260 merc I/O blew head gasket after throttling down from WOT

[CaptnReinell]

Hey everyone nad thanks for reading this.

Had my boat out this Labor day weekend. Watched the Air Show and caught a couple of very small perch. previously replaced upper unit due the fact i wiped out the other one from not checking lube. Any way, got that replaced and it ran fine. Coming into port was cruising at about 25 mph then shut it down to no wake speed. soon as i did that it started missing terribly. barely got to the ramp and shifted into reverse to slow down and it quit. couldnt get it started. Got it home and pulled plugs. plugs 3,5,7 white anodes which tells me water!!!. could i have blown a head gasket by shutting down so quick (backwash from wake backing up into exhaust and quenching some hot heads after running WOT? This is a brand new motor...
any insight from all you merc gurus would defintly be appreciated.
gonna pull the top end this weekend and see what I reqally did!!

 

[Bifflefan]

Re: 260 merc I/O blew head gasket after throttling down from WOT

could i have blown a head gasket by shutting down so quick (backwash from wake backing up into exhaust and quenching some hot heads after running WOT? This is a brand new motor...
any insight from all you merc gurus would defintly be appreciated.
gonna pull the top end this weekend and see what I reqally did!!

Not likely i dont think.
Have you done a compression test to verify that it is head gasket?
More than likely if had already happened, when running at higher RPM you didnt notice, then at idle there wasnt enought motor pulling to keep it running.
Water coming in wouldnt have stopped at the valve, it would have gotten in the cylinder and locked it up.
This is my opinon and my be far from fact...

 

[TowRoper]

Re: 260 merc I/O blew head gasket after throttling down from WOT

why not do a compression test b4 taking it apart?

 

[jtybt]

Re: 260 merc I/O blew head gasket after throttling down from WOT

That's a possibility. Also if the engine died and dieseled at the end, you could have sucked water. Pull plugs and turn the engine over to expell any water. If water in cylinders squirt MMO in each cylinder and turn over a few times(with plugs out)

 

[CaptnReinell]

Re: 260 merc I/O blew head gasket after throttling down from WOT

thanks you guys for such a quick response .... I LOVE THIS SITE> it is a wealth of knowledge if you know what your looking for. I am just curious where would the water come from to clean the plugs off?? the cooling system is seperate from exhaust and intake i am still pondering....

 

[meesh]

Re: 260 merc I/O blew head gasket after throttling down from WOT

New motor you say? Are the manis and risers new? Were they checked? How about the joint between the manis and risers. Could be leaking some water back down the manifold. But since it happened while slowing down, how about your shutters, were they checked during the rebuild?

 

[CaptnReinell]

Re: 260 merc I/O blew head gasket after throttling down from WOT

New motor you say? Are the manis and risers new? Were they checked? How about the joint between the manis and risers. Could be leaking some water back down the manifold. But since it happened while slowing down, how about your shutters, were they checked during the rebuild?

are the shutters in the Y Pipe?

 

[thundercraft260]

Re: 260 merc I/O blew head gasket after throttling down from WOT

Yes the shutters are in the Y pipe.

I would suggest turning the motor over by hand with the spark plugs removed, chek for any water coming out of the cylinders then chec the compression before taking anything appart.

I had hydro lock up on my merc 260 in the spring

good luck