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Mercury MPI 350 5.7L B3 Inboard

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WissGad340

New member
Hi All,

I have a Glastron GTS 225 with Mercury MPI 350 5.7L B3 Inboard, Yesterday during my boat trip had the Manifold completely exploded as per the pic, I could not share the video taken during this explosion. Did anyone experienced this with they engine ?
This engine is well maintained and flushing it all the time with Salt Away product.
If anyone had this on the same engine I will be very interested to know if they find out the cause of this.
Thanks

IMG_1471.jpgIMG_2393.jpeg
 
Ayuh,..... Are those cat. conv. manifolds,..??
If so,.... My guess is they needed replacin', Last year,....
 
So the outer casing cracked off ? was it not properly winterized and cracked? From the looks of it the inside exhaust wall is ok ? is that correct?
 
Dieter said:
So the outer casing cracked off ? was it not properly winterized and cracked? From the looks of it the inside exhaust wall is ok ? is that correct?
Click to expand...

Yes only the casing cracked, it was properly winterized but I am suspecting the flushing kit of mercury, I have the feeling The Salt away product don't go properly between the inner and outer casing.
What Kit are you using on yous Mercury MPI350 5.7L ?
 
The Salt away goes where the sea water goes... Possibly there is an internal blockage in the elbow that prevented proper flushing and also resulted in overheating and steam buildup.
 
WissGad340 said:
Yes only the casing cracked, it was properly winterized but I am suspecting the flushing kit of mercury, I have the feeling The Salt away product don't go properly between the inner and outer casing. What Kit are you using on yous Mercury MPI350 5.7L ?
Click to expand...
How old are they in salt water? typical life of 5-7 years. As others have mentioned probably blockage creating a hot spot which could crack it for sure.


I dont have an MPI - on the iboats forum I recall seeing a guy who removed his cats and then used a o2 simulator to fake out the ECU. I belive there are up and down stream o2 sensors before and after the cats. If the cat is not present you will get a fault code thinking the cat isnt working.
I think something like this https://www.magnumtuning.com/en/det...xygen-sensor-simulator/mercruiser/5-7-mpi-etc is used to bypass the cat.
If you replace these risers and manifolds with non cat I think you still need the upstream O2 sensoor so would need an o2 sensor plate like this https://www.hardin-marine.com/p-104396-o2-spacer-stock-mercury-riser.aspx
Havent seen these plates for dry joint manifolds so you would be back to wet joint (pre 2003) style center riser manifolds. IMHO the wet joint in salt water is more risk to the engine that the issues you are facing

Bottom line I'm sure you can find a way if you are handy to go back to the standard manifold and risers but there will be some issues to work through. Not sure if the juice is worth the squeeze...
 
sandkicker said:
The Salt away goes where the sea water goes... Possibly there is an internal blockage in the elbow that prevented proper flushing and also resulted in overheating and steam buildup.
Click to expand...


Looking more closely, it appears to me that part of the water passage is totally blocked. Its the part at the bottom of the pix ( which is the front of the elbow).... It's possible that this is core material from the casting process that was not properly removed. An EASY test is to take a small sharp object and scrape a small section ( about 1/2") long of the blocked passage to a depth of 1/2 to 3/4"" and inspect it. If it's core material, it will be very uniform and non magnetic. In this case, it's a MERC Q/C issue. It is also possible it is mud from a previous ( years ago??) encounter with a sand bar or mud bank.
 
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