Mercruiser 5.0 manifold/risers

[Serkit]

Hello everyone first post here.

Just started getting my 2002 Maxum 2100SR ready for the summer and to my surprise something went wrong (ofcourse).

While draining oil I noticed about 3 cups of water come out before any oil, I popped all plugs out and had one cylinder pour out some rusted water as well. At this point I figured my engine was shot and I was ready to post to try to sell without an engine.

3 hours of work later I got the boat running, seafoam in every cylinder, new plugs, fresh oil and 2 battery’s. Compression test came back perfect 140-150 in every cylinder.

Now to diagnose. My first thoughts were a head gasket leak/cracked block. The compression, perfect idle, no overheat and lack of new water in oil after 2nd oil change made me think maybe neither was my issue. Now to exhaust, no idea last time these were done. They certainly need to be replaced anyway. I pulled one side(side that water poured out of cylinder) and snapped a couple of pics of risers.

My question is do you think the rust on the inside of this riser (exhaust area) is enough to say I found the issue? It’s weird to me that the rust seems to be only in this one area (where the boot sits) on the riser and there’s 0 rust on the inside of the manifold.

I will be doing acetone test on both manifolds, just wanted to get some expert opinions and maybe give me some peace of mind to dropping $1000 on a new exhaust (if maybe this isn’t the cause of the water in oil).

Thanks guys.
-Devin

 

[Scott06]

Did you get water down the carburetor during storage ?

 

[Serkit]

I really don’t think so. The boat was covered with a 600 denier tarp and the engine cover really doesn’t let in any water. If it did it would even be anywhere close to carbs.

 

[alldodge]

I have some 20 year old fresh water exhaust that don't look that bad, those have been in salt and my guess need replacing

 

[Serkit]

Yea they definitely need replacing. I’m just trying to figure out if it’s likely the problem of the water in my oil.

 

[alldodge]

Drain the block, then block off the hoses going to the exhaust manifolds. Then pressure test the block to about 15 psi

 

[Serkit]

Perfect compression test and no water in oil after oil change and running engine for 10 min on hose, you really think a cracked block is still a possibility?

 

[Lou C]

What you need to take a pic of is the manifold looking down into the center exhaust passage, if that is rusted then that's how the water got in most likely. Could be a bad gasket between the manifold and elbow, or eroded sealing surfaces. Do you have the wet joint or dry joint exhaust? Keep in mind if used in salt water cast iron exhaust needs to be inspected and most likely replaced at 5-7 years of use to be on the safe side.

 

[Serkit]

Wet, no visible rust in the manifold.

 

[achris]

Wet, no visible rust in the manifold.

The rust referred to is internal. You need to pull both elbows off, and using a large screwdriver, see if you can punch a hole from the exhaust chamber into the water passage at the top of the elbow (obviously the elbow is inverter when you try to do this). If you can punch a hole, they need replacing. If the passage is fine, clean up the gasket surfaces with fine emery and examine them CLOSELY. The metal between the water jacket and the exhaust cavity should not be eroded, and should be clean and bright. If you see any 'dull grey' in the metal, that's the beginnings of the jacket failing and water passing....

Chris.......

 

[Serkit]

The rust referred to is internal. You need to pull both elbows off, and using a large screwdriver, see if you can punch a hole from the exhaust chamber into the water passage at the top of the elbow (obviously the elbow is inverter when you try to do this). If you can punch a hole, they need replacing. If the passage is fine, clean up the gasket surfaces with fine emery and examine them CLOSELY. The metal between the water jacket and the exhaust cavity should not be eroded, and should be clean and bright. If you see any 'dull grey' in the metal, that's the beginnings of the jacket failing and water passing....

Chris.......

Thanks chris, Im not able to punch a hole but the risers are definitely shot. the entire top water jacket is completely rusted shut. Also there are huge "rust balls"? not sure what to call them that can be seen from the gasket end in the jackets.

The manifold and risers have been ordered, got a pretty good deal on sierra kit for $550 shipped.

My main concern is if i can make an educated guess that the water in the oil was caused by an exhaust problem. Is the internal rust seen on the first picture posted enough to say water was inside the exhaust chamber and therefore theres a good chance some leaked down.

 

[achris]

.... Is the internal rust seen on the first picture posted enough to say water was inside the exhaust chamber and therefore theres a good chance some leaked down.

No. Rust at that end is normal. What we need to see is the (cleaned) gasket surfaces of the elbows and manifolds.

Chris.......

 

[Serkit]

10/4 will do tomorrow thanks chris