found where the leak was. When the cooling system would build pressure, the coolant would leak out and into the raw water side. Took it in to a radiator shop and they fixed it up for about half the cost of a new one.

 

[mrsrobinson]

I had the same issue with our lake boat. Coolant was always MIA. Took the heat exchanger apart to flush the raw water side and replace the rubber seals. Found where the leak was. When the cooling system would build pressure, the coolant would leak out and into the raw water side. Took it in to a radiator shop and they fixed it up for about half the cost of a new one.

Interesting, I would never have thought of this.

In my 330DA it turned out to be the head gasket, leak down test revealed it. Oil samples may help as well.

 

[Ray Gallagher]

I had the same issue with our lake boat. Coolant was always MIA. Took the heat exchanger apart to flush the raw water side and replace the rubber seals. Found where the leak was. When the cooling system would build pressure, the coolant would leak out and into the raw water side. Took it in to a radiator shop and they fixed it up for about half the cost of a new one.

I may take a stab at this but have never done it before. Did you just already know what to do or did you follow a video somewhere? I could probably take it apart but I'd really rather follow some step by step if possible since I've never really worked on one before.

Also.. if it was going into the raw water portion wouldn't I see anything in the water around the boat? Maybe not?

 

[JHornsby3]

It was in the old maint portion of the engine manual.

Drain coolant.
Remove all hoses.
Remove end caps.
Remove and toss rubber gaskets.
Clean out really good.
Replace rubber gaskets.
Pressure check to the cap ratings.
If it leaks down, take to shop to have the core tubes replaced. They will pressure test it before they send it home.

I keep spare gaskets around somewhere in the boat stuff for that boat. They are 3" or IIRC 4" and you just trim the extra if needed.

 

[Ray Gallagher]

Interesting, I would never have thought of this.

In my 330DA it turned out to be the head gasket, leak down test revealed it. Oil samples may help as well.

Wouldn't a leaky head gasket mean coolant would be getting into the engine and would come out during the compression test?

 

[mrsrobinson]

I don't think you'd see the antifreeze in the water, but I could be wrong. I think this is one of those "where do I start first/easiest" kind of things. I would get an oil analysis to check for antifreeze in the oil. Good to have a baseline analysis anyway. At the same time I'd remove the heat exchanger and either take it to a shop to look or take off the end caps, flush it yourself, replace seals/zinc, reinstall. The problem with this is you will not be able to pressurize it. Not a bad thing to do regardless if it has not been done is a while.

 

[Ray Gallagher]

It was in the old maint portion of the engine manual.

Drain coolant.
Remove all hoses.
Remove end caps.
Remove and toss rubber gaskets.
Clean out really good.
Replace rubber gaskets.
Pressure check to the cap ratings.
If it leaks down, take to shop to have the core tubes replaced. They will pressure test it before they send it home.

I keep spare gaskets around somewhere in the boat stuff for that boat. They are 3" or IIRC 4" and you just trim the extra if needed.

Awesome thank you so much. This sounds like an end of season test though...

 

[Ray Gallagher]

I don't think you'd see the antifreeze in the water, but I could be wrong. I think this is one of those "where do I start first/easiest" kind of things. I would get an oil analysis to check for antifreeze in the oil. Good to have a baseline analysis anyway. At the sane time I'd remove the heat exchanger and either take it to a shop to look or flush it yourself, replace seals/zinc, reinstall. The problem with this is you will not be able to pressurize it. Not a bad thing to do regardless if it has not been done is a while.

Okay I'll see what the marina says too. We have a shop on site maybe I'll bring it to them if I can manage to get it off myself

 

[JHornsby3]

It's amazing how much silt and sand will get caught in there and settle. I used old inner tubes and the hose clamps to close off the hose connections. Then used the valve stem and put the pressure into the system. First the one side then the other. There was a couple tubes that would open up with the coolant side pressure but close off when the raw water side was pressurized.

 

[mrsrobinson]

Love the pups pics BTW. Malamutes or Huskies?

 

[JHornsby3]

Okay I'll see what the marina says too. We have a shop on site maybe I'll bring it to them if I can manage to get it off myself

Find a local radiator shop that does heat exchangers. Might save you some money over the marina. Boat= big money.

 

[Ray Gallagher]

Love the pups pics BTW. Malamutes or Huskies?

Thanks! Big one in the center is a malamute and the littler red one is a husky.

 

[mrsrobinson]

Thanks! Big one in the center is a malamute and the littler red one is a husky.

Very cool, I grew up with Malamutes, my parents bred them.

 

[JHornsby3]

Very cool, I grew up with Malamutes, my parents bred them.

Does that mean you like to chew on rawhide and sniff others butts? Bah duhm tiss!

 

[Ray Gallagher]

Okay I'll see what the marina says too. We have a shop on site maybe I'll bring it to them if I can manage to get it off myself

I don't think you'd see the antifreeze in the water, but I could be wrong. I think this is one of those "where do I start first/easiest" kind of things. I would get an oil analysis to check for antifreeze in the oil. Good to have a baseline analysis anyway. At the same time I'd remove the heat exchanger and either take it to a shop to look or take off the end caps, flush it yourself, replace seals/zinc, reinstall. The problem with this is you will not be able to pressurize it. Not a bad thing to do regardless if it has not been done is a while.

so there was no coolant in the oil. just changed it to be sure. the thing that is baffling me is that while the engine is shut off and i'm filling the resevoir I can never get it full. I don't think i'm "losing" coolant, I think i'm just unable to reach full capacity. I can fill and fill and it seems to just stop at 3/4 full, when i hit the fill line i hear bubbling and then right back down to 3/4 in the resevoir. Could there be a leak somewhere near the top of the exchanger? Does that even make sense?

 

[mrsrobinson]

The bubbling/gurgling is normal when flushing and refilling an empty system.

What do you mean by "unable to reach full.."? This is a closed system, at some point it's full.

Regarding antifreeze/water in the oil the only fool proof way to confirm that that I am aware of is with an oil analysis, this is who I use: https://www.blackstone-labs.com/engine-types/marine/

 

[Ray Gallagher]

The bubbling/gurgling is normal when flushing and refilling an empty system.

What do you mean by "unable to reach full.."? This is a closed system, at some point it's full.

Regarding antifreeze/water in the oil the only fool proof way to confirm that that I am aware of is with an oil analysis, this is who I use: https://www.blackstone-labs.com/engine-types/marine/

Ah I was told it would be "milky".

Regarding the coolant, when I say unable to reach full I mean that I have a 20 qt system and have dumped quite a bit more than that into it this year without even running the engine and cannot get it to stay at the fill line. I just put 4 gallons in it this last weekend even though there was already quite a bit in it and its still just floating below the fill line. I'm going to reluctantly put another 3 gallons in it this weekend just so I'm 100% certain that I myself, and not just what the marina told me, have put the full capacity amount into it before I can guarantee this statement is true. I just remember having the same issue last year. Fill and fill and fill but never full. But at the same time also never empty and the engine never overheats. Can touch the riser with my hand while its running and a temp gun as well as my gauge also showed normal operating temps. It's driving me insane

 

[JHornsby3]

Another thing to remember is that the coolant is going through the heat exchanger too. So if the is a hole in one of the tubes, the coolant can leak out that way. Meaning the coolant is escaping out the fresh water side of the system.

Just what ever you do, DO NOT use the water glass or Blue Devil system sealer in a boat. Very bad Ju Ju! Been there, done that.

 

[mrsrobinson]

Ah I was told it would be "milky".

Regarding the coolant, when I say unable to reach full I mean that I have a 20 qt system and have dumped quite a bit more than that into it this year without even running the engine and cannot get it to stay at the fill line. I just put 4 gallons in it this last weekend even though there was already quite a bit in it and its still just floating below the fill line. I'm going to reluctantly put another 3 gallons in it this weekend just so I'm 100% certain that I myself, and not just what the marina told me, have put the full capacity amount into it before I can guarantee this statement is true. I just remember having the same issue last year. Fill and fill and fill but never full. But at the same time also never empty and the engine never overheats. Can touch the riser with my hand while its running and a temp gun as well as my gauge also showed normal operating temps. It's driving me insane

I just had oil samples done on a boat I had under contract. Water and sodium showed up in them. Oil was not milky.

Before you possibly put more antifreeze in the river/creek your slipped in, and spend more $$$ for antifreeze, I suggest using fresh water to see if it will fill up on a cold engine, and stay filled up. If it does, drain/flush it then fill it up with antifreeze.