Logo

Bad cylinder head history

another

New member
"5.7 Merc MPI's. Starboard

"5.7 Merc MPI's. Starboard engine has port cylinder heads replaced twice, starboard side head once. Now starboard side needs replacement. Both sides done under new boat warranty, second time with @300 hours. Seems like a lot of cylinder head replacements for a six year old boat. Mercruiser doesn't seem too interested. Anybody got any helpful advice on what seems like an on-going problem? I thought these were pretty reliable engines. Anybody?"
 
"Why do they have to relace th

"Why do they have to relace the heads? are the intake valves going bad?(tulip-ed)?
It has been awhile, but we had one boat that kept going through intake valves,one time in 12 hrs run time.
found the boat was over propped.
just a thought."
 
"allan,

thanks for the repl


"allan,

thanks for the reply.Low compression readings led to diagnosis. I'm not a mechanic but assume valves causing problems."
 
"sounds like the "root cau

"sounds like the "root cause" of the problem has not been fixed. Whatever killed the first head, continues to kill all subsequent heads because it has not been fixed. Running lean for example can cause valves to overheat and fail. Needs to get a complete diagnosis by a tech that can troubleshoot. We can start asking all the questions here, but a competent tech is going to have to enter the picture some point- if you aren't wrenching, your mechanic is going to love having you give him tips from an internet message board....

First Question they should ask you: What WOT rpm does your boat run at? The wrong prop can do it."
 
I second the prop thing but wo

I second the prop thing but would deffinately check into the fuel mixture sounds like a leaning out problem
 
"You guys are great for postin

"You guys are great for posting up on this problem. Good point Hy Stat about trying to fix it over the internet. I'm not turning the wrenches and the latest tech is an authorized Merc shop. I contacted Mercruiser to see if they would get involved because of the history, they said start with local authorized service. Local service responded with a $450 compression check to confirm the local yard, and said for $1050 they would take the head off to find out if it is a bad valve or something worse (burned piston?). I'm trying to say to Mercruiser AND local authorized service I'm more concerned about what's causing the motor to break than I am what's broke....I can't seem to get them to understand that there is a history of failure...like you guys have caught on to immediately....go figure....thanks again for the input....anybody know a mechanic in North Carolina..??.."
 
"One thing that might give som

"One thing that might give some indication is to have the tech pull any stored codes. There may be a history of knock sensors detecting knocking, which would sure be an indication of mixture too lean and/or lugging caused by over-propping.

There may be something else causing the port engine to run lean such as a bad TPS, MAPT sensor, low fuel rail pressure, etc. It does seem likely that you will continue to have head/valve problems until the root cause is found.

Rod"
 
"Hy Stat, I'm embarrased t

"Hy Stat, I'm embarrased to say I don't know what WOT rpm's are for this boat. It cruises 25mph@3000, which is about what the Regal spec is. If cruise speed/rpm's line up would that tell you if it's propped right?"
 
Back
Top