1990 mercruiser 4.3 bad intake manifold with pics

[al0311]

Hi guys recently pulled my intake manifold off due to an overheating issue. When I pulled them off I noticed quite a bit of rust on the inside. Looking for some advice as to what this can mean ?
I'm not to sure if the pervious owner had a leak inside but from the looks of it he did. Thanks in advance.

 

[Scott Danforth]

typical neglected boat motor.

clean it up, get good felpro gaskets, use the boat.....as in put lots of hours on it. follow the maintenance schedule

 

[alldodge]

With rust inside the intake runners the intake need to look real close at the intake if not replace it. Check your cylinders to make sure no water is in them

 

[al0311]

typical neglected boat motor.

clean it up, get good felpro gaskets, use the boat.....as in put lots of hours on it. follow the maintenance schedule

Thanks so much for the reply ! Is it usual to see rust inside those cylinder jackets like that ?

 

[Scott Danforth]

No. Its not usual

 

[tpenfield]

what do the exhaust manifolds look like?

Could be leaking valve guides . . . or the water jacket in the intake manifold is leaking

 

[al0311]

With rust inside the intake runners the intake need to look real close at the intake if not replace it. Check your cylinders to make sure no water is in them

I looked in the cylinders with a flash light I didn't see any water around the cylinders. There was some surface rust though.

 

[al0311]

what do the exhaust manifolds look like?

Could be leaking valve guides . . . or the water jacket in the intake manifold is leaking

I recently pulled the risers and the manifolds to look. The risers were rusted on the outside around the water jackets. But the inside were clean I couldn't see any cracks or rust same as with the manifolds.

 

[al0311]

So in your guys opinion I should Just clean it up real well and replace the mainfold?

 

[alldodge]

With water in the intake runners, the intake was leaking. If the leak was caused by a gasket only then the intake can be reused.

Pull the plugs (if not already) spray some fogging kind of oil in the intake runners while cranking the motor, don't use a lot just so you coat the cylinder walls. Now check compression.

 

[Bt Doctur]

And if the motor was not covered correctly water can enter thru the carb and get into the intake runners and cylinders

 

[Rick Stephens]

And if the motor was not covered correctly water can enter thru the carb and get into the intake runners and cylinders

Exactly what I was thinking about. I bought a motor that had been allowed to basically fill the cylinders with open valves with rainwater. Rusted out a couple of the cylinder walls to the point had to take 30 thou out to clean them up. All because the previous owner left the flame arrestor off and a crappy tarp covering the motor. Drip drip drip. Seems more likely than a gasket or a cracked intake.

 

[Scott Danforth]

With water in the intake runners, the intake was leaking. .

short of a really odd leak, there is no direct path between the water jacket and the intake runners. my guess is sucking moisture thru the carb, either by lightly running in super-dense fog, or by running in rain without a cover......

And if the motor was not covered correctly water can enter thru the carb and get into the intake runners and cylinders

.....or the motor was submerged

 

[scoflaw]

Them is some ugly looking heads. If it was mine, them heads would be off to the machine shop.