I have big problems with my 1980 SeaRay with 260 GM Mercruiser. It has the log style manifolds with the rear risers.
Here's the story.
I replaced the manifolds about 4-5 years ago but not the risers. My guess is the risers are 7-8 yrs old.
The operating temperature started creaping up over the last year, so I figured things were starting to clog up. It's a raw water only system in salt water.
I took the boat for a ride this past weekend and the temperature went up to about the red line within 10 minutes, so I turned around and headed back to the dock. It was just on the red line and no higher. I shut it off and waited for it to cool. While off I checked the oil and it was clean. When I tried to start it, it wouldn't budge. I thought it was connections, or the battery needed a charge so I put a charger on and left it on overnight. The next day it turned over but with a clunk on every revolution. It cranked a long time to start and finally started, but didn't run right and only at about 1500 RPM's. After about 10-20 seconds it started rev'ing higher and seemed okay so i shut it down and didn't let it heat up.
My plan was to replace the risers, so I started taking them off. I pulled the dip stick to get at a bolt and I saw the dreaded sight of milk on the stick.
I'm hoping it's not a head problem or block problem. What I think happened, is that water backed up into the cylinders from the exhaust manifold and overnight seeped down into the pan.
What I find odd is that the 78-82 Mercruiser GM V8 uses a SS blocking plate between the manifold and riser. There is a hose on each end of the manifold and one into the riser. all 3 hoses come from the thermostat housing block. How does the water circulate through the manifold?? Is the hose on the back end of the manifold a return line? It looks to me that they would all be outputs from the thermostat housing block? The three passage ways on the risers were completely blocked, but with the SS blocking plate, it seems they don't do anything anyway. There is just a small hole about 1/8 inch in the SS blocking plate to pass water. I took the risers off in the water and the water level is about 4 inches down into the rubber boot that connects to the exhaust pipes. The level bounces up and down as the outside water bounces up and down. Is there supposed to be a flap in the exhast manifold preventing water backup?
Any ideas on what may be happening would be appreciated.
Thanks,
Sorry for the long post, but i wanted to give as much info as possible
Here's the story.
I replaced the manifolds about 4-5 years ago but not the risers. My guess is the risers are 7-8 yrs old.
The operating temperature started creaping up over the last year, so I figured things were starting to clog up. It's a raw water only system in salt water.
I took the boat for a ride this past weekend and the temperature went up to about the red line within 10 minutes, so I turned around and headed back to the dock. It was just on the red line and no higher. I shut it off and waited for it to cool. While off I checked the oil and it was clean. When I tried to start it, it wouldn't budge. I thought it was connections, or the battery needed a charge so I put a charger on and left it on overnight. The next day it turned over but with a clunk on every revolution. It cranked a long time to start and finally started, but didn't run right and only at about 1500 RPM's. After about 10-20 seconds it started rev'ing higher and seemed okay so i shut it down and didn't let it heat up.
My plan was to replace the risers, so I started taking them off. I pulled the dip stick to get at a bolt and I saw the dreaded sight of milk on the stick.
I'm hoping it's not a head problem or block problem. What I think happened, is that water backed up into the cylinders from the exhaust manifold and overnight seeped down into the pan.
What I find odd is that the 78-82 Mercruiser GM V8 uses a SS blocking plate between the manifold and riser. There is a hose on each end of the manifold and one into the riser. all 3 hoses come from the thermostat housing block. How does the water circulate through the manifold?? Is the hose on the back end of the manifold a return line? It looks to me that they would all be outputs from the thermostat housing block? The three passage ways on the risers were completely blocked, but with the SS blocking plate, it seems they don't do anything anyway. There is just a small hole about 1/8 inch in the SS blocking plate to pass water. I took the risers off in the water and the water level is about 4 inches down into the rubber boot that connects to the exhaust pipes. The level bounces up and down as the outside water bounces up and down. Is there supposed to be a flap in the exhast manifold preventing water backup?
Any ideas on what may be happening would be appreciated.
Thanks,
Sorry for the long post, but i wanted to give as much info as possible