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1989 351 58 OMC Lots of Water in Oil

phillipjf16

New member
"Hello everyone,

I have a v


"Hello everyone,

I have a very stubborn 351W getting a lot of water in the oil.

Heres what I've done so far in an attempt to fix the problem:

1)New Exhaust Risers
2)Pressure tested Exhaust manifolds - Passed
3)Removed intake and inspected lifter valley for cracks - Didn't see any visible cracks.
4)Removed water pump and with intake removed, pressure tested block/heads. Pressurized one side at a time via the water pump ports - Passed, held air pressure for 4 min before disconnecting.
5)New intake gasket and bolts.
6)Compression tested all 8 cylinders. All were around 130-145

Just went out on the water today and the problem was not even slowed. I'm still getting a LOT of water in the oil. Level on dipstick rises about a half inch every few minutes with constant WOT.

The only thing I can think of that hasn't been confirmed is a crack in the intake manifold.

When I removed the intake I took a look at the bottom of it and everything seemed fine.

Does it seem feasible that this amount of water could spray into the lifter valley through a crack in the intake and eventually down to the oil pan?

Is there a way to pressure test the intake with it still attached to the engine?

Any input or experience with this would be a huge help.

Thanks!

- Phil"
 
From what you've said it&#

From what you've said it's hard not to be suspicious of the intake or it's gasket surfaces. Did you inspect thoroughly for corrosion at the sealing surfaces where the intake meets the heads?
When I replaced the intake on my 1990 4.3L (carb change) a couple of years ago I noticed quite a bit of corrosion in the water inlet. Closer inspection revealed very thin remaining metal on the bottom of it. It was just a matter of time till failure.
 
[i]Is there a way to pressure

Is there a way to pressure test the intake with it still attached to the engine?

The only valid way to pressure test anything is with the intake still attached imho.

Pressure test should've been step one.

To pressure test:
1. remove water lines to manifolds and plug them off with 5/8" bolts and clamps
2. remove the hose that brings water from the drive to the thermostat hsg and pump 10 to 15 psi air pressure in. (still connected to tstat hsg.)
3. listen for the hissing.

^^ everything assumes RWC
 
"Thank you guys,

I'll h


"Thank you guys,

I'll have the manifold tested first thing tomorrow.

I do have another question that I was hoping I could get some insight on:

292006.jpg
OMC351"">

The 2 coolant ports between the heads and the intake circled in red above...

Are they supposed to be open in the intake and allow water to flow into the intake?

When I removed the intake these ports were blocked off... I'm not sure if it is supposed to be that way so I just wanted to check."
 
Should be blocked. Are you sur

Should be blocked. Are you sure you are getting water to that port side exhaust manifold? Looks like it's been a little hot.
 
"Chuck,

It does look quite


"Chuck,

It does look quite different from the starboard side. I believe that is because the previous owner replaced it at some point and the replacement manifold was not painted, so its become slightly oxidized unlike the painted one on the port side.

- Phil"
 
"I just remembered another thi

"I just remembered another thing that may be of help...

After running the engine at 3-4k RPM for a few minutes. When we stopped and I took the engine cowling off to listen for any abnormal sounds, I heard a gurgling / hissing noise from around the water inlet area on the intake.

I obviously couldn't pinpoint where it was coming from but it sounded like it was coming from the front area of the intake.

- Phil"
 
"After sitting and contemplati

"After sitting and contemplating this issue for a few hours now... I'm beginning to make sense of what is happening in the engine.

I do know that, at speed, there is quite a bit of white smoke coming out of the exhaust.
I know that water is not entering the cylinders from the exhaust.
I know that the compression test looked good, so it is not a head gasket or crack in the head.
I did not see any external cracks in the lifter valley on the heads or block, or on the underside of the intake.

My conclusion:

Cracked intake manifold in an internal water passage, letting water get into the intake runners, and then down to the cylinders. Then past the rings and down to the oil.

I've never experienced this before but I'm counting on it being a very real possibility.

Thanks,

- Phil"
 
"Not that I know of..

I jus


"Not that I know of..

I just completed the test Hy Stat instructed me to do above...

I pressurized the system to 20psi and it held for a few minutes... but the entire time I could hear water dripping down into the oil pan.

Finally, after the pressure pushed all the water out, I could hear hissing. I tried listening from all sides and angles of the engine and the noise stayed fairly constant, as though it was not localized to one specific section but near the middle.

After a while of watching the pressure drop and listening to the hissing from all angles, I removed the intake and this is what I found?

292085.jpg
Top End"">

Any thoughts? Is it most likely my intake? Why is there so much water around those ports in the middle of the heads?

Thanks for any input!

-
Phil"
 
Can't tell for sure in the

Can't tell for sure in the picture but there appears to be a lot of corrossion around the center water ports on those heads. They don't look flat. Is that the case?
 
"Phil, looks to be a sealing p

"Phil, looks to be a sealing problem, What you could do is clean the heads of any gasket material and use a straight edge to verify that the head surfaces are flat, also clean the intake and do the same thing looking carefully at the center ports on the heads and intake areas. If intake is not true an aftermarket intake from Edelbrock is a direct bolton and will work fine. Also Mr. Gasket made extra thick intake gaskets at one time.If its the heads,well try the thick gaskets or pull the heads to have them milled a couple thousands, NO FUN!"
 
"Thanks gentlemen! I'll be

"Thanks gentlemen! I'll be removing the heads and having them cleaned and inspected for cracks and trueness. I have to do this anyway if it is a cracked block and since I want to reuse my marine cylinder heads on a new block anyways, I'll need to make sure they are in good shape.

I'll keep you updated."
 
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