Volvo penta coolant - pressure test

[send54sail]

Hi there,
I've been having some coolant loss shown just by the reservoir level falling - there are no obvious signs of a coolant puddle underneath the engine but may possibly be slight signs of coolant higher up in the engine compartment, maybe from having sprayed out under pressure maybe from expansion tank or from that cap on top of the heat exchanger were the coolant comes down from the tank. Any thoughts on this? I'm guessing that either of those things leaking would be better than something wrong inside the heat exchanger?
I am thinking of getting a pressure test done but can't find any info on what that actually involves. Could anyone give a description of how a pressure test is normally done? Is it done just by running up the engine under load and looking for leaks or is it more scientific than that? I gather that car cooling systems are tested by draining the coolant and then using a compressor to force the air and to listen for leaks - is that done with boat engines too?
Also, at present the boat is out of the water and the test probably won't happen until she's back in the water - I assume that pretty much anything that could be found to need replacing/fixing in the cooling system could be done with the boat in the water? In other words, there isn't anything on the cooling side that would involve the saildrive coming out is there? Probably a silly question but I wouldn't want to pay to go back in the water and then it to turn out there's something wrong with the cooling system and the boat needed to come back out again at great expense to be dealt with.
Thanks very much in advance... its a great education reading this forum.
Cheers

 

[pvb]

Which engine is it?

Any work could be done with the boat in the water.

 

[lw395]

I found a coolant leak on a car by making a tee-adaptor and connecting a garden hose to the heater circuit.
A pressure gauge is probably a good idea, the coolant cap will be designed to vent at a certain pressure.
The trouble is, a lot of these things only leak when hot, but it is worth doing the obvious.
If you can plumb the vent from the cap to a catch bottle, it may help you spot other leaks?

The pressure is not huge 7psi comes to mind, but could be wrong.
Instead of pressurising with a hose, you could use a tyre pump.
Get the brass body from an old tyre valve and solder it into your adaptor.

It could of course be the head gasket. That's the worst case probably.
On my dodgy old car, it turned out to be the water pump.

 

[send54sail]

Which engine is it?

Any work could be done with the boat in the water.

PVB - thanks, its a D2 55C

 

[Bobc]

I had a slow loss of coolant on my engine a few years ago, with no sign of any in the bilge.

A "so called" marine engineer told me that "it must be going into the engine" and that the head gasket of heat exchanger will be knackered.

Luckily, I completely ignored him. What it turned out to be (and I suspect yours might be the same) was:-

If you take the cap off the heat exchanger, inside is a rubber seal. This was a bit knackered and worn and was letting coolant past, and the escaping coolant was evaporating on the engine. The replacement seal was about £4.

Change the seal and see how you go.