Hi folks,
I have developed a low compression problem on #4 and #6 cylinders in my 1996 250hp Mercruiser 5.7LX EFI Bravo III. The boat is indoor rack stored and has about 650 original hours. It is raw water cooled but it spent most of its life in fresh water until I bought it and moved it to CT 5 years ago.
Tuesday night I went out to do a little fishing and noticed a ticking sound while cruising at 3,000 rpm. I backed off to idle and the engine sounded normal and smooth. I headed back to the marina but when I brought the revs up to 2,500 it began to make noise again. There was also a noticeable roughness and loss of power. I idled in without incident and submitted a service request with my marina to diagnosis the problem. The engine did not overheat and oil pressure was normal. There is no sign of water in the oil.
On Friday I learned the service department has a major backlog and they didn?t know if they could even look at it for the ?next several? weeks?..Yikes! I decided to look into it myself this weekend. I discovered that I had three loose spark plugs on the starboard side. #2 was not snug but #4 and #6 were much more loose and no question leaking compression out around the plug. Problem solved I thought. I tightened all the plugs and did a sea trial but still had the same symptoms. I removed all the plugs and did a compression check with the following results?.
#1-140, #3-145, #5-145, #7-145, #2-145, #4-40, #6-40, #8-150.
My first thought is a bad head gasket but I am interested in hearing your thoughts.
My plan is to have the boat put on a ground stand and I will pull the heads with the motor still in the boat (there is enough room to work around the engine thankfully). If I find a bad head gasket should I still take the heads to an engine shop and have them checked over? What else I should do while I?m in there besides gaskets? I have a fair amount of mechanical experience but appreciate any tips you might have.
Thanks,
HNT
I have developed a low compression problem on #4 and #6 cylinders in my 1996 250hp Mercruiser 5.7LX EFI Bravo III. The boat is indoor rack stored and has about 650 original hours. It is raw water cooled but it spent most of its life in fresh water until I bought it and moved it to CT 5 years ago.
Tuesday night I went out to do a little fishing and noticed a ticking sound while cruising at 3,000 rpm. I backed off to idle and the engine sounded normal and smooth. I headed back to the marina but when I brought the revs up to 2,500 it began to make noise again. There was also a noticeable roughness and loss of power. I idled in without incident and submitted a service request with my marina to diagnosis the problem. The engine did not overheat and oil pressure was normal. There is no sign of water in the oil.
On Friday I learned the service department has a major backlog and they didn?t know if they could even look at it for the ?next several? weeks?..Yikes! I decided to look into it myself this weekend. I discovered that I had three loose spark plugs on the starboard side. #2 was not snug but #4 and #6 were much more loose and no question leaking compression out around the plug. Problem solved I thought. I tightened all the plugs and did a sea trial but still had the same symptoms. I removed all the plugs and did a compression check with the following results?.
#1-140, #3-145, #5-145, #7-145, #2-145, #4-40, #6-40, #8-150.
My first thought is a bad head gasket but I am interested in hearing your thoughts.
My plan is to have the boat put on a ground stand and I will pull the heads with the motor still in the boat (there is enough room to work around the engine thankfully). If I find a bad head gasket should I still take the heads to an engine shop and have them checked over? What else I should do while I?m in there besides gaskets? I have a fair amount of mechanical experience but appreciate any tips you might have.
Thanks,
HNT
