Volvo Penta D2-55 coolent overflowing from expansion tank

[markram]

We have just finished cleaning our heat exchanger. After returning it and connecting all the pipes and wires etc, we added coolant according to the handbook - filled the heat exchanger to just below the filler opening and the expansion tank to the minimum line.
Everything was fine at lower revs up to 1600/1800 but when we got to 2200/2400 coolant started to escape from the filler cap on the expansion tank. I would think that filling the heat exchanger to top and not adding any coolant to the expansion tank would be logical but this is not what the manufacturer says. Tomorrow we will remove any excess coolant from the expansion tank and just make sure the heat exchanger is full and see how that goes. Has anybody had experience with this issue?

[Yngmar]

Check the level in the HE. If that's also full, sea-water is entering the coolant side, increasing the total level. Maybe an o-ring was forgotten or got pinched on reassembly.

Could also simply be an overfill though, although it doesn't sound like it.

[markram]

We definitely did not forget the O-rings and I am sure we put everything back together properly. Dont see how seawater could enter the unit. I will see tomorrow after we remove some of the coolant. Is there any specific way that the insert should be inserted in the unit I wonder - I dont see that making any difference?

[JEN-et-ROSS]

I don't want to be alarmist, but the issue occurring only at higher revs could indicate a blown head gasket....
I say this as we used to have an L200 4X4 pick-up that displayed exactly those symptoms and it proved to be a slowly worsening leak of combustion gasses (through a crack in the metal sealing ring that sits in the head gasket and surrounds the cylinder bore and the cylinder head) and into the water-jacket forcing coolant out via the expansion tank.................I hope it's not that..

[markram]

Unfortunately you may be right about the gasket (or a crack in the head!!) - we came to the same conclusion after checking the situation today. Next week we will do a CO2 gas test. That will give us a almost definite answer. Thanks for your input.

[santicuti]

before thinking of a serious disaster, consider that what happened to you is often normal, especially if you have a boiler on board (for hot water) also fed by the engine's coolant.
when you have reassembled everything (heat exchanger, pipes, etc) and then you have filled up with the required liquid, often, indeed always, air bubbles form in the circuit which increase its volume when hot, causing the transfer of liquid into the vent tank and, often when the bubbles are large, letting the liquid escape from the same vent.
you re-add coolant, run the engine, and you will see that after 3 or 4 boat trips the problem will be solved because the bubbles, little by little, go to the surface and come out
good wind

[JEN-et-ROSS]

before thinking of a serious disaster, consider that what happened to you is often normal, especially if you have a boiler on board (for hot water) also fed by the engine's coolant.
when you have reassembled everything (heat exchanger, pipes, etc) and then you have filled up with the required liquid, often, indeed always, air bubbles form in the circuit which increase its volume when hot, causing the transfer of liquid into the vent tank and, often when the bubbles are large, letting the liquid escape from the same vent.
you re-add coolant, run the engine, and you will see that after 3 or 4 boat trips the problem will be solved because the bubbles, little by little, go to the surface and come out
good wind

Still a problem...
  There should be no leaks between the engine coolant that heats the domestic water and the fresh (Hopefully hot) water in the calorifier.....
If there is, then you've potentially got dilute anti-freeze (Ethylene Glycol) in the domestic hot water......