7.4MPI Riser Gasket Failure

[Brianath]

I have a 2000 Mercury 7.4MPI with BravoIII drive.<br /><br />After 125 hours, the engine seized. An examination by a marine surveyor revealed that the exhaust riser gaskets had failed in both risers. There is evidence that water had been seeping in for some time.<br /><br />Has anyone else had this problem?<br /><br />What has Mercruiser done for you?

 

[Boatist]

Re: 7.4MPI Riser Gasket Failure

The gasket may have failed but more likely the exhaust manifold or riser. Exhaust minifold only last 4 to 6 years in salt water. When they start to leak water back into exhaust usually get water in back cylinders first. If water fills cylinder will rust and if try to turn over with plugs in will break something, Water does not compress like water. Sorry for your troubles, I was luckly and caught it with only one bad exhaust valve.

 

[Dhadley]

Re: 7.4MPI Riser Gasket Failure

It seems I heard of a problem with the Merc riser gaskets. I think there may have been a service bulletin out but I'm not sure. maybe one of the Mercruiser experts can tell us for sure. I would pressure check the manifolds to be sure.<br /><br />Had the motor ever been hot?<br /><br />Good luck!

 

[Brianath]

Re: 7.4MPI Riser Gasket Failure

Boat is TWO years old. Only 125 hours. I am at a Mercury Marina. Chose it so that the engine/drives would be maintained as to Mercury recommendations. <br /><br />I would have replaced the gaskets EVERY season had I known that they were questionable.<br /><br />If I end up stuck with this power plant, I will replace the gaskets every season. <br /><br />Is there anything else that routinely failes to destroy the engine/drive for the 7.4MPI/ Bravo III arrangement?<br /><br />I would like to avoid paying $5,000 to find out!

 

[russthemuss]

Re: 7.4MPI Riser Gasket Failure

Did it hot seize? No temp alarms? Ive worked on lots of boats with stuffed gaskets and blocked risers.Salt water does this to everything.Most get hard to start first if the risers are seeping.Most trouble is from overheating.I guess if your boat sits for long enough then as Boatist points out you get a water lock up and bend something.I think you were unlucky to destroy the engine from a leaking riser gasket.

 

[sea wolf]

Re: 7.4MPI Riser Gasket Failure

the problem with those gaskets is that there too thin & don't hold up. i believe merc has addressed the problem with a better gasket. when u replace them use permatex ultra black on both surfaces.