tginz
New Member
I have been tracking this issue for sometime. The starboard side rear plug always seems to be oily when I remove it. Let me back up...I have a 2004 5.0 MPI manufactured in 2003 with freshwater cooling & a 160 t-stat. The motor currently has 174 hours and runs beautifully. Last spring I pulled the plugs for the first time, which was splitting Mercruiser's 300 hrs. Service interval in half. The rear starboard plug was oily and appeared oil burnt. There was an oily goo literally leaking from the spark plug threads. The next one forward on the starboard side showed similar signs but was much better and the remainder port & starboard were in good condition.
I changed all of the plugs and did a compression test on all 8 cylinders. Each gave me between 184-192 psi. The higher numbers were on the two rear starboard (oily) cylinders. When I picked up the plugs at my Mercruiser dealer, I showed them the fouled plug. The mechanic was not surprised and didn't see it as a problem, he said they are seeing lots of this with the new fuel issues. He had no explanation and only suggested - Maybe that cylinder runs really cool. I suggested doing a leak down test and he seemed to think - good compression is good compression. Mercuiser minimum spec. for compression for an 03' 5.0 MPI is 100psi., that seemed low, but I verified it in my Seloc manual. Yet still don't believe either one.
I've run 32 hours this season and just pulled the plugs again. All plugs were excellent, like new, yet this one rear starboard had oil on the threads and signs of oil burns. I again tested compression and came up with 189, no change.
Based on the plug condition, I would assume a oil burning issue, BUT in 30 hours of which 20 was 3,300 rpm running, I haven't lost any oil. The dipstick still reads on the full mark and relatively clean.
Any suggestions as to what would cause an oily appearance to a spark plug and threads in a solid compression tested cylinder? Can oil weep from somewhere else when it sits for long periods? I simpy can't figure this one out.
Given the excellent compression numbers and no oil loss and surely NOT going to tear into this motor, but I would like to know why I'm getting this condition in one cylinder...............
Thanks for any suggestions...my brain is getting tired.....:smt021
I changed all of the plugs and did a compression test on all 8 cylinders. Each gave me between 184-192 psi. The higher numbers were on the two rear starboard (oily) cylinders. When I picked up the plugs at my Mercruiser dealer, I showed them the fouled plug. The mechanic was not surprised and didn't see it as a problem, he said they are seeing lots of this with the new fuel issues. He had no explanation and only suggested - Maybe that cylinder runs really cool. I suggested doing a leak down test and he seemed to think - good compression is good compression. Mercuiser minimum spec. for compression for an 03' 5.0 MPI is 100psi., that seemed low, but I verified it in my Seloc manual. Yet still don't believe either one.
I've run 32 hours this season and just pulled the plugs again. All plugs were excellent, like new, yet this one rear starboard had oil on the threads and signs of oil burns. I again tested compression and came up with 189, no change.
Based on the plug condition, I would assume a oil burning issue, BUT in 30 hours of which 20 was 3,300 rpm running, I haven't lost any oil. The dipstick still reads on the full mark and relatively clean.
Any suggestions as to what would cause an oily appearance to a spark plug and threads in a solid compression tested cylinder? Can oil weep from somewhere else when it sits for long periods? I simpy can't figure this one out.
Given the excellent compression numbers and no oil loss and surely NOT going to tear into this motor, but I would like to know why I'm getting this condition in one cylinder...............
Thanks for any suggestions...my brain is getting tired.....:smt021