What are the correct heads for 2006 Mercruiser 5.0 MPI?

juhasev

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Jul 8, 2011
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Bondo thanks for you thoughts! All this started when my impeller broke and engine overheated. Although I shut of the engine immediately the heads still cracked and I am almost 100% certain that overheating caused it. And because the engines are raw water cooled this condition can happen quite easily i.e. temporary blockage in the out drives water pickup, broken impeller etc... Therefore I am heavily leaning towards steel re-enforced seats.

The other issue I noticed was excessive wear on the seats ~ 350h. You could literally see and feel a ridge on the seats that had already formed up... Valves bound hard against the seats which makes the steel seat much better option that protects you against deforming like the cast iron. I can have my machine shop to put them in... Somebody quoted me just $60 per head to get the operation done.
 
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Bondo

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Bondo thanks for you thoughts! All this started when my impeller broke and engine overheated. Although I shut of the engine immediately the heads still cracked and I am almost 100% certain that overheating caused it. And because the engines are raw water cooled this condition can happen quite easily i.e. temporary blockage in the out drives water pickup, broken impeller etc... Therefore I am heavily leaning towards steel re-enforced seats.

The other issue I noticed was excessive wear on the seats ~ 350h. You could literally see and feel a ridge on the seats that had already formed up... Valves bound hard against the seats which makes the steel seat much better option that protects you against deforming like the cast iron. I can have my machine shop to put them in... Somebody quoted me just $60 per head to get the operation done.

Ayuh,....... can't argue the point,.... How bad are the valves,..??

That could be an indication of detonation,....

The exhaust valves are many times the 1st to show signs of it,... localized hot spots,...
 

aerobat

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Jun 1, 2011
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All this started when my impeller broke and engine overheated. Although I shut of the engine immediately the heads still cracked and I am almost 100% certain that overheating caused it.

that sounds scary. i have on my 5.0 MPI smartcraft instruments where the waterpressure is measured and a quitting impeller sould be noticed before the engine overheats - further the guardian system should kick in before engine damage occurs on a MPI. are you sure you chase the right stuff ???

i cannot help with casting numbers but could look ony my 5.0 MPI for the heads and serials if this is any help. i always believed the 260 HP 5.0 MPI have vortec heads ???
 

aerobat

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That could be an indication of detonation,....

that should not be possible since the engine features a knock sensor and retards the spark advance if detonation occours. basicly we talk with a MPI another story than on a carbed engine. thats why i,m wondering the damage with the valve seats / cracked heads due to overheating.
 

juhasev

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Jul 8, 2011
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The newer MPI engines do have a sensor that detects water pressure and I supposedly have one too. I was some 7 minutes out of the marina before I got the alarm (about to plane out) and I believe it was triggered when the thermostat finally opened and the hot water (and air) got pumped out of the engine without any replacement water coming in. So would it be possible that if you impeller quits before your engine is hot it might be possible to run with dry heads? Or maybe it just takes a few seconds to overheat the heads?

Lesson learned, change that impeller before 100 hours or may end up where I am at. I clocked in 150 hours... thinking that my bravo impeller will last as long as my alpha impeller in my old boat. Wrong! Alpha impellers located in the outdrive where they instantly get water when you start the engine. The bravo impellers are by the engine so they do run dry for a while before water is sucked in therefore wearing out more.
 
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aerobat

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So would it be possible that if you impeller quits before your engine is hot it might be possible to run with dry heads? Or maybe it just takes a few seconds to overheat the heads?

when i understand the system correctly it is possible ( on any engine ) to dry out the engine when your impeller is shot , the tstat opens and the circulating pump still works - but that means a real severe overheating , and before this happens your exhaust risers should glow from heat since they run dry long before the block /heads do.

the waterpressure alarm should trigger instantly regardless of tstat position for sure. i,ve never shot an impeller but one time running on muffs the muffs slipped off the pickup on the drive ( bravo three) and the alarm went off next second. was it not the case in your situation ?

so i,m wondering how can it happen to crack both heads by overheating that quickly when you say you shut the engine immediately .

when it comes to a solution in finding the correct heads : why do you not just call mercruiser and clarify with a engineer there what exactly heads a 2006 5.0 MPI needs ?

best regards
 
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