VP 2003 coolant mystery

[Sans Bateau]

Last year I notice some green coolant mix in the bottom of the shallow bilge below the engine. A thorough search found no leak. I assumed that I had overfilled the header tank which was full to the top.

Twice since I have found coolant in the bilge. After a hard motor, earlier this year, a lot of it. On all occasions the header tank has remained full and there is no overheating. There is evidence that the coolant has been leaking from the filler cap.

I did suspect at first that water in the calorifier might be forcing back through a small hole into the circulation system, but I have tried with the electric heater on and the bypass valve is working, so no over pressure there. The engine starts easily and runs fine, so I don't suspect a head gasket.

So what is making the coolant leak, and where is the 'top up' coming from? Is it possible that when the engine gets hot excess water is expelled from the header, then as the engine cools, and as the coolant shrinking produces a vacuum which in turn is drawing seawater in through the joint between freshwater and seawater sides in the heat exchanger?

 

[cpedw]

I have had cooling problems with a VP 2003. A possible explanation of your trouble could be a leak from the seawater to the freshwater in the heat exchanger. This may be down to high seawater pressure int he heat exchanger because of fouling in the exhaust mixing elbow restricting the flow of seawater.
I surmise this as the exhaust elbow is a common source of trouble and in investigating my problems, the assembly of pipes and seals on the heat exchanger struck me as quaint and relying on a lot of good luck. It turned out that my problem was shellfish growth in the seawater inlet - not likely to be your problem.

Derek

 

[mohawk29]

Im having the same problem with one of my AD41's. My mechanic is very puzzled.

 

[wotayottie]

My 2003 is raw water cooled so I have no direct experience of your problem.. But assuming that the engine freshwater cooling system is pressurised in the usual way, then I cannot see any way that sea water could get in during a run. The pressure of the hot cooling system should always be way more than that of the salt water flow through the heat exchanger.

Pressures great enough to force water out of the engine cooling system are oil pressure, combustion gasses or the cooling system boiling. Gasses would leave the system short of fluid after it had cooled and you say this isnt the case. Same with boiling. And a leak between the oil system and the hot water cooling would show up with emulsified creamy coloured oilin the sump.

So my bet is still on the hot water system. That system is pressurised and if the pressure is similar to that of the engine freshwater cooling, fresh water would only flow from the calorifer into the engine cooling system as the latter cooled down. Just suppose that you not only had such a leak but that the pressure in your engine cooling system was low because of a tired pressure cap. Engine heats up, and water is initially expelled from the pressure cap into the bilge because the pressure cap blows off below the operating pressure in the calorifier. . As the engine cools, pressure in the cooling system drops and the system is topped up out of the fresh water in the calorifier.

Just a theory but in your case I would disconnect the calorifier and give the engine a good run to see if the problem went away.

 

[Sans Bateau]

You certainly have a good understanding of my problem and you are thinking along the very same lines as me.

Stick with your theory, but ignore the hot water system, I'm favouring the 'top up' water being drawn in from the sea water side as the engine cools.

 

[MoodySabre]

If you had a hygrometer (or what ever they are called) you could test the specific gravity of the coolant over a period and see if it is diluting.

Just an idea - I know nothing really /forums/images/graemlins/smile.gif

 

[wotayottie]

[ QUOTE ]
You certainly have a good understanding of my problem and you are thinking along the very same lines as me.

Stick with your theory, but ignore the hot water system, I'm favouring the 'top up' water being drawn in from the sea water side as the engine cools.

[/ QUOTE ]

Yes the fresh water system could suck in the raw water through a leak / hole as it cools, but in that situation the fresh water would leak out through the same hole when the engine is hot and running, not into the bilges. The pressure cap on the cooling system ought to be something like 5 to 10 psi and there's no way that the raw water will be under that pressure.

Now I guess that the hot water in the calorifier could well be at that sort of pressure and that pressure will be maintained after you leave the boat and whilst the engine is cooling - provided you havent run the tap after switching off the leccy.

But all this is theory. You need to start eliminating possibilities and the easiest one to start with is the calorifier since just bypassing this with a short length of hose will prove it one way or another.

 

[Sans Bateau]

[ QUOTE ]
But all this is theory. You need to start eliminating possibilities and the easiest one to start with is the calorifier since just bypassing this with a short length of hose will prove it one way or another.

[/ QUOTE ]

Last weekend with the boat out of the water I left the immersion heater switched on. After a while we got water dripping from the pipe that runs from the pressure release valve on the calorifier. Question is what pressure do they work at?