I have been fighting this cooling issue for a while now and now I have no other ideas. Engine is a 1990 Johnson GT200 (VJ200SLESE).
At idle, Port cylinders read close to 160, if not a little over. STBD side cylinders stay around 108-110. Compression is around 90psi on all 6, good spark, and water pressure is good. When the boat is up and running, port temp drops slowly to 120, but shoots right back up when I come off plane.
I have tried changing out port t-stat with a brand new one, swapping the STBD side t-stat to port, and finally ended up removing the port cylinder head. I found a small piece of plastic (from who knows what) stuck in the inside of the t-stat housing (pic). I thought that had to be the problem so I put on a new gasket and torqued it back down.
Still runs hot.
Could this be a carburetor issue, something more serious, or is this just the way its going to be?
And why is there so much more carbon build up on the bottom cylinder (pic)? Or, better yet, why are the top two so clean - water intrusion?
At idle, Port cylinders read close to 160, if not a little over. STBD side cylinders stay around 108-110. Compression is around 90psi on all 6, good spark, and water pressure is good. When the boat is up and running, port temp drops slowly to 120, but shoots right back up when I come off plane.
I have tried changing out port t-stat with a brand new one, swapping the STBD side t-stat to port, and finally ended up removing the port cylinder head. I found a small piece of plastic (from who knows what) stuck in the inside of the t-stat housing (pic). I thought that had to be the problem so I put on a new gasket and torqued it back down.
Still runs hot.
Could this be a carburetor issue, something more serious, or is this just the way its going to be?
And why is there so much more carbon build up on the bottom cylinder (pic)? Or, better yet, why are the top two so clean - water intrusion?
Last edited: