86’ Merc Mariner 75 HP possible seize

[Norm83]

While out and about yesterday, the motor was running great at 30 mph as usual. All of a sudden the motor started making a raw running sound. I immediately turned off the engine to inspect. After looking over it, I tried turning it back over. It wants to crank but it seems stuck/seized. It hasn’t been stripped down and rebuilt to my knowledge over the years but planned to this winter. Unfortunate but I was wondering if there would be anybody out there that may have some advice or similar experiences. Thank you in advance 

 

Norm

[L&M]

Don't rule out the lower unit. 

[Norm83]

1 hour ago, L&M said:

Don't rule out the lower unit. 

I appreciate the reply, Just hoping it’s not in the head

[lrg355]

Pull the spark plugs than see if it cranks over.  Blown head gasket or other things could cause cylinder(s) to fill with water and cause               " hydraulic lock".