2002 5,7 Mercruiser exhaust manifold keeps cracking - 5 times this summer

[Scott06]

What you have just makes no since as to why it's happening. If it was the manifold then why doesn't number 6 have same issue. The hoses are routed the same for both manifolds and in most all cases the port side does get a tad bit hotter the the starboard bank.

Scott's idea may provide some insight into the problem.
Take a short piece of clear hose and place in between the manifold connection and hose, and another piece between elbow and hose. Want to see if there are any bubbles in either hose

Yeah was thinking if there is air being sucked in either on inlet side of water pump (supply to engine) or if say a head gasket is putting combustion gasses into the cooling and it is allowing that manifold to get hot

 

[thedinz]

They forgot to install YOUR ORIGINAL exhaust risers.
Or put someone elses short risers on.
Only so many ways to crack Cast Iron Risers and Exhaust manifolds.
By now warped / leaking cylinder heads are a real possibility.
only other possibility
Is the engine oil on the dipstick a light brown color due to water in it ?
Rare possibility. Intake valves on 1 side sticking open ?
The water to reach the manifold from the back of the boat ?
Does anyone else drive the boat ?
Do you very quickly pull the throttle to idle when stopping ?
I feel they do not have a correct riser on that on side. If the riser is TOO short ? Water Hydro locking is REAL at normal driving. I helped remove sparkplugs from a hydrolocked engine 3 times on 1 cruise. Replacement engine did not have correct Risers.

Light brown oil? I always thought if there was water in the oil it would be milky?

 

[mart284]

Light brown oil? I always thought if there was water in the oil it would be milky?

Oil with water is milky stuff - confirmed.

 

[mart284]

Yeah was thinking if there is air being sucked in either on inlet side of water pump (supply to engine) or if say a head gasket is putting combustion gasses into the cooling and it is allowing that manifold to get hot

I can not see the outgoing side of the water as it exits thru elbow and back to the sea. I can only see if water is going to the spacer in my case and to the bottom of the manifold. And I am sure that waterflow is there - manifold outside temp on idle and on the run is similar to other 3 manifolds. I can also check them by removing one of the hoses and checking the waterflow with starter

 

[alldodge]

Connect clear hose to other end of hose prior to elbow

 

[Lou C]

I had blown HGs on my engine verified with the clear hose test but that didn’t crack the manifolds. Something is very odd about this problem I’ve been in this forum & others over 20 years & have seen a lot of problems but not this one! Whoever can solve this one deserves a prize!

 

[Scott06]

I had blown HGs on my engine verified with the clear hose test but that didn’t crack the manifolds. Something is very odd about this problem I’ve been in this forum & others over 20 years & have seen a lot of problems but not this one! Whoever can solve this one deserves a prize!

Absolutely can’t figure it either.

 

[mart284]

I had blown HGs on my engine verified with the clear hose test but that didn’t crack the manifolds. Something is very odd about this problem I’ve been in this forum & others over 20 years & have seen a lot of problems but not this one! Whoever can solve this one deserves a prize!

Sadly exactly the same issue was here in 2015, but the guy never wrote the solution

2003 Mercruiser 6.2 MPI Exhaust Manifold cracks

Hi Everybody, Hoping somebody can help us diagnose our exhaust manifold issues. When we first took out the boat, she ran great!! However, we did not turn the engine off at all on that trip. The second time we took the boat out, we sat on the water for a bit with the engine off and that is...

forums.iboats.com

 

[04fxdwgi25]

Personally, I would be leaning toward head / fuel delivery / head gasket, myself. Other 3 manifolds not doing it. This one has done it 3 times in close succession in the exact same spot. Just makes no sense. If water flow is good and correct risers are there and NOT leaking, then it needs to be mechanical ie: air / fuel delivery causing a lean / hot spot condition or possible crack / hole / bad gasket in water jacket.

Another possibility is wrong parts installed somewhere and being overlooked, due to assumption the correct part has been installed and has to be OK.

If / after the injectors check good, perhaps check wiring going to that injector and ensure it is good. Without going back thru this whole thread, did you swap ECM's and test?

After all this checks out then I would be looking at the head / gasket and possibly the intake (for a small vacuum lead on that cyl).

 

[Lpgc]

Do you know for sure the manifolds are cracked or do you assume they're cracked because water gets into engine cylinders?

I can't see how anything besides sudden heating / cooling (lack of or inconsistent cooling water flow), manifold torqued onto a cylinder head that has exhaust ports not flat (so bending and stressing the manifold), or defective manifolds could cause repeated manifold cracking.

If it has a closed cooling system and the manifolds are closed water cooled a head gasket issue could see bubbles and airlocks (exhaust gas locks) in manifold cooling water but this would still be 'lack of or inconsistent cooling flow'.

 

[mart284]

Personally, I would be leaning toward head / fuel delivery / head gasket, myself. Other 3 manifolds not doing it. This one has done it 3 times in close succession in the exact same spot. Just makes no sense. If water flow is good and correct risers are there and NOT leaking, then it needs to be mechanical ie: air / fuel delivery causing a lean / hot spot condition or possible crack / hole / bad gasket in water jacket.

Another possibility is wrong parts installed somewhere and being overlooked, due to assumption the correct part has been installed and has to be OK.

If / after the injectors check good, perhaps check wiring going to that injector and ensure it is good. Without going back thru this whole thread, did you swap ECM's and test?

After all this checks out then I would be looking at the head / gasket and possibly the intake (for a small vacuum lead on that cyl).

Do you know for sure the manifolds are cracked or do you assume they're cracked because water gets into engine cylinders?

I took one manifold for testing and it was confirmed that crack is thru the metal and water was escaping. Visible crack is always there. Can take the next one also to the test to verify once more - that job is not too costly

I can't see how anything besides sudden heating / cooling (lack of or inconsistent cooling water flow), manifold torqued onto a cylinder head that has exhaust ports not flat (so bending and stressing the manifold), or defective manifolds could cause repeated manifold cracking.

If it has a closed cooling system and the manifolds are closed water cooled a head gasket issue could see bubbles and airlocks (exhaust gas locks) in manifold cooling water but this would still be 'lack of or inconsistent cooling flow'.

I have sea water cooling, so no closed cooling part and head leak does not leave pressure in the cooling system

 

[mart284]

Personally, I would be leaning toward head / fuel delivery / head gasket, myself. Other 3 manifolds not doing it. This one has done it 3 times in close succession in the exact same spot. Just makes no sense. If water flow is good and correct risers are there and NOT leaking, then it needs to be mechanical ie: air / fuel delivery causing a lean / hot spot condition or possible crack / hole / bad gasket in water jacket.

Another possibility is wrong parts installed somewhere and being overlooked, due to assumption the correct part has been installed and has to be OK.

If / after the injectors check good, perhaps check wiring going to that injector and ensure it is good. Without going back thru this whole thread, did you swap ECM's and test?

ECM are not yet swapped
Water pump, map sensor, thermostat housing are swapped
Both head went to refurbishing after hydrolock and new good gaskets were installed afterwards

After all this checks out then I would be looking at the head / gasket and possibly the intake (for a small vacuum lead on that cyl).

 

[alldodge]

I took one manifold for testing and it was confirmed that crack is thru the metal and water was escaping. Visible crack is always there. Can take the next one also to the test to verify once more - that job is not too costly

We thought all were verified cracked in same place

Can test by using a piece of rubber and sandwich the elbow and manifold together, or use a piece of flat steel or even a 2x6 piece of wood. Then pressurize to 1 bar

 

[mart284]

We thought all were verified cracked in same place

Can test by using a piece of rubber and sandwich the elbow and manifold together, or use a piece of flat steel or even a 2x6 piece of wood. Then pressurize to 1 bar

Visual crack is always in the same location, will test the one currently in the boat. I do not have all the things on the marine to do this kind of testings.

 

[alldodge]

ok, if you can see the crack then don't bother with testing

 

[mart284]

...and all 8 injectors are good, will get the report also when I go and pick them up today. Now is fuel pressure check left and clear pipes to see how the water is flowing... Will change left and right side injectors just to have something swapped for elimination purpose.

 

[mart284]

 

[Lpgc]

View attachment 401021

Nothing wrong with the injectors then.
Tbh even if there were a problem with injectors or wiring I don't think it would lead to a cracked manifold. There should be enough water flow through the manifold to prevent hot spots from a lean mixture, if mixture was so lean might expect a burned exhaust valve before a cracked manifold anyway.

 

[mart284]

Nothing wrong with the injectors then.
Tbh even if there were a problem with injectors or wiring I don't think it would lead to a cracked manifold. There should be enough water flow through the manifold to prevent hot spots from a lean mixture, if mixture was so lean might expect a burned exhaust valve before a cracked manifold anyway.

next step is to measure fuel pressure and build see-thru hoses for waterflow verification, however manifold is not getting hot from outside...
A bit clueless with all that thing...

 

[Lpgc]

Plenty people are more experienced with boats and marine exhaust manifolds than me but I do know a lot about fuelling/mixture.

The amount of fuel an injector will flow for a given pulse length is related to the square root of fuel pressure minus manifold pressure, so the actual effect of none standard fuel pressure isn't always as much as might be assumed if we expected a direct link between fuel pressure and flow.

Maybe there's something I haven't thought of about how a lean mixture could lead to a cracked manifold but fuelling/mixture seems an unlikely cause to me, especially if the engine seems to have normalish power.

I'm more interested in the results of the see-thru hoses test than fuel pressure test. It will show you if there are any bubbles but won't tell you how much flow is going through it.

I'd need to re-read the thread to remind myself if your boat has one or two engines. If the see-thru hose test didn't reveal anything and if it had two engines I'd be taking the manifold off the other engine to put on the engine that cracks manifolds and putting a new manifold on the other engine, see if a new one cracks on the good engine. Seems more like inconsistent water flow to me though, but like I say others have more experience with boats.

Definitely sure it doesn't get hot in the area where it cracks, maybe when you're driving the boat and can't keep a hand on it to monitor the temperature? Even if it got very hot when driving, if you had to come from the helm to put a hand on the engine after driving it could be enough time for water to enter the manifold and cool it before you do the hand temperature test.