Yanmar 3GM30F Losing Water

[Forever Freedom]

We have just discovered that we are losing water through the fresh water filler cap. Additionally, the overflow sub-tank has been drained. Amateur advice in the marina is that the head gasket has gone - anyone any better ideas, or at least ideas as to where I should start looking.

[boden36]

Head gasket is a major possibility, but first check raw water flow through heat exchanger. If plenty of water coming out the exhaust, that will probably be OK. If not , then the engine may be overheating and boiling the coolant out. If the head gasket is gone, the sump oil may be milky, and there will be gas bubbles coming through your header tank, esp with the engine under load. There is a tester for combustion gas in the cooling system for petrol engines, not sure about diesels.Regards, Richard.

[Chief Engineer]

That rusty area around the cap makes me think you need a new cap.

Fill the engine up and with the cap removed....run the engine....expansion will cause a small amount to come out....you want to look for lotsa bubbles/eruption.

Do you have a water heater plumbed into the engine?

Do you have idjit lite or gauges?

[Tellie]

Idjit light. I like it Chief.
I also agree, check the cap first. Also inspect the flange the cap screws onto. Two things, one is the flange after awhile will distort and not make a proper seal even with a good cap. Second there is a gasket where the flange bolts to the heat exchanger, make sure thats in good shape as well and not the source of the leak.

[Forever Freedom]

Thanks to all for the suggestions. One of the more pragmatic live-aboards in the marina, an ex-stock car racer, reckons it is just a storm in a tea-cup and that it is only the filler cap - the engine being 18 years old. Will check out the easiest things first.