Coolant

[Farey]

I went out on the boat for 2 weeks in August, and was getting a coolant leak from the radiator cap and had to top up the water daily. At the end of the trip I replaced the cap, drained down the coolant and refilled it with an antifreeze/water mix. The coolant level seemed correct, just below the cap and and between the Max/Min level in the expansion bottle. Then I went out last weekend for 3 days, and at the end of each day the coolant level in the expansion bottle was way over Max, and over the course of 3 days several litres of coolant were ejected into the bilges. At the end of each day I checked the level and removed any excess water to take it down to the Max mark. The engine is a 16 year old Vetus M4.17.

 

I'm baffled as to what's going on?

[mickp]

Over filling and releasing excess water maybe the reason

1 minute ago, mickp said:

Over filling and releasing excess water maybe the reason

Miss read your post so ignore the overfilling comment

[Tracy D'arth]

Skin tank cooled?  May be the head gasket gassing into the cooling system.

Fresh water cooled? Heat exchanger perforated.

[ditchcrawler]

5 minutes ago, Tracy D'arth said:

Skin tank cooled?  May be the head gasket gassing into the cooling system.

Fresh water cooled? Heat exchanger perforated.

Hole in the calorifier coil?

[blackrose]

Sounds like the coolant is expanding as it gets hot and is activating the pressure cap and coming out to me! 😊

 

Used to happen on my boat even when the engine reservoir level was quite low. I just attached a rubber tube to the overflow just under the cap with a cable tie and attached the other end of the tube to a plastic bottle header tank higher up. 

 

Now, when the coolant gets hot, expands and overflows it goes into the bottle and when it cools and contracts it gets drawn back into the engine reservoir. Simples.

 

Of course, if you've had the boat for a while and it's never happened before then it's something else...🤣

Edited October 28, 2021 by blackrose

[Tracy D'arth]

11 minutes ago, ditchcrawler said:

Hole in the calorifier coil?

Good call, missed that.  Its rare but possible.

[ditchcrawler]

8 minutes ago, Tracy D'arth said:

Good call, missed that.  Its rare but possible.

From the way I read it the OP is getting more liquid every day, if so it has to come from somewhere, The hot water is pressurised

[blackrose]

7 minutes ago, ditchcrawler said:

From the way I read it the OP is getting more liquid every day, if so it has to come from somewhere, The hot water is pressurised

 

Ok I read it differently but you're probably right.

[ditchcrawler]

1 minute ago, blackrose said:

 

Ok I read it differently but you're probably right.

Only the OP knows

[Farey]

The excess water seems to be a pure mix of water and antifreeze, so I don't think it's water getting in ... and if the coolant was under presure when the engine was running, how would it?

And when it cools, the water level is also high. In response to another comment, I've had the boat for 16 years and never seen this before.

[MtB]

1 minute ago, Farey said:

The excess water seems to be a pure mix of water and antifreeze, so I don't think it's water getting in ... and if the coolant was under presure when the engine was running, how would it?

 

I agree with Tracey, this is probably a cylinder head gasket leaking combustion products into the cooling system, and the gas quite probably accumulating in the skin tank, hence the continuing need to remove coolant. 

 

You can get a test kit to check for this fault, looks for combustion products in the coolant.

 

 

 

 

[David Mack]

Have you checked there is no air in the top of the skin tank?

Depending on how the pipe runs are arranged, you could have air trapped in the top of the skin tank. As the coolant heats up this trapped air expands and pushes coolant out of the pressure cap. And once the engine has stopped running and the skin tank cools down the air contracts again, and the level of coolant in the header tank drops.

[ditchcrawler]

12 hours ago, Farey said:

The excess water seems to be a pure mix of water and antifreeze, so I don't think it's water getting in ... and if the coolant was under presure when the engine was running, how would it?

And when it cools, the water level is also high. In response to another comment, I've had the boat for 16 years and never seen this before.

You engine coolant runs at maybe 15psi and the water in your calorifier is 30-40psi. If you are gaining water its coming from somewhere, but it could be that the coolant is just being displaced by combustion gas trapped in the skin tank as above.