Cracked Exhaust Manifolds - what else to check?

[rtflew]

Had an overheating issue related to a way to old impeller last weekend, and went through the lower unit replacing water pump & impeller. That issue is solved. Replaced thermostat and lower unit lube while in there.

Now, I clearly have cracked exhaust manifolds from the overheating issue. I can see the crack on the outside, and water sprays out of the crack (on the outside edge or each) when boat is running on Muffs (so I know the impeller works - um, yippee?). So from researching that, those definitely need replacing.

As this is my first foray into marine exhaust diagnosis, repair & replacement, what else should I be looking for after an over-heat? Any experience & knowledge is appreciated.

Boat: 1990 Bayliner 2050 w/ 4.3L Merc & Alpha1 (gen1)

My list so far:
- There is another leak downstream in the exhaust - water is leaking out behind the engine, and coming out the back of the boat around the stern drive (but not out with the exhaust thru the prop). No idea where that is coming from yet.
- Water is also leaking just after the exhaust elbows at the 90-degree bend hoses - I assume there is some sort of anti-backflow flap in there that may have melted?
- Would the exhaust bellows (whatever those are - haven't torn it apart yet) likely be melted?
- Sounds like I need to test to ensure the heads have not blown a gasket - the oil does look good, no sign of milkyness or water in it. Do I still need to pull plugs & turn over engine to see if water comes out? Do I need to run a compression test?
- Is it possible / likely that if the manifolds are cracked that the heads or block are cracked as well? (hoping that is not the case)

What else do I need to be checking for?

Do I need to pull the entire outdrive (upper & lower portions) off to get to everything? Can I get to everything without pulling the motor? (I don't have an engine hoist, so hoping I don't need to go that far)

Sorry for all the questions, wanted to confirm for my scenario after reading up on the archives as much as possible.

If the heads & block are cracked, my next thread may be about engine swaps to a merc 5.0 or 5.7 from the 4.3, but we'll wait off on that for now - $500-$1000 for new exhaust manifolds & some downstream parts isn't enough to make that decision yet.

Thanks in advance for your help!

RT

 

[rtflew]

Re: Cracked Exhaust Manifolds - what else to check?

Forgot one other question!

I can find diagrams of the exhaust manifolds & elbows, but haven't been able to find parts diagrams & breakdown of the rest of the exhaust system to the sterndrive. Any suggestions?

My Seloc repair manual only shows for other engines, no pics or diagrams of my actual engine (ugh).

Thanks!

RT

 

[rtflew]

Re: Cracked Exhaust Manifolds - what else to check?

I did track down in the manual I downloaded yesterday the exhaust diagram finally (pages 415-422), so at least I have that now, too, to guide me on the exhaust.

If I can just figure out if I need to just pull the whole exhaust now (can it be done w/ engine and/or stern drive being left in place?), and what else I need to investigate (heads, block, ???).

Thanks!

RT

 

[zbnutcase]

Re: Cracked Exhaust Manifolds - what else to check?

In 23+yrs, I have yet to see exhaust manifolds cracked from overheating. You SURE it wasn't frozen? If so, expect a cracked block as well.

 

[rtflew]

Re: Cracked Exhaust Manifolds - what else to check?

That is a good point - if the impeller melted last year before or during winterization, it's very possible the antifreeze didn't get where it needed to be...

So to test for cracked block, do I turn it over w/o plugs and look for water to spew out? Or do a compression test? Or some other test?

 

[jtmarten]

Re: Cracked Exhaust Manifolds - what else to check?

My list so far:
- There is another leak downstream in the exhaust - water is leaking out behind the engine, and coming out the back of the boat around the stern drive (but not out with the exhaust thru the prop). No idea where that is coming from yet.
What else do I need to be checking for?

RT

If you're talking about water coming out of the lower sides of the transom while running, that's normal.

Replace the manifolds. Change the oil, run it and check it for water contamination. Don't panic and start tearing everything apart, go one step at a time and replace what is known to be bad, then diagnose from there.

 

[Mdavis]

Re: Cracked Exhaust Manifolds - what else to check?

I say you tell the wife that all your well knowledgeable colleges here on Iboats say its unrepairable. This way you can go get that new fancy pontoon you was drooling over last week.

All kidding aside.... if you have a cracked manifold I bet your block froze up sometime this year.

 

[180shabah]

Re: Cracked Exhaust Manifolds - what else to check?

well, if this might turn into a repower, DO NOT replace the manifolds yet. Presure test the cooling system. If the block is not cracked, then get new manifolds and continue.

Pics showing where the leaks are would be helpful, but lack of waterflow typically wreaks havoc on the bellows, tubes and shutters - all the non metal parts.

 

[rtflew]

Re: Cracked Exhaust Manifolds - what else to check?

Ran 2 tests tonight:

First, I pulled the plugs, grounded the coil wire and cranked it over. No sign of water coming out of the cyliners.

Then, w/ plugs out, I followed the updated Merc procedure I found linked on the forum to check compression - all cylinders were between 109 & 130.

Any chance this is a good sign regarding heads and/or block?

Thanks!

RT

 

[bruceb58]

Re: Cracked Exhaust Manifolds - what else to check?

The test you need to do is more complicated. You need to pressurize the cooling system. That means you have to block off the hoses going to the manifolds and the hose going up to the thermostat from the drive. You will need to rig up some pipe fittings into on of the hoses. Best thing to use is a tester for a gas line because it will have a schraeder valve and a gauge that you can fill the system with around 15 PSI of air.

 

[Bondo]

Re: Cracked Exhaust Manifolds - what else to check?

The test you need to do is more complicated. You need to pressurize the cooling system. That means you have to block off the hoses going to the manifolds and the hose going up to the thermostat from the drive. You will need to rig up some pipe fittings into on of the hoses. Best thing to use is a tester for a gas line because it will have a schraeder valve and a gauge that you can fill the system with around 15 PSI of air.

Ayuh,.... And then Listen,.... You'll Hear the Crack, follow the sound....

 

[rtflew]

Re: Cracked Exhaust Manifolds - what else to check?

Follow-up: Great News! Looks like the only issue was the cracked exhaust manifolds, the engine did great on the pressure-test! So working on replacing the manifolds now. Next up - work through the carb issues, and fixing the broken wire on the trim sender!

Thanks for everyone's input and advice - greatly appreciated!

RT

 

[zbnutcase]

Re: Cracked Exhaust Manifolds - what else to check?

Follow-up: Great News! Looks like the only issue was the cracked exhaust manifolds, the engine did great on the pressure-test! So working on replacing the manifolds now. Next up - work through the carb issues, and fixing the broken wire on the trim sender!

Thanks for everyone's input and advice - greatly appreciated!

RT

Cool! Always fun to dodge a bullet once in a while!

 

[svds]

Re: Cracked Exhaust Manifolds - what else to check?

Follow-up: Great News! Looks like the only issue was the cracked exhaust manifolds, the engine did great on the pressure-test! So working on replacing the manifolds now. Next up - work through the carb issues, and fixing the broken wire on the trim sender!

Thanks for everyone's input and advice - greatly appreciated!

RT

You might be a few bucks ahead if you can find a competent welder in your area.. I had both mine welded for $100. No leaks for 3 yrs

If your really frugal (like me) you can try JB Weld... didn't work perfect for me.. but might be worth a try. Good luck.

 

[HT32BSX115]

Re: Cracked Exhaust Manifolds - what else to check?

If your really frugal (like me) you can try JB Weld... didn't work perfect for me.. but might be worth a try. Good luck.

Um, don't do that!

Pat yourself on the back for being lucky!! Then buy yourself a set of manifolds (and risers, if you need them). One of the ways to ensure buying yourself a new engine is to try to use questionable manifolds and risers.....

 

[mcleaves]

Re: Cracked Exhaust Manifolds - what else to check?

Um, don't do that!

Pat yourself on the back for being lucky!! Then buy yourself a set of manifolds (and risers, if you need them). One of the ways to ensure buying yourself a new engine is to try to use questionable manifolds and risers.....

+10!

Just becasue you can see the crack on the outside does not mean that is the only compromised area. The wall between the exhaust and water jacket may be thousandths away from failure from an internal crack. The crack you see is just the place that gave out first. The rest of the cast is likely compromised in various areas. Heat it up with some exhaust and you'll have water in your cyls. I would not trust it.

 

[180shabah]

Re: Cracked Exhaust Manifolds - what else to check?

You might be a few bucks ahead if you can find a competent welder in your area.. I had both mine welded for $100. No leaks for 3 yrs...

Yours was the EXCEPTION, not the rule.

Most would waiste the $100 only to find that they were also cracked internally and still needed to be replaced.

Sorry, but a one in a million shot is not good odds when the loss is you engine, not just the mani's....