bassfisher9615
New member
I’ve got a 200 mercury Efi 1998. I cold checked the compression when I test drove the boat and had 120 on all cylinders. Ended up buying the boat and on the 4th trip out I noticed it was peeing. We took it to a shop had the water pump and thermostats replaced. Hooked it back up and still no stream. Noticed that cylinder #3 was firing at 89 and all the others were at 120. Stuck a scope in there and it was very minor scoring, but could see where water vapor / steam was present. Also noticed on the head right beside that #3 spark plug there was white residue coming from the area that ran all the way down the head. Try to run my nail over the area but couldn’t really feel a crack of any sort. Just trying to get some other opinions before I say the motor is shot.