Tohatsu / mercury 3 cyl water on plugs.

[ice_spy]

I have a tohatsu md50, 2003 3 cyclinder. Motor was running fine for approx 3 hrs then blew a head gasket. Possible cause was a blocked thermostat with a bit of plastic lodged in there.
Gutted thermostat, skimmed head approx 6thou and skimmed deck / black approx 10 thou. Only enough to flatten the surface areas.
Motor has little to no corrosion. No pitted edges on flat surfaces.
Replaced two head gaskets now, torqued properly to spec stamped on head. 18 ft pound.
New bolts installed.

Again tested today with new gasket and still plugs coming out milky. Dropped in the water for quick run and no power due to water in cyclinders. Definitely leaking, not just moisture in the block.

The only thing I can think of now is that the gaskets used are non genuine and maybe not sealing as good as original gaskets?
Base gasket has been replaced but power head pulled on off 3 times, gasket still looks ok nice and thick with no tears but maybe this is not sealing and somehow ingress water through the base plate gasket?
I don't know what else to do, my boat is out of action until I can get this water leak fixed. The head looked good with no signs of cracks, although I have not pressure tested the head. Could the exhaust ports cooling plate be leaking somehow?
I was under the impression that only a head gasket would allow water in the cyclinders not a base gasket or side cover exhaust plate gasket.

Any help or suggestions would be most appreciated, I can not afford to keep buying head gaskets and now I don't even know for sure what it is. The only option I thought was to replace the head gasket with genuine and try again.

[Fast Fred]

look at the bace gasket, and exhaust cover gaskets. i'd pull exhaust covers have a look in there. right after i checked the fuel tank to see if any water in fuel.

[ice_spy]

No water in fuel, so it's possible if the side cover exhaust plate gasket has failed this could allow water in the cyclinders ? Also if the base gasket failed this could also allow water in the cyclinders? I will check the exhaust plate cover side plate gasket 1st and see what I find.
Thanks Fred.

[Fast Fred]

yes, ether of those could leak and wet it out, exhaust is easiest so go there first, should be a tell tale spot were it's leakin in.

[ice_spy]

I really appreciate your advice to help me. So far no one else can/ has. Even marine workshops.
Could I do a compression test to attain if the head gasket has failed again or if not the water then must be coming in from somewhere else ? Like the exhaust post cover.

[Fast Fred]

yes, you could comp' test it. that will let you know the head gasket is sealed up, and the leak is one of the other two. then pull the exhaust covers see what you can see.