BigWill1985
New Member
- Feb 6, 2010
- 17
- Boat Info
- 1992 Celebrity 200 Cuddy Cabin
- Engines
- 260hp Chevrolet 350 with a Mercruiser outdrive
I know that my boat isn't a Searay, but I joined this forum before buying this boat and I know you guys know what you're talking about.
OK. So the boat in my signature is giving me some problems. Here are the specs:
Chevrolet 350 crate motor (replaced 1.5 years ago)
Freshwater cooling system
Replaced lower unit impeller about half-way through last season, with not much use since
Thermostat removed with orifice plate installed in it's place (has always maintained ~160+/-20*F at all times)
Entire system cleaned out and flushed after each run
Mercruiser Alpha 1 lower unit
I have ran it 3-4 times this year, without any issues at all. It has sat at my dock for the last few weeks (in the water), and we got ready to take it out this past weekend. Made it about 100 yards away from the dock, and the engine started overheating (boiling the water out of the top of the heat exchanger).
So, I started troubleshooting. Refilled the coolant system, and started it up. Fired right off. Did a compression test, with all cylinders around 130psig with the exception of #4 which had 95psig. I honestly think that the issue with the cylinder having lower compression is due to needing the valves adjusted (had the head off of the even bank towards the end of the season last year). The motor still fires up and runs great (firing on all cylinders). At idle and up to plane, the boat maintains temperature at about 170*F. Anything over about 3000RPM, and the temperature will slowly rise until I back off when it will come back down within ~2 minutes. I pulled off the brackish water dumps at the exhaust manifolds, and had plenty of flow from each hose. I hooked up each individual dump to each manifold, and had very little back pressure on the open ended hose from each side. Pulled the boat out of the water, hooked up the ear muffs, and the motor runs great with solid flow out of the lower unit (from both manifolds).
I am lost. It looks like I have good freshwater flow from each side. I have the most flow through the system I can possibly have (without the issue of having a thermostat sticking). I have good compression which tells me I shouldn't have a bad head gasket or cracked head.
Any thoughts on what direction I should head? I am planning on breaking open the heat exchanger tomorrow to ensure it has no fouling of the tubes. I don't think the impeller needs to be replaced, since I have pretty good flow through the system. Do you think there may be an issue with exhaust back pressure restricting flow of the brackish water side at high RPM's (maybe the exhaust valve is not adjusted properly)? I'm just taking shots in the dark... This thing has me beat right now....
All help will be greatly appreciated. I am pretty mechanically inclined, and have worked on many other vehicles (and have had this boat torn down from top to bottom several times).
Thanks again, guys!
~Will Courtier~
OK. So the boat in my signature is giving me some problems. Here are the specs:
Chevrolet 350 crate motor (replaced 1.5 years ago)
Freshwater cooling system
Replaced lower unit impeller about half-way through last season, with not much use since
Thermostat removed with orifice plate installed in it's place (has always maintained ~160+/-20*F at all times)
Entire system cleaned out and flushed after each run
Mercruiser Alpha 1 lower unit
I have ran it 3-4 times this year, without any issues at all. It has sat at my dock for the last few weeks (in the water), and we got ready to take it out this past weekend. Made it about 100 yards away from the dock, and the engine started overheating (boiling the water out of the top of the heat exchanger).
So, I started troubleshooting. Refilled the coolant system, and started it up. Fired right off. Did a compression test, with all cylinders around 130psig with the exception of #4 which had 95psig. I honestly think that the issue with the cylinder having lower compression is due to needing the valves adjusted (had the head off of the even bank towards the end of the season last year). The motor still fires up and runs great (firing on all cylinders). At idle and up to plane, the boat maintains temperature at about 170*F. Anything over about 3000RPM, and the temperature will slowly rise until I back off when it will come back down within ~2 minutes. I pulled off the brackish water dumps at the exhaust manifolds, and had plenty of flow from each hose. I hooked up each individual dump to each manifold, and had very little back pressure on the open ended hose from each side. Pulled the boat out of the water, hooked up the ear muffs, and the motor runs great with solid flow out of the lower unit (from both manifolds).
I am lost. It looks like I have good freshwater flow from each side. I have the most flow through the system I can possibly have (without the issue of having a thermostat sticking). I have good compression which tells me I shouldn't have a bad head gasket or cracked head.
Any thoughts on what direction I should head? I am planning on breaking open the heat exchanger tomorrow to ensure it has no fouling of the tubes. I don't think the impeller needs to be replaced, since I have pretty good flow through the system. Do you think there may be an issue with exhaust back pressure restricting flow of the brackish water side at high RPM's (maybe the exhaust valve is not adjusted properly)? I'm just taking shots in the dark... This thing has me beat right now....
All help will be greatly appreciated. I am pretty mechanically inclined, and have worked on many other vehicles (and have had this boat torn down from top to bottom several times).
Thanks again, guys!
~Will Courtier~
