Hi
I have just finished replacing the manifolds and risers on my newly acquired boat which has a 305 small block 228hp Mercruiser. When I bought the boat, the engine had the original 'log style' manifolds with rear exit risers. I was advised to replace these due their age with newer style center exit manifolds, which I did. I also replaced the leg water pump, engine circulation pump and thermostat. I have retained the original style thermostat housing which has the six ports on it; two running to the risers and the other four to the front and rear of the manifolds.
Before starting all this work I ran the engine up on the flush muffs and the temperature gauge rose smoothly to normal operating temp, and stayed there. Now that I have finished replacing the parts the temperature gauge barely moves off the stop (it does, just), and the hoses are only tepid, not hot as I would expect. I took the boat out on the lake and although it runs sweetly the temperature just doesn't get to anywhere near normal operating range.
I have removed the new thermostat and tested it in a pot of water and it opens at 65 degrees celcius.
The manifolds I fitted are aftermarket, not OEM and they didn't come with installation instructions so I simply assumed that the hoses would go onto them in a similar fashion as they did on the old log manifolds, ie the hoses that used to go to the front of the manifolds were connected to the front, rear to rear, and riser hoses to risers.
The thermostat housing has the bypass around the thermostat which feeds directly into the risers, however the new gasket that came with it didn't have the cut out for this so I altered it to the pattern of the old one that I removed.
I should also mention that when I replaced the leg water pump that I discovered that it didn't have the extension tube or the rubber tube spacer on top of the pump housing ( "R" style leg), but rather there was an extra long rubber tube from the top of the leg which mated directly into the top of the pump housing.
Can anyone offer any suggestions as to why the engine is now running so cold, and what I could try to remedy it?
Could it be that the new pump(s) are providing much more circulation than the old ones, or should the rubber grommet be installed in the top of the pump housing to restrict the flow, or should I block off the thermostat bypass, or.........?
Please help!
I have just finished replacing the manifolds and risers on my newly acquired boat which has a 305 small block 228hp Mercruiser. When I bought the boat, the engine had the original 'log style' manifolds with rear exit risers. I was advised to replace these due their age with newer style center exit manifolds, which I did. I also replaced the leg water pump, engine circulation pump and thermostat. I have retained the original style thermostat housing which has the six ports on it; two running to the risers and the other four to the front and rear of the manifolds.
Before starting all this work I ran the engine up on the flush muffs and the temperature gauge rose smoothly to normal operating temp, and stayed there. Now that I have finished replacing the parts the temperature gauge barely moves off the stop (it does, just), and the hoses are only tepid, not hot as I would expect. I took the boat out on the lake and although it runs sweetly the temperature just doesn't get to anywhere near normal operating range.
I have removed the new thermostat and tested it in a pot of water and it opens at 65 degrees celcius.
The manifolds I fitted are aftermarket, not OEM and they didn't come with installation instructions so I simply assumed that the hoses would go onto them in a similar fashion as they did on the old log manifolds, ie the hoses that used to go to the front of the manifolds were connected to the front, rear to rear, and riser hoses to risers.
The thermostat housing has the bypass around the thermostat which feeds directly into the risers, however the new gasket that came with it didn't have the cut out for this so I altered it to the pattern of the old one that I removed.
I should also mention that when I replaced the leg water pump that I discovered that it didn't have the extension tube or the rubber tube spacer on top of the pump housing ( "R" style leg), but rather there was an extra long rubber tube from the top of the leg which mated directly into the top of the pump housing.
Can anyone offer any suggestions as to why the engine is now running so cold, and what I could try to remedy it?
Could it be that the new pump(s) are providing much more circulation than the old ones, or should the rubber grommet be installed in the top of the pump housing to restrict the flow, or should I block off the thermostat bypass, or.........?
Please help!
.
