Ok first off it's an I/O so go easy on me guys lol. Bought a 21ft 1978 centurion with a mercruiser 260 which is a 350 small block 260hp. So previous owner says it's lake ready including the impeller in the water pump. So I take it to the lake and run it 1/2 to 3/4 throttle for a couple mins watching all my gauges. All looks good. Make another lap little longer looks good. Stop at shore look for leaks and what not. Looks good. Boat is running like a bat. Surprising fast. So go out for another lap. Running around 3000 rpm (WOT RPM is claimed to be 4600) temp starts climbing hits 200 keep a close eye start heading for shore. Climbs to 220 I idle down and shut it off. Coast to the dock ( with a little swim) and call it a day. Next day I install a new impeller old one was shot. Take it back to the lake the next day and it won't start. Sounds like dead battery or starter dragging. Make a few phone calls and was advised to get it home and pull the plugs. 2 CYLINDERS WITH WATER. So I attempt to run a compression check but after checking first cylinder I notice after I let go of key about 3 seconds later starter disengages. So I look at the starter and the whole front piece is cracked. So it's pulled. Waiting to get another tomorrow. Oil Is still fresh and semi clean. No milkshake or obvious water mix. What do you guys think. Blown head gasket? Can't be sure till I run a compression check this I know. Just trying to get an idea of what's going on? Any help or ideas will be appreciated

If you were moving even a little fast as you shut it down and don't have exhaust flaps to stop the back wash water can rush in and go in the open exhaust valves. Did this once. No big deal. Change oil and run it. Continue on your path and run compression check. At this point water has seeped past the rings into the pan. If it's alot of water I had an old race guy tell me when they flipped and sank a race boat they would put a quart of diesel fuel in place of 1 quart of oil and run it a few minutes, then do another complete oil and filter change. Diesel absorbs the residual water. Heat will also help evaporate what's left.

Here's how she looks on the water

just so you know just cause water can get into the cylinders does not mean it will go into the oil, with a blown head gasket.there is a slim chance you dont need a head gasket.  its not really a big deal, to do one.  well good luck.

You want the good news, or the bad?

Be willing to bet a matching set of cold ones the manifolds are cracked internally...


Here is the lowdown.

Remove the hoses to the manifolds off the engine, there is a potential that there will be three depending on the year (you may have told me but I have the memory of a deer tick).

Now take the hoses and Chris Cross them to create a closed vessel. Now remove the hose that comes from the transom assembly and devise a fitting to pressurize the block with air (go to about 15PSI) it should hold pressure for near forever...

If you pass that test, buy some manifolds.....I am still digging to find you a descent set for "on the cheap"...

Oh and I did forget to mention that after I installed the water pump impeller I ran it in the drive way on a hose. Could my problem be self inflicted? Lol. I ran the hose for about 5 second then started it like I was told.

Was the old impeller coming apart and if so did you clean all of the debris out.