Took our boat to a new marina for winterization and dewinterization. When dewinterizing they said we needed new riser manifolds which we had them install. we only ran the boat three times after that and the engine was acting up, it ended up blowing up. Took it back to the marina and they said we were missing a freeze plug, but didn't say there was one laying there. What are your thoughts on this? They are saying it was nothing they did but our engine was fine, never a problem with it until they messed with it.

Sounds like the block froze and push the freeze plug out, more than likely broke the block, IMO not winterized correctly

time to call a lawyer.

Agree, does sound like not winterized correctly, but you had it out 3 times, did you ever notice the temp going up or taking on water?

Salt water or fresh water ?
How old are these engines ?

Was it winterized after freezing weather set in ?

I always say you need to inspect every detail when something like this happens because you don't want to take someones opinion over a loss of your own look all your parts over and it will be evident were the damages have come from . If you take some good pictures and post them there's many sharp guys on OSO that can help you identify the trouble so you can have as accurate and detailed comment to make to the marina if need be. Best of luck to you and if we can be of any help we're here for you. Sincerely Laz Mesa

Check the oil. Is it oil colored, or chocolate milkshake colored? If milkshake, pull intake and check for cracks in block below the pushrods. Water leaking outside of engine will run the bilge pump but probably not blow engine. Crack in block will blow engine and be proof they never winterized it. I had this happen with a boat I bought. They assured me it was winterized, but block cracked in that area.

I froze an old truck once and had a freeze plug pop out almost a year later. The key word here is froze. That plug didn't wiggle out on its own.