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

[alldodge]

Restrictor should be next to exhaust elbow
Gasket

 

[mart284]

Restrictor should be next to exhaust elbow
Gasket

Thank you! I am still confused as there are this statement:

Purpose of the Restrictor Hole Design​

The purpose of the restrictor hole is to prevent the cold bypass water as it enters the exhaust elbow, from back-flowing down and into the manifolds. If the restrictor hole is positioned incorrectly the cold bypass water will flow downward into the manifold and prevent the manifold temperatures from heating up enough to prevent condensation.

And my water inlet is in the spacer so this means I should have the restrictive gasket below water inlet and based on the picture as bottom one?

 

[alldodge]

Your correct, restrictor goes next to manifold

I'm looking at the manual prior to posting link and looked like PPT posted it correctly, so I linked it for visual.

Comparing PPT to manual I see PPT is showing how to place gasket with a closed cooling, BUT they should be showing a block off gasket

 

[mart284]

Your correct, restrictor goes next to manifold

I'm looking at the manual prior to posting link and looked like PPT posted it correctly, so I linked it for visual.

Comparing PPT to manual I see PPT is showing how to place gasket with a closed cooling, BUT they should be showing a block off gasket

Ok, so we had this one also in the correct place - now only thing to check is that water is flowing on all the pipes. Also ordered new thingy with small ball inside below the manifold where 2 pipes are connected - it seems that ball inside the connector was not moving freely.
I am still out of ideas

 

[alldodge]

The thingy is a check ball and is used to restrict water from coming in past it when running. It allows water to pass in other direction during winterization

 

[mart284]

Thanks!
New manifold will reach me this week and before dismantling will check water flow on all the piping. If there is water freely flowing, what next?

I assume I should find a bad hose somewhere...

 

[alldodge]

I'm thinking something is restricting water flow to that manifold somewhere. Compare this motor to the other one

 

[Bt Doctur]

 

[Scott06]

I'm thinking something is restricting water flow to that manifold somewhere. Compare this motor to the other one

Agreed that is the only thing that makes sense that there is no water flow through the manifold either via the supply to bottom of manifold or supply to riser is keeping water from entering the manifold.

 

[mart284]

Both engines are having pipes in the exact same manner. Restrictive seal is under the water hose. As I am still waiting for manifold to arrive to Estonia, I did not do the hose checks. Also new thingy where 2 water lines are connected below manifold is ordered, if that ball there got stuck on the wrong mode and blocked the water, it will be replaced as well.

I do hope I can find the blocked water hose somewhere...

 

[mart284]

Update and what was done:
- new manifold obviously with new thingy with ball inside for 2 pipes to connect in the bottom of the manifold, also checked the surfaces, no bends or irregularities
- checked water flow, cleaned filter (did not find any debris inside)
- checked all the water pipes and heat exchanger - no issues found,
- changed water pumps between engines and added new impeller
- changed thermostat housing between engines and added 70c thermostat on both sides
- changed MAP sensors between engines
- first idle run was with thermal camera and checked the temps on both engines, on all the pipes going there, water coming out from the side exhaust - all the same
- first sea trial was day before yesterday and did check everything again after 15m fast drive, temps all fine and both engines running in similar numbers. Camera did not show any differences between engines nor side of the engines

ONLY difference is fuel consumption - problematic engine is showing much higher fuel per hour on same engine speeds

After two short trip I have again water in the engine... and out of ideas. I can see that water is on the same cylinder and all the cracks are in the same place...

HELP with ideas, please??

Screenshot from fuel difference
Sparkplugs

 

[mart284]

on the positive note - manifold change is doable now within 1,5 hours

 

[04fxdwgi25]

Are you 100% sure the manifolds are actually cracking?

 

[mart284]

Are you 100% sure the manifolds are actually cracking?

YES, visible crack and went to the shop to test it with pressure, bubbles were coming thru from the crack in watertank

 

[mart284]

And all 5 cracks are on 5th cylinder

 

[mart284]

One idea from the field - can this be linked to faulty injector on that cylinder? Low on fuel and burning too hot causing manifold to crack?? I will measure fuel pressure and take the injectors for checkup next week.

 

[alldodge]

One idea from the field - can this be linked to faulty injector on that cylinder? Low on fuel and burning too hot causing manifold to crack?? I will measure fuel pressure and take the injectors for checkup next week.

Possible and about the only thing left
Would be good to have injectors flow tested

 

[alldodge]

Possible and about the only thing left
Would be good to have injectors flow tested

Another thought is if the cylinder is running lean and causing enough heat to crack the manifold then it should also warp the valves, and that's not happening

 

[Scott Danforth]

Check compression on the suspect engine. Especially on cylinder 5

 

[cyclops222]

I looked at that cooling diagram that was posted. UUUGGHH

Why does it have so much CRAP ?? Same engine ina car does not. Older boat engines HAD a simple Circuiting Pump, thermostat and a sometimes installed flow diverting metal plate in the exhaust outlet of the engine Circulating Pump. DONE
That engine is built to have problems.
How do you find bits of raw water rubber impellor blade tips ? Or any other parts ?
WE completely removed the balancing valve in my 2002 5.0L Ran with a O K constant slight difference between both sides of the engine.
The water MUST flow instantly And almost equally to all parts of the engine to prevent the overheating of 1 side.