Engine bubbling?

[purplerobbie]

There is a small pipe coming off just under the radiator cap on the heat exchange for my engine. the pipe leads down into the sump under the engine which usually has some water in it. (from the stern gland and such like) Its probably got a pipe on it to stop any water going onto the alternator.

I was servicing the engine the other day and i noticed that the pipe which was sitting in the water (not a good thing) bubbled every now and then?

Why would it do that?

 

[sailorman]

the system is over pressurised, normally the head gasket is the first thing to check

 

[john_morris_uk]

the system is over pressurised, normally the head gasket is the first thing to check

Or it could just be that the fresh water has been topped up a little enthusiastically and is expanding as the engine warms up. It all depends on whether it settles down or not...?

Could be a very slow leak between the sea water side and the fresh water side. Our 2040 gushed water out of the fresh water overflow when the exhaust elbow became partially blocked.

There could be a host of things to look for before you start concluding it's the head gasket....

 

[GrahamM376]

If you've topped up the water to the top of the heat exchange, it will blow some out with expansion along with any air in the pipe. If it persists and the water level keeps dropping, you could have a weak spring in the cap so it's letting off pressure earlier or, it could be a head gasket problem.

 

[purplerobbie]

I keep thinking head gasket but it starts and runs well, no smoke or oil in the water or water in the oil. So was looking for other reasons?
Probably hoping it's not the head gasket.

 

[alahol2]

I keep thinking head gasket but it starts and runs well, no smoke or oil in the water or water in the oil. So was looking for other reasons?
Probably hoping it's not the head gasket.

If the 'outlet' pipe is under water in the bilge it may be sucking back into the engine when it cools?

 

[purplerobbie]

If the 'outlet' pipe is under water in the bilge it may be sucking back into the engine when it cools?

Thats a good point, i'll cut it a bit shorter

 

[john_morris_uk]

Or the rubber gasket in the pressure cap is cracked or perished?

Look for the simple and obvious things first before you start worrying about the head gasket...

My comment about blocked exhaust injection elbow shouldn't be dismissed. Sufficient pressure in the exhaust forces seawater back past the rubber seals on either end of the heat exchanger and causes exactly the symptoms described. (Except ours absolutely gushed out...). I've seen it on other MD20x0 engines too.

 

[vyv_cox]

I suggest you direct the overflow hose into a plastic bottle, not simply into the bilge. You can then keep an eye on the amount of water that is leaving the header tank. I have to say it sounds like normal expansion but it will help to have more accurate information.

 

[TonyBuckley]

Or the rubber gasket in the pressure cap is cracked or perished?

This was my issue with loss of header tank fluid. Replaced cap, and all sorted. Such a simple fix.

 

[scottie]

I suggest you direct the overflow hose into a plastic bottle, not simply into the bilge. You can then keep an eye on the amount of water that is leaving the header tank. I have to say it sounds like normal expansion but it will help to have more accurate information.

Try and keep the hose out of the water to prevent back syphoning

 

[stuartwineberg]

+1 although the £20 Yanmar charged for the cap was "interesting"

This was my issue with loss of header tank fluid. Replaced cap, and all sorted. Such a simple fix.