Can water get into oil from failed exhaust parts?

[CLi87]

So I finally got my Merc 7.4 up and running and unfortunately after running it for about 20 minutes at idle on the hose I noticed my oil level was rising. I just put new head gaskets and intake manifold gaskets on so I don't think either of those are leaking. I also inspected the heads and block as best I could when I had it apart but didn't see any obvious cracks, although I'm sure there could be a micro crack somewhere that expands as the engine warms up. So before jumping straight to a an internally cracked block, I'd like to rule out everything else it could be. I have a raw water cooled system so it would be quite difficult to test, I would assume disconnect the hose from the oil cooler to the thermostat housing, and then somehow block off the risers? What would be the best way to do this and/or do they sell a block off kit of some kind or do I need to make one?

My main question is if I had a leak somewhere within the exhaust system, could that water get into the crankcase oil? I figure it would leak down into the cylinders but I don't see how water could get into the crankcase? I tried researching this but found quite a few contradicting opinions on this matter. I pulled all the plugs and they all look golden brown and the engine runs fine. I have new manifolds and risers but I re-used the original 3" extension block between them, the side toward the manifolds was smooth but the side toward the risers was a bit pitted, I cleaned it up as best as possible and used plenty of sealant with the gasket, figured it would be fine.

Another possible point of failure I had considered is the oil cooler pipe, what is the proper procedure to test it? And if this was my point of failure, shouldn't I also have water contamination in the power steering fluid?

 

[Rick Stephens]

Number one task is pull the hoses off the manifolds, plug em and pressure test the block. That is the only way to know what you have.

 

[CLi87]

Number one task is pull the hoses off the manifolds, plug em and pressure test the block. That is the only way to know what you have.

I wanted to do a pressure test of the cooling system but I couldn't figure out a good way to block off the risers?

 

[CLi87]

Also I ran the boat to operating temp on the hose and noticed quite a bit of steam and a few droplets of water coming from one of the hoses from the valve cover to the flame arrestor, is this normal just blowing out condensation or is something not right?

 

[Rick Stephens]

Steam, vapor, smoke from the vent line is not normal.

Remove all hoses from manifolds and risers, plug them with a dowel or a bolt and a clamp. Pull the line off the thermostat housing coming from the sea water pump and pressurize there - or plug that hose/fitting and pressurize at the thermostat housing. Everything but the block and water pump are then blocked out. Pressurize to 15 pounds - should hold that indefinitely.

 

[Bondo]

I wanted to do a pressure test of the cooling system but I couldn't figure out a good way to block off the risers?

Ayuh,..... You can't do the manifolds with the block,....

You've gotta isolate just the block,.....

'n No, water can't be comin' from the exhaust, when the motor's runnin',....

 

[CLi87]

Steam, vapor, smoke from the vent line is not normal.

Remove all hoses from manifolds and risers, plug them with a dowel or a bolt and a clamp. Pull the line off the thermostat housing coming from the sea water pump and pressurize there - or plug that hose/fitting and pressurize at the thermostat housing. Everything but the block and water pump are then blocked out. Pressurize to 15 pounds - should hold that indefinitely.

I can block off most of those hoses but I'm not quite understanding how to block off the risers to the Y-pipe connection? Can I actually block it off at the exhaust exit on the transom assembly?

 

[Bondo]

I can block off most of those hoses but I'm not quite understanding how to block off the risers to the Y-pipe connection? Can I actually block it off at the exhaust exit on the transom assembly?

No, block off the water hose, Before it goes into the exhaust manifolds, 'n risers,....

You want to drain, 'n pressurize, Only the block,....

 

[CLi87]

No, block off the water hose, Before it goes into the exhaust manifolds, 'n risers,....

You want to drain, 'n pressurize, Only the block,....

ooo, I see what you're saying now, and then set the engine to TDC so all valves are closed?

 

[flashback]

I don't believe there is a practical way to pressure test manifold or elbow. That test is done with acetone.

 

[flashback]

ooo, I see what you're saying now, and then set the engine to TDC so all valves are closed?

Valve position has no effect on the pressure test.

 

[Rick Stephens]

ooo, I see what you're saying now, and then set the engine to TDC so all valves are closed?

You are pressure testing cooling system - the water jackets in block and head. Nothing to do with cylinders, intake or exhaust. Goal is to totally isolate cooling system.

 

[Searay205]

In the old style manifolds the exhaust manifolds would thin right where the exhaust gases entered the exhaust manifold. You have 700F exhaust hitting 3/16" cast iron with water on the opposite side. You end up with erosion corrosion. Usually it looks like a hairline crack. I had a 3.0 liter that cracked in that fashion and in minutes I had 10 quarts in a 5 quart oil pan. When you pull the exhaust manifold look closely in all the passages for a crack or pull plugs and see if there is water on one of them

 

[Lou C]

Basically what you are doing is testing the internal cooling passages in the block, heads and intake manifold. So the hoses that go to the elbows or manifolds from the thermostat housing are removed then you take one hose and connect both sides of the stat housing, to it. Then you make up a way of supplying pressurized air to that hose which you will then cut in half in the middle of it and add a a T fitting in the center, connecting 2 halves of the hose with a gauge. This way you can find out if the head gaskets are leaking, or if there may possibly be a crack in one of the cyl heads.
Another way, perhaps a bit more complicated, is to temporarily replace the hoses that lead to the manifolds or elbows from the stat housing with clear hose. Run the engine long enough to get the thermostat open (boat has to be in the water for this test) if you see bubbles coming from the stat housing via those clear hoses, it is a sign that combustion gas is getting into the cooling water (leaky head gaskets, or cracked head).

On Chevy small blocks if it suffered a bad overheat you can have small cracks in the exhaust valve seat areas. Often these are hard to see.
I took mine to a machine shop and they found that both heads had cracks. So I wound up buying a pair of reman 4.3 cyl heads and put it back together with new gaskets and head bolts.

Other thing when assembling, the cleanliness of the parts (block deck and cyl heads) is very important, as is making sure that the cyl head bolt holes in the block are totally cleaned out (raw water cooled engines will have crud in some of those for sure) with solvent, compressed air and a thread chaser. Lastly if the head bolts are rusty, replacing is the best plan. You want clean surfaces, clean bolts and clean bolt holes to have proper clamping torque to avoid leaks.

 

[CLi87]

You are pressure testing cooling system - the water jackets in block and head. Nothing to do with cylinders, intake or exhaust. Goal is to totally isolate cooling system.

Gotcha, just want to check to see if I have this correct, I was looking at this water flow diagram for a 7.4, can I just need to block off the big hose that feeds water into the water pump and the small hose at the top of the water pump right? Shouldn't that isolate the block and heads without having to block off the hoses from the tstat?

 

[CLi87]

Duplicate post, please delete

 

[CLi87]

Basically what you are doing is testing the internal cooling passages in the block, heads and intake manifold. So the hoses that go to the elbows or manifolds from the thermostat housing are removed then you take one hose and connect both sides of the stat housing, to it. Then you make up a way of supplying pressurized air to that hose which you will then cut in half in the middle of it and add a a T fitting in the center, connecting 2 halves of the hose with a gauge. This way you can find out if the head gaskets are leaking, or if there may possibly be a crack in one of the cyl heads.
Another way, perhaps a bit more complicated, is to temporarily replace the hoses that lead to the manifolds or elbows from the stat housing with clear hose. Run the engine long enough to get the thermostat open (boat has to be in the water for this test) if you see bubbles coming from the stat housing via those clear hoses, it is a sign that combustion gas is getting into the cooling water (leaky head gaskets, or cracked head).

On Chevy small blocks if it suffered a bad overheat you can have small cracks in the exhaust valve seat areas. Often these are hard to see.
I took mine to a machine shop and they found that both heads had cracks. So I wound up buying a pair of reman 4.3 cyl heads and put it back together with new gaskets and head bolts.

Other thing when assembling, the cleanliness of the parts (block deck and cyl heads) is very important, as is making sure that the cyl head bolt holes in the block are totally cleaned out (raw water cooled engines will have crud in some of those for sure) with solvent, compressed air and a thread chaser. Lastly if the head bolts are rusty, replacing is the best plan. You want clean surfaces, clean bolts and clean bolt holes to have proper clamping torque to avoid leaks.

When I assembled the heads back together I used a wire brush to clean all the mating surfaces, put on OEM head gaskets and new head bolts with sealant already added. I used a tap to clean all the head bolt holes and followed the proper 3 stage torque procedure in the service manual. It's always possible the engine was overheated but doubtful, it only had 8 hours on it when I got it but it had been sitting for probably 25+ years.

 

[flashback]

When I assembled the heads back together I used a wire brush to clean all the mating surfaces, put on OEM head gaskets and new head bolts with sealant already added. I used a tap to clean all the head bolt holes and followed the proper 3 stage torque procedure in the service manual. It's always possible the engine was overheated but doubtful, it only had 8 hours on it when I got it but it had been sitting for probably 25+ years.

Why did you take it apart?

 

[Bondo]

Gotcha, just want to check to see if I have this correct, I was looking at this water flow diagram for a 7.4, can I just need to block off the big hose that feeds water into the water pump and the small hose at the top of the water pump right? Shouldn't that isolate the block and heads without having to block off the hoses from the tstat?

Nope,.... In yer diagram, There are 6 hoses on the t-stat housing,.....
you need to plug those 3, on the port side,........
On the starboard side, plug the 2 goin' to that manifold, 'n riser,....
Then the block is isolated,....
Take the spark plugs out, the oil cap off, open the carb,.... Drain the block,.....
To add the 15 psi of air, ya either adapt an air fittin' into one of yer hose plugs, or, you can screw an air fittin' into one of the lower block drains,....
Add air, 'n Listen,...... chase the sound of the rushin' air to the leak,....

 

[CLi87]

Why did you take it apart?

The engine had been sitting for so long that 4 valve stems were badly corroded and when I went to turn the engine over it bent 4 push rods, 3 on one head and one on the other, so I had to take both heads off to clean everything.