VP 5.0 GXi-G spark plug corrosion

1994almeida

Petty Officer 2nd Class
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Mar 29, 2006
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125
Hello.
This spark plug for cylinder #8 (front right cylinder) shows signs of corrosion.
The other spark plugs are ok.
Will I have a water inlet just for this cylinder?
The exhaust manifolds are only 2 years old.
What other situation can cause water to enter a cylinder?
Thanks
Spark   8 b.jpg

Spark 8 a.jpg
 

Lou C

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Nov 10, 2002
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It all depends on where the water settles in the exhaust manifold. You can have a small leak between the manifold and the elbow and depending on the angle of the boat it may run to the same cyl. Other causes are water leaking into the carb or throttle body, or a leaky cyl head gasket.
I would get on that ASAP, water in cyls is not good, especially if it sets up over the winter.
 

1994almeida

Petty Officer 2nd Class
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Mar 29, 2006
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125
Thanks.
I saw the distributor cap and got confused.
Is the front right (starboard side) cylinder
IMG_20220309_150942 Distrib.jpg
 

alldodge

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Right side facing the bow at the stern is starboard, other side port (left)

You have an I/O so the front of the motor faces the bow. If you had a V-drive (inboard) the front of the motor would face the stern. Everything is referenced from the orientation of the boat, not the motor
 

QBhoy

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How certain are we that what is shown there is corrosion? Could it be carbon?
 

Lou C

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I think carbon would be black there’s a lot of red in that build up on the plug.
The crab cap makes the plug identification confusing.

That build up looks like that water has been there for a while. When I had my blown HGs it wasn’t that much at all. Just a little rust & an orange cast to the center insulator.
 
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cptbill

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Oct 6, 2012
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638
Yep, got water getting in there so start looking at manifolds, risers, head gasket, cylinder head
 

1994almeida

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When starting the engine, it shakes. After starting, the engine works fine. Of the eight spark plugs, only one was bad. The sparks look like metal.
 

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Lou C

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Volvo Penta had a lot of trouble with the gaskets on these and they were revised a couple of times. Do you know if whoever installed them used the latest style gaskets and followed VP's instructions?VP manifold  and elbow instructions.jpgvolvo exhaust instructions 2.jpgVP new syle riser gaskets.jpg
 
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Lou C

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My OMC engine has the same style exhaust, it is Barr aftermarket. I used their gaskets coated with Permatex Aviation sealer and had no leaks at all. Still good 5 seasons later.
 

QBhoy

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Surely if it was a manifold issue…more than one unit would be affected..usually, you’d think. I think that’s more an ignition issue from the usual source of such a thing…the cap !
 

Lou C

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Perhaps misfiring, and those are fuel deposits? Or perhaps a leaky valve seal?
Another modern "improvement" that crab cap. I had GM cars with both the old points ignition (1972 Chevy Impala 350) and the later HEI system (1975 Olds Delta 350) and neither one had problems with the standard Delco caps. Same with my old boat, I find that I usually get 5-6 seasons from a set of points, whereas in the old days we used to change them yearly as a matter of course.
I actually prefer stone age systems, points and carbs, I can diagnose and fix them easily, and no electronic mystery boxes, chasing bad connections, etc.
 

stresspoint

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I'm guessing but not an xsput opinion :) ,the inlet manifold is leaking from the crossover into the intake runner.
check you have no sign of condensation in the oil filler cap .
pressure test the motor.
wherever its getting in from ,get onto it ASAP as water in the cylinders never ends well .
 
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Scott Danforth

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I'm guessing but not an xsput opinion :) ,the inlet manifold is leaking from the crossover into the intake runner.
check you have no sign of condensation in the oil filler cap .
pressure test the motor.
wherever its getting in from ,get onto it ASAP as water in the cylinders never ends well .
may be common on the 4.3, however nearly never happens on the 5.0 or 5.7
 

QBhoy

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My money on an ignition issue from the cap. Or a bad plug. Scary to mention, but there was a huge amount of these iridium plugs that were counterfeit and went worldwide from china. Caused all sorts of issues. Ngk actually released a guide on how to spot a fake. That’s how bad it was.
 

cptbill

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Start simple, pull that exhaust manifold and and check there first a lot of times you can even see a small crack in head that way. If it's the same cylinder all the time I would not be surprised if there was a small crack in that head
 

Bt Doctur

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Definitely rusted, being only just 1 cylinder I`d be looking at the exaust valve area in the head for a crack. Only seen when the valve is removed,and valve should also show signs of rust
 
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