Merc 470 Head Gasket Failure Root Cause ?

[Rake722]

Hi all,

I am troubleshoooting or trying to identify the root cause of the head gasket failures on these engines.
an engineer friend is asking What's the core problem though - lack of heat extraction, air bubble formation due to hotspots, gasket failure, head lift?

Any info on this ? where and what is the main reason for failure ?

I am considering a copper head gasket.

Many thanks

 

[Bondo]

Ayuh,.... Bottomline Cause is most usually an overheat,....

Also the fact that it's an aluminum block, with cast iron cylinder liners, 'n a iron head,...

 

[Rake722]

Thanks Bondo, this much I was aware of but where and how does the gasket fail ?

 

[Scott Danforth]

because the aluminum expands 2 x that of cast iron. so if you go as much as 10 degrees over temp, the gasket can start to fail because the block is moving with respect to the head. and yes, the engineer that dreamed up the 470 turd should be shot. unsupported bores, iron head and aluminum block......what where they thinking

the only headgasket that works is the OEM mercruiser gasket. the copper wont work. it will create a battery with the aluminum block and dissolve the aluminum block

you can help the issue by getting an aftermarket aluminum ford 460 head and modifying it by drilling the two extra holes. this will give you a better chance of the gasket not failing.

or pull the 470 and install a 4.3

 

[kenny nunez]

As said on these posts, the whole design was not good. I have changed several of the head gaskets and when I would go to the machine shop to get the head surfaced the machinist and myself could never spot the place where the gasket leaked.

 

[stonyloam]

Three things: use the OEM head gasket, never ever let it overheat (impeller every other year), make sure you retorque the head after you bring it up to operating temperature the first time after instillation ("failure to do so will result in premature head gasket failure" from the book). Mine failed at #4 for no apparent reason, replaced, fine for last 10 years.

 

[Rake722]

Terry - the 10 years bit is reassuring. I'll do it the way you suggest if I ever need to.

I was considering an alloy head but the cost of them is just too much.

 

[2fishy4u]

It depends a lot on luck, and watching that damn temp gauge like a hawk. I just had a head gasket failure. It overheated slightly to 200 degrees before I noticed the temp rising. Happened in under 60 seconds and that was all it took. And after failure, it was smoking and smelling like coolant. You could not see where the gasket failed. One thing I learned about these engines, they really hate sea water. I have to clean the fresh water cooling system at least twice a year. (riser and H.E.) I run about 150 engine hours per year, and we spend around 500 hours a year on the water.

 

[Pocket Change]

I overheated my 1988 3.7L mercruiser when the hose under the drive came off due to a bad hose clamp. I shut it down and called Sea-Tow. I fixed it. No sign of a blown head gasket. Runs great. I put 125 hours a year on the boat. This happened 5 years ago.

 

[nola mike]

I'm wondering what I used for a HG when I replaced it 4-5 years ago. Actually had a bent valve when I had a leak into #4, which is what necessitated the HG replacement. anyway, no oem gasket for me.

 

[nola mike]

Looks like this is year 7 on a Sierra HG for me. But I remember @stoneyloam convincing me years ago that I should have gone oem

 

[stonyloam]

Yeah I got that from a hot rod site where a guy was using a 470 block for land speed trials. He said that the OEM head gasket was the only one that held up. It is not that an aftermarket head gasket will not work, heck it could last forever, it is just that it is more likely to fail in the long run. Proper assembly and keeping it from overheating are the keys.

 

[Scott Danforth]

No Title

Some of the 4-banger only guys have delusions of grandeur with the 470 block. Most come to the same realisation.....

If your going to use this motor, you need plenty of