Need Help for Yanmar 18Hp locked up

[2000ModelHunter]

I just got our boat out of dry-dock new topside and bottom paint after tsunami and yesterday took her out sailing. Coming in she seized up with no warning, no over heat buzzer or warning light just shut down locked up in the bay coming in. We dropped anchor right away but drifted a bit to shallows while calling for a vessel assist. A big 52 footer there in Keehi towed us back to our slip where she's at now. I had to cut our anchor when the other captain was afraid he would hit shallows as well and wanted the tow line secured for the tow which I struggled to get both done at the same time. He got so close to us on a pass to throw us a line he hit the BBQ grill and came inches from scrapping us I had to yell at quests aboard to jump back as I thought a surf board he had tied on his stantions was going to come inside our lifelines as he passed. Very harry!

Anyway, I thought I would ask what anyone if they were me would do to see if we can get her freed up. My brother who is a mechanic on the mainland said we might pull the glow plugs and get oil on the pistons and she might be free. He said it sounded like the thermostat got stuck. Said it might be free this morning if its cooled down. There was over flow in the pan under the motor. And the overflow was low in the bottle at the top of the motor. Oil was full. And she did get real hot.

Hope someone can help.

[bljones]

Your brother is on the money as far as diagnosis. Then once you know what the problem is, you have to fix the problem. I think you're probably going to be pulling the head, which on a Yanmar is no big deal, and check the cylinder walls for scoring, but before that, if the engine will turn over, do a wet and dry compression test. If the crankshaft won't rotate, then you are going to have to yank the head at a minimum.

[MedSailor]

It does sound like you overheated, but don't miss easy and obvious stuff like catching something on the prop or a transmission issues instead of an engine one. I sucked a 12food rug into my prop and got it wrapped around the shaft once.

With the engine off put the gearbox in neutral and see if you can rotate the shaft by hand. If you can't, the bind is at the shaft/prop. If you can rotate it by hand, and the engine still won't turn over it's bound in the engine (as suspected).

Good luck.

[TQA]

If a diesel gets hot enough to seize it will stink. Pull the dipstick and smell the oil. If it smells normal look elsewhere.

Did it stop with a clonk or peter out?

Could there be something round the propshaft and preventing the gearbox going to neutral?

Can you get a spanner on the crankshaft pulley nut and try to turn the engine?

[davidpm]

On our universal 2gm the PO got the engine hot enough to stop. Forgot to open the raw water thruhull.
Let it cool down and it ran fine for another season before selling the boat.