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

[kenny nunez]

A good time to look at the through hull intakes. Does your boat have one for each engine?

 

[mart284]

A good time to look at the through hull intakes. Does your boat have one for each engine?

Yes, one for each engine, extra one for genny on the bottom of the boat. We did check the flow while boat was in the water and there was water coming freely, but will physically check them anyway. Both filters were clean.

 

[Lou C]

Converting your readings from kPa to psi you have about 14 psi on the starboard engine and 20 on the port engine, not sure if that can cause a problem, did you get a trouble code for low water pressure? I know on my brother's boat he did and it limited the RPM due to the low water flow, he had only about 180*F on the gauge though. Your temps on both engines are pretty equal the read out is about 150-154, although the gauges read higher like 170...
You are also losing about 350 or so rpm on the starboard side.
Still the evidence doesn't add up. I'd think if you're cracking manifolds due to low water flow the starboard side engine would be running a good bit hotter.
Probably one of iboat's top ten inboard engine mysteries.

 

[mart284]

Converting your readings from kPa to psi you have about 14 psi on the starboard engine and 20 on the port engine, not sure if that can cause a problem, did you get a trouble code for low water pressure? I know on my brother's boat he did and it limited the RPM due to the low water flow, he had only about 180*F on the gauge though. Your temps on both engines are pretty equal the read out is about 150-154, although the gauges read higher like 170...
You are also losing about 350 or so rpm on the starboard side.
Still the evidence doesn't add up. I'd think if you're cracking manifolds due to low water flow the starboard side engine would be running a good bit hotter.
Probably one of iboat's top ten inboard engine mysteries.

Issue is, that NO ALARMS, NO BEEPS - nothing. Just cracks on the bloody manifold. Temps are fine, water and oil pressure is fine. Old gauges are not too reliable, they have been showing funny numbers all the time I owned the boat. One engine has been from the day one slower to speed up..
After quadruple checking everything, we still have no clue what is causing it. clear hoses show waterflow, heat gun did not show any differences'.

After seventh beer the great idea is that we have issue with water flow after having some longer 3800RPM stint and slowing down causes lack of water, exhaust is still hot and moment later cold water arrives. But why only one side, this probably requires more stronger drinks

Thanks for ideas and support - everything is appreciated (except - sell the boat)

 

[Lou C]

Well if you're on the seventh beer you're working on a 12 pack eh, I rate jobs by how many beers are required to prevent tools from being thrown, bad language used, in fact I had to switch to cussing in my mother's tongue (Italian) so the neighbors don't understand what I'm saying lol.
Getting back to the problem, cracking manifolds, if it isn't water flow, then I'm thinking it must be related to expansion when the engine heats up, I'm still wondering if the cyl head mating surface isn't even and when the manifold is torqued down but then heated, it is flexing unevenly and cracking.
Now I don't remember but have all the cracked ones been aftermarket, and not Mercruiser? If that's true I'd go at it again, use either a Merc or Barr manifold, measure the flatness of the mating surface, make sure that those bolts thread ALL the way in, for even clamping force, and keep your fingers crossed or as the Brits like to say "touch wood" lol!
It's a beautiful boat I'd hate to see you sell it.
I can tell you that when my engine overheated, the manifolds were at 375*F, and did NOT crack, OEM OMC one piece batwings, I tested them with acetone after that and used them 3 more seasons.

 

[mart284]

..
Getting back to the problem, cracking manifolds, if it isn't water flow, then I'm thinking it must be related to expansion when the engine heats up, I'm still wondering if the cyl head mating surface isn't even and when the manifold is torqued down but then heated, it is flexing unevenly and cracking.
Now I don't remember but have all the cracked ones been aftermarket, and not Mercruiser? If that's true I'd go at it again, use either a Merc or Barr manifold, measure the flatness of the mating surface, make sure that those bolts thread ALL the way in, for even clamping force, and keep your fingers crossed or as the Brits like to say "touch wood" lol!

All cracked manifolds are aftermarket ones and from two different brands - hard to get other in Estonia. We checked the surface and it was straight.

We will go first for water flow -pipe by pipe... and hope to find something there. If nothing at all, then for next cracked one in 2025 I will bite the bullet and order original one with customs and shippings and $$$$$. I hope it will not go that far, but I had similar hopes in last few times too

 

[cyclops222]

Has anybody cut open the manifolds to check if the CASTING is DEFECTIVE ? Compared to other cylinders where cooling water enters & exits ? Same area points to defective castings.
And or racing WOT for many minutes and then a sudden slow down. ........Cut open all the cracked pipe sections !! Also cut open none cracked sections. You have to see something different from the none cracked pipes.

 

[mart284]

Sad to state that nothing has been done with the boat - will start dismantling process next month... Sadly standing alone in the winterspot and waiting for a better summer...

 

[mart284]

Was too pissed to start the work last year and yesterday started the investigations again - there was a bit water in the manifold again
Will do now again the the test to find any cracks, blinds produced to close the holes and will pressurize the block and head to see if there are any leaks which we missed previously. Clearly the issue is with lack of water in the exhaust manifold while running with higher RPM-s.

... and the saga continues...

 

[mart284]

and no leaks!

Head and block does not leak air on 5 atm pressure test.

 

[alldodge]

I'm at a loss, and I would think about removing the single/three point drain and change to the seven point. Changing to seven point would get rid of the check balls and replace them with 90* elbows

https://www.mercruiserparts.com/bam/subassembly/31961/8093/210

 

[mart284]

I'm at a loss, and I would think about removing the single/three point drain and change to the seven point. Changing to seven point would get rid of the check balls and replace them with 90* elbows

https://www.mercruiserparts.com/bam/subassembly/31961/8093/210

Three point connector with ball was replaced to brand new one, no difference Ball is working nicely, you can close it by blowing inside.
We will go thru the pipes just to avoid that there is part of impeller or anything funny blocking the water on higher flow.

out of ideas. I did order brand new waterpump as I could not figure out what else to try..

EDIT: still 4 more months 'til I get back to water..

 

[cyclops222]

You certainly have the most unusual problem I have heard of in boating.
The very best to you.

 

[cyclops222]

To me it sounds like at WOT speed the water is reduced greatly there. It gets a super hot pocket. The motor slowing down finally causes the water to hit the casting spot causing a thermal shock crack.
But only a different manufacturer of the manifold would ever prove something like that.

 

[Scott06]

Three point connector with ball was replaced to brand new one, no difference Ball is working nicely, you can close it by blowing inside.
We will go thru the pipes just to avoid that there is part of impeller or anything funny blocking the water on higher flow.

out of ideas. I did order brand new waterpump as I could not figure out what else to try..

EDIT: still 4 more months 'til I get back to water..

Is there the possibility of reversion , not sure how this would cause cracks but just spitballing as this seems to have everyone stumped