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

[Lou C]

Most mechanics I know around here like BARR if you aren't using OEM.
I have to say this is one of the most mysterious engine problems I have come across.
While some might argue, I think BARR is very close to OEM quality. Other than the cyl head on that side being out of level as far as the exhaust ports, or a clogged water passage that puts much more heat in one spot, it is very hard to imagine what's causing this.
When I had my bad overheat (raw water hose from transom popped off P/S cooler on back of the engine) the manifolds got to 375*F (temp spiked but bilge was very quickly filling with water....I was trying to beach the boat, didn't know why at that point water was filling the bilge, lol), and they were the infamous batwings and THEY didn't crack! Used them 3 more seasons! Waiting for the tow in, I took out my IR temp gun and measured them for a good laugh on a bad day.
However I found out a few years later, the cyl heads did crack, yet, till the HGs started leaking, it ran the same as always.

 

[alldodge]

I just cannot believe it's the manifold

 

[Scott Danforth]

Barr is one of the OEM casting houses

 

[mart284]

I live in Europe and I can buy RecMar or Sierra parts here, probably can order OEM as well, but with long delivery and proper taxation... I do not think it is issue with bad quality manifold. It has to be something, what triggers it ( being an engineer, it is simple - either too much heat and sea water after that or too much heat and cold water after that).
Also checking on timing, if the timing is off, burn will be later and causing extra heat on exhaust side. Why did we not see that part with IR gun, is still a mystery for me...


Water flow with see thru pipes were tested, IR gun used. Now we plan to measure fuel pressures and once again mercury diagnostic tool for checking all the sensors. Motor is running with a bit different sound than the good one, hence we should have the issue with something. Also noticed that cold start on both engines are good, but good engine will have a bit higher RPM on idle (730) and when warm, will go down to 630-650. Bad one will start at 630 and stays there.

Anyway - no sea trials before we found something not working as it should...

 

[cyclops222]

Never said this before. Possible bad casting molds or process.

 

[Lpgc]

I live in Europe and I can buy RecMar or Sierra parts here, probably can order OEM as well, but with long delivery and proper taxation...

I'm in England, recently changed the manifolds on my Volvo/OMC Cobra/Ford302 engine. At the time I bought them the marina only had the slightly more expensive Barr manifolds in stock but the marina said they were a better quality / premium brand, I decided I'd buy the Barr brand anyway.

 

[cyclops222]

Barr was excellent more than 50 years ago. How has your new Barr manifold done? For how many trips ?

 

[cyclops222]

A slightly, occasionally, sticking open valve can cause that slightly different engine sound. We are being forced to check out really RARE causes.
I forget. Does that sparkplug look bad after the crack forms ?

 

[Scott06]

I live in Europe and I can buy RecMar or Sierra parts here, probably can order OEM as well, but with long delivery and proper taxation... I do not think it is issue with bad quality manifold. It has to be something, what triggers it ( being an engineer, it is simple - either too much heat and sea water after that or too much heat and cold water after that).
Also checking on timing, if the timing is off, burn will be later and causing extra heat on exhaust side. Why did we not see that part with IR gun, is still a mystery for me...


Water flow with see thru pipes were tested, IR gun used. Now we plan to measure fuel pressures and once again mercury diagnostic tool for checking all the sensors. Motor is running with a bit different sound than the good one, hence we should have the issue with something. Also noticed that cold start on both engines are good, but good engine will have a bit higher RPM on idle (730) and when warm, will go down to 630-650. Bad one will start at 630 and stays there.

Anyway - no sea trials before we found something not working as it should...

Would definitely rule out the timing but usually if it is late the engine will run hot

 

[Lpgc]

Barr was excellent more than 50 years ago. How has your new Barr manifold done? For how many trips ?

If you're asking me, mine have been great but only fitted earlier this year and done less than 200 hours all on fresh water.

 

[Lou C]

I installed my Barr exhaust some time back they now have 5 seasons in salt water. Will prob replace end of next season which is normal in salt water….no problems fit well and no leaks…

 

[mart284]

So engine is running and still no cracks, also no culprit found. Plugs are OK (one is not iridium as one was broken and repaced with normal one). Fuel pressure on both engines is same.
Two error codes are visible on both engines, no issues seen with sensors or nothing bad sticks out.

What we noticed - if both engines are running ca 3700 RPM-s good one had 60% throttle open and bad one 83%. Also starting with full throttle good engine is getting higher rpms faster, bad one is equal up to 2500 and then seems to lose power...

Will swap fuel pumps and check timing under load. Manifold is not hot, but I can see steam on exhaust.. Still puzzled on the reason, why I have this crap here

Fuel pressure test

 

[alldodge]

Plugs don't look bad, but different types is not good


Codes


I'm not finding the fault code

Think I'm seeing less then 40 psi on gauge?

 

[mart284]

Fuel pressure was 34 on both engines. We did not test it under the load, but probably do that as well, engine is less powerful over 2500 RPM, throttle is open way more to have the same speed on both engines.

Today's plan is to swap fuel pumps between the engines.

PS - those fault codes are same on both engines - code 075 Fuel level circuit active.
Second alarm was about steering.

 

[mart284]

End of the shittiest season finally arrived - last few days went for testing under load and all seatrials did not show any differences between engines. I have a feeling that despite the fact that everything was changed between the engines, issue still relies with water flow. Noticed that there was a lot more air after 3800 rpm drive on the faulty side pipes AND water pressure is lower on that side as well. As sensor was swapped and pumps as well without any major change, there has to be some blockage somewhere.
That will be the winter project now.
Here is the run with WOT
Bubbles in the hoses
and liftoff...

 

[Lou C]

Given that the water pressure is lower on the starboard side & more bubbles in the feed hose it seems that air is getting sucked in somewhere in the raw water circuit…

 

[alldodge]

Little extra bubbles but I'm not seeing enough to make the manifold crack

 

[Scott06]

End of the shittiest season finally arrived - last few days went for testing under load and all seatrials did not show any differences between engines. I have a feeling that despite the fact that everything was changed between the engines, issue still relies with water flow. Noticed that there was a lot more air after 3800 rpm drive on the faulty side pipes AND water pressure is lower on that side as well. As sensor was swapped and pumps as well without any major change, there has to be some blockage somewhere.
That will be the winter project now.
Here is the run with WOT
Bubbles in the hoses
and liftoff...


View attachment 402488

I think one of the guys here Ted was chasing a water flow issue between twin engines that ended up being zebra mussels growing inside passages in the drive or bellhousing.

What ever it is a Lou said this is one of the more perplexing issues seen on this forum. You are not missing anything stupidly obvious or simple.

 

[Lou C]

With boats in salt or brackish water it’s common to have to clean out the water intakes if the boat is docked or moored in the water. I had to split the upper & lower gear housings to totally clean out the water intake area on mine. But even though the growth caused warm running (175-185) never cracked a manifold. Just watching the vid the most glaring difference is the water pressure readings. I think air is getting in but again not sure if that would crack a manifold…
My brother had a 2020 Chap with the Merc 4.5 Alpha that he kept in the water by the 3rd season it was starting to overheat & he asked me what to check and I told him to tilt the drive all the way up & rod out the water intakes. That fixed it but he traded it on a similar boat with an outboard.

 

[mart284]

Will start the "pipe dismantling" project in November to see, if there are something inside the pipes or water chanelles, also will check that water inlet is clean - filter was and water is flowing, but something somewhere most block the flow. Anyway - IF I will reach to some conclusion, will let you know here as well.