How to fix this crack?

If you jb weld it and it doesn’t work, can you then try tig welding?

 

Seems to me you could get a sleeve or else a bolt with that fine thread and is deep or a little deeper than that hole is and put some sealer on it The good stuff and run it in there Don't kill it Just bury it and let the stuff dry and see if that will stop the oil from pushing through before you put that bolt or plug in you could put a piece of rubber I'm thinking about like tapered faucet washer type of thing that would push down in the little hole that feeds the pressure to the switch and that rubber pressing down on that hole with not a lot of pressure and some heavy duty silicone or some type of sealer to seal that up JB weld might work on the boat too but try to put a piece of rubber or something in the hole to squash down over the feed.

 

And then just leave it because this is just for a snap switch It just tells the system that there's lower no oil and if you're not using any oil checking it once a month you should be good That's what I would try to do because the oil switch threads aren't deep enough to go down in there to stop the flow down in the hole take your camera down and look inside that hole and you'll see what you need to do.

 

Bummer... My condolences to you... This will probably haunt you for a long time.

I agree that any type of welding would make a skilled welder not interested due to too many variables they can't control unless it was a stripped down block on there welding table.

It it were my problem I'd probably sand the surface to make it as perfectly round and smooth as possible to slight smaller than exact inside diameter of a soft metal pipe (not aluminum) like brass or something else and then cover everything in JB Weld and hammer the pipe on, which if done right will compress the crack and hold it together while the JB weld handles all the other aspects of it leaking.

It might not work forever, but it could...

 

Do things like that require a torque wrench?

 

JB-weld it and hope for the best. The heat cycling of the engine will probably cause it to beginning leaking in a few years. Hopefully, your circumstances will change by then.

Good Luck.....

 

Put a piece of rubber down in that hole a few millimeters thick and a long enough threaded bolt or rod to squeeze down on that rubber piece you just put in the hole You don't have to kill it with tons of torque You just want to hold the rubber against the hole It's only holding back 40 PSI coming out of a not even an 1/8-in hole