Gaskets and Common Sense

[JSMoore]

Greetings,
I have a couple of simple questions for those of you with much more experience than I. First, I'll begin with the setup:

1987 Mark Twain MTC215
1987 OMC Cobra Outdrive
1987 OMC/Chevy 4.3 2bbl
Closed cooling system
Currently starts & runs great - no "operational" problems.

While I was winterizing, I discovered over-full oil, and LOTS of water contamination in the oil, (closed cooling system - no freeze yet - green antifreeze at -30*). My first thought was that the old "batwing" manifolds had finally given up the ghost. However, after having removed them and thoroughly checked them, they are fine - almost no corrosion, little to no sediment collected in the bottom - and free flowing. I also filled the water jackets in them with water and let them set for 3 or 4 days without any evidence of an internal crack leaking water into the exhaust races. Visual inspection of the heads also shows no evidence of moisture in the exhaust ports or on the spark plugs. So, I'm moving to the next area to look at.

Note: I've changed oil/filter several times and still have moderate contamination.

I want to run a compression test to see if the internal water jacket may be leaking coolant into the oil from around a cylinder. The engine won't be fired during the test - only turned over. But, I'm concerned about the brand new impeller I just installed. I also don't want to introduce water to the raw water system that I've already carefully drained.

My first question is: Is it necessary to hook the muffs up to the drive when I turn the engine over to do the compression check?

The next thing I want to do is remove the intake manifold to check the gaskets. I don't know much about the marine applications, but, in the automotive world, these 4.3L Chevy engines are famous for intake gasket leaks into the lifter valley from around the front water passages. And they sometimes do happen suddenly, just as has happened with my boat. I checked NAPA for gaskets. And, the "marine" gasket is about $35. And the "automotive" gasket is about $12. Marine is made by Victor, automotive is Felpro. They look physically the same.

Is there a difference that you can't see?

Sorry about the long post, guys. I just want to give you as much info to answer the questions as I can. Many Thanks!
JSM

 

[Bondo]

Re: Gaskets and Common Sense

Ayuh,.... You can pull the drive off, then No worries about the impeller...
If you have Water, Not antifreeze in the oil,...
Pressure testing the block won't tell you a thing...
A cracked block can't be the problem, it's full of antifreeze, Not water... Ditto the intake manifold...
And,...
A Compression test is Useless in these situations...

 

[JSMoore]

Re: Gaskets and Common Sense

Bond-o, I can't tell if the crankcase pollution is antifreeze, or not. It just looks like dirty milk shake to me. It's all emulsified. I am, however seeing condensation and "cottage cheese" inside the oil filler cap.

The only thing that has really changed is my radiator cap. I noticed the old cap wasn't holding pressure and I replaced it. Since the closed cooling system is now holding pressure, I'm getting the water contamination in the oil.

I'm kind of hanging my hat on a bad intake gasket at the front water crossover
race. I have this same 4.3L V6 in my little S10 pickup and had to replace the gasket some years ago because of water getting into the oil. The automotive gasket is a plastic/fiber gasket with a silicone bead around the various sealing surfaces. When I replaced it in the S10, the plastic/fiber had deteriorated away near the left front water passage and was allowing water to get into the lifter valley.

Which leaves the gasket..... Is there a difference, (other than cost), between a "marine" intake gasket and an "automobile" intake gasket?
Thanks!
JSM

 

[Gary H NC]

Re: Gaskets and Common Sense

Felpro has made updated gaskets for the intakes of the 4.3 and the V-8 Gm engines.
They are the Perma-Seal intake set.

Much better than the factory gaskets that crumble in your hand...

 

[zbnutcase]

Re: Gaskets and Common Sense

The problem on the auto 4.3 is the different expansion rates because they use an aluminum intake, marine is cast iron. I personally have never seen an intake gasket failure on a marine 4.3, but anything certainly is possible...

 

[Aloysius]

Re: Gaskets and Common Sense

The silicon ring style intake gaskets are notorious for leaking, esp. on v8's. they are VERY sensitive to overtorqueing. It IS the aluminum against iron expansion that's the issue, but I don't see how that's any different than the thousands of aluminum intakes for carbs that have been used for decades......

 

[JSMoore]

Re: Gaskets and Common Sense

Over torque and Aluminum vs Iron may be an issue.

However, in the case of my S10 4.3 engine, that I spoke about; it's a '91 model, "VIN Z", non-vortec motor, similar in almost every way to what's in my boat. The issue with it, (and what I suspect I'll find, when I get a chance to pull the intake on the boat), was a dried, brittle base material that the silicon ring was laid down on. The material was so degraded by heat and time, it had turned brittle, and would actually crumble to the touch in several places. Coolant, under normal radiator pressure, had blown out a small section of this base material, leaving only the silicon sealing ring behind - thus, water was seeping right down into the lifter valley and contaminating the oil.

I think it is certainly logical to think this may happen with my boat since it uses a closed cooling system, under pressure, just like an automotive engine.

From what I've been told, "early" gaskets of this type failed like that quite commonly. Since then, I'm told the gasket makers have vastly improved the material to make this "blow out" less likely to happen.

What I've been trying to find out is if there's actually a difference, besides price, between the intake gasket that is sold as a "marine" gasket and the commonly available "automotive" gasket. I know there is a difference with the head gasket. But, somewhere, I've read that there's no difference between marine and automotive gaskets except for the head gasket and possibly the exhaust manifold gasket. Any ideas on that?
Thanks!
JSM

 

[gbeltran]

Re: Gaskets and Common Sense

The marine gasket has a stainless piece to block the water passage on the rear of the heads. I know, no water actually flows across the back of the intake on those, but water does come into contact with the manifold there, that piece is there to prevent that and keep it from corroding. On a closed cooling system I cant see why you would need them.

 

[JSMoore]

Re: Gaskets and Common Sense

The marine gasket has a stainless piece to block the water passage on the rear of the heads. I know, no water actually flows across the back of the intake on those, but water does come into contact with the manifold there, that piece is there to prevent that and keep it from corroding. On a closed cooling system I cant see why you would need them.

My thoughts exactly. With a closed system, the only place you have sea water is the bottom half of the heat exchanger and the exhaust manifolds. So, I really don't know why there would NEED to be a difference in gasket materials for internal engine components.

 

[rodbolt]

Re: Gaskets and Common Sense

its a CLOSED system. if your having to keep topping it off there is a leak in the CLOSED system.
an automotive radiator pressure tester can pressureize the system to a few pounds higher than the cap rating to check for leaks without removing anything but the heat exchanger cap.