sea water in exchanger?

[Phoenix of Hamble]

Having had some work done on my engine recently, the engineer commented that he thought my heat exchanger had pretty much failed....

His reason.... "a small amount of water coming out of the overflow pipe on the fresh water circuit when the engine is run".... he seemed to think that sea water was getting in there....

Now... working on the theory that he hasn't taste tested the water to see if it really is sea water (I hope not, as the fresh water system had antifreeze in it!), and given that I also topped the fresh water up to the top just before he started work and hadn't run the engine since, it got me to thinking..

Here's my logic...... the only way that water could come out of the overflow is if it is being displaced by something..... and that could either be a] excessive pressure in the fresh water system, b] excess water from the calorifier system, or c] sea water leaking in....

For a] the only 2 real causes of this would be either a blocked/restricted exchange core, or a blown head gasket passing compression pressures into the fresh water circuit... in which case, the levels in the header tank would drop as water was displaced from the fresh water system out of the overflow... (or obviously, overheating, which it isn't....)

for b] checked by looking to see if coolant is entering the hot water system... but plausible...

for c] I can't see this happening.... the fresh water circuit is under considerably higher pressure than the sea water circuit, and so surely displacement would be in the opposite direction?... maybe the process would reverse when the engine was shut down, but that wouldn't fit with the symptoms of an overflow when the engine was running surely?

So..... my conclusion.....

I think that when I topped up the header tank just before he worked on the engine, I put the levels above its natural level, and it is just overflowing a small amount of excess water, which will stop quickly (I added about 1/4 litre of water).... it is possible that the calorifier/hot water circuit is leaking into the system, but less likely than the prior reason... on top of this, the overflow wasn't leaking at all previously so it would be quite a coincidence that it failed at the same time as my gearbox....

I can't further explore this until I get down to the boat on Friday, and run the engine for a while to see if the overflow stops, but thought i'd just share my thinking to get second opinions and see what you clever bunch of people think....

 

[pvb]

I suspect you're right - just run the engine until the overflow stops. If it doesn't stop, you have a problem....

 

[PetiteFleur]

Does your heat exchanger have rubber end caps? If so, these can become displaced and leak water from the sea water side to the fresh water side. This happened on my previous boat, I stripped it all down, cleaned up all the mating faces for the end caps, reasembled and it was OK.

 

[Phoenix of Hamble]

Thats an alternative that I hadn't thought of..... yes that is a possible mechanism for sea water to get into the cooling circuit..... and worth checking if the overflow continues after a few minutes of running.... but again I wouldn't have thought it would happen with a pressurised circuit (ie with the engine running), but actually the reverse effect?

But thanks for the replies.... it confirms that I am not going mad.... i'll talk to the engineer tomorrow, but i've been racking my brains trying to work out why it would leak sea water into the fresh water circuit while running and couldn't think of a satisfactory cause that stood up to logical consideration....

 

[Clyde_Wanderer]

The fresh water in the system will expand as it is heated and will displace any excess water which is occupying that expansion space.
If it were a car engine it would have an expansion tank, obviously because it would run hotter.
If you are talking about the water comming out of the little pipe spigot just below the filler/preasure cap, then it should stop flowing once it has purged the excess water, then everything should be hunkydory.
Keep an eye on it for a few hours when you next run up your engine, and check again after it has reached its normal working temp, then again when the engine has cooled down to see if the level has dropped to where it was before you topped it up.
I topped mine up last wk, and noticed there was a trickle comming from that pipe, but satisfied it is just finding its own level, had thougnt about fitting a small expansion tank in to prevent any water marks down the engine.
One way of testing the cyl hd gskt is to smell the coolant for signs of combustion gasses, which are very distinctive, we used to test for co2 readings by gingerly holding the exaust probe into the expansion tanks on cars, if we got a reading it meant a combustion leak into the coolant system.
Good luck.

 

[Phoenix of Hamble]

Yes, I do mean the little pipe spigot just below the pressure cap.... and your comments are exactly what I mean.... I hope that after the engine is up to temp the flow will stop... and that should confirm my (and your) diagnosis

The level had previously remained unchanged over the last 2 seasons, so the additional water was obviously not neccessary, and i'd never previously topped it up.... so that also reinforces the conclusion....

Actually.... I'm just trying to talk myself into believing the best possible cause.... /forums/images/graemlins/grin.gif

 

[TonyS]

My VP 2030 with a header tank leading to a fitting on the middle of the pressure cap also started to leak out of the PVC tube fitted to the little spigot. In my case it was that the pressure cap was slightly loose, even when fully turned. I used heavy pliers and bent the tangs so it fitted more tightly. The leak stopped and that was 2 years ago! Best of luck.

 

[StugeronSteve]

Don't stress too much. If I fill my Volvo 2020 as suggested in the manual it blows coolant off via the vent pipe until it finds its own level and stops, which seems to be just below the top of the heat exchanger casting. The green water collects in the engine bilge around the cranking battery.

If you are getting sea water in with the coolant you would experience this every time you ran the engine and not just after a top up.

Try fastening a plastic bottle to the engine compartment wall and dip the vent pipe into it, this will allow you to monitor the run off volume.

 

[Piddy]

The little pipe spigot that you mention got knocked of my Thorneycroft so prevents me from using the expansion tank as fitted (another of those awkward jobs as I can't get the filler cap fitting out). As a result, if I top the heat exchanger right up as it heats up it ejects some water onto the top of the heat exchanger from where the little pipe was.

I now keep the coolant water level a couple of inches (that much) below the top. No overheating and no water.

Cheers

 

[omega2]

Taste it, if its salty it's sea water and if it's sweet it's antifreeze, just a dab on your finger tip, not a cup full