Ok guys i will try to explain from the beginning. Lost the 5.0 last Sept 30 mile off of Fort Bragg tuna fishing. manifolds decided to rust through. Always fan very well for a 2000 hour saltwater engine
In April we bought a new bobtail 350 mag mpi..I installed it myself, ,also went with a full closed water cooling system. everything went smooth. first shake down run took the boat to a local reservoir. (Oh ya the boat, its the 2001 Bayliner trophy 23' lives on a trailer very clean boat ) So engine seemed to run real good for first 15 min wile checking for leeks ect.. i asked it to get up on plain. Plenty of power Jumped up out of the hole couldn't of slapped the smile off of my face. temps climbed quick with in 2 min alarm was singing, So i backed it down to a idle and temp came down quickly to about 175deg (dash gauges) i forgot the one tool that i really needed the temp gun. I did that about 5 times not letting it get to 190-195 before i would let it cool, hoping maybe a air bubble needed to be worked out. Very discouraged i put it back on the trailer.
So I was running the original alpha 1 gen 2 with a brand new impeller kit in it. that out drive never had any problems cooling the old over worked 5.0. One thing i noticed when installing the new impeller. there was some erosion under the impeller plate, there is a small aluminum wall that separates the water from the exhaust over the 20 years in service salt water has made a gape to were the impeller lower plate would not seal the air out. hard to explain I felt that i was getting air sucked into the cooling system at higher rpm and that was not allowing to cool at speed. So being a 95% offshore boat i felt i didn't want to jimmy rig it with jb weld or epoxy. So i bought a brand new mercury out drive. The new out drive i ordered with the recommended gear ratio for the new engine of 1.47 the old one was 1.62 So i was expecting posable prop change.
This morning set out to another near by lake to test. Engine fires up like it should, I let it warm up a bit wile idling away from the dock. then i hammer down to see what happens. First thing i notice was the lack of power getting up on plain, i kinda figured with the higher gears it wouldn't be as peppy. So heading across the lake at 33mph and boat temp was a consistent 175deg. ran it for 10 -15 min. Im thinking fixed, not so fast. Backed it down and was planning to do some trolling. The wife wanted to know how slow we were going to troll since the Kokanee like it slow. The temp quickly ran up to 185deg 195 and the little alarm started singing again. So we ran around the lake for another 1/2 hour temp was steady 175 when running. But quickly rose when under 1500rpm. I did bring the temp gun this time and everything seemed normal. Manifolds were never over about 110deg. Checked every hose and all seemed to just verify what my dash gauges were. telling me. When I got home i ran it on the ears and with a high flow unregulated hose spicket The temp again rose to 190 untill i bumped up the rpm to about 1500 to cool it back down.
So thats my story, sorry for the long read !
I have checked and double checked the routing of the cooling system. When the outdrive was off i had my Daughter put a hose in the gimble housing water inlet and checked flow buy taking hoses off. Nothing was clogged, unrestricted flow throughout. When running the new outdrive in the driveway there was plenty of water flow exiting out.
I feel like i have thrown a lot of good parts at this boat and it keeps kicking me in the butt.
Any suggestions would be much appreciated.
For you prop guys.... im running a 14.5 -17 four blade its getting me about 3800rpm at WOT 33mph. I need about 1200 more rpm to get to 5000 were mercury suggests. Top speed is not as important to me 30-35mph is fine. would rather have the mid range power for easy hole shots when weighted down with big fat guys and lots of ice plus better control in rough sea..
In April we bought a new bobtail 350 mag mpi..I installed it myself, ,also went with a full closed water cooling system. everything went smooth. first shake down run took the boat to a local reservoir. (Oh ya the boat, its the 2001 Bayliner trophy 23' lives on a trailer very clean boat ) So engine seemed to run real good for first 15 min wile checking for leeks ect.. i asked it to get up on plain. Plenty of power Jumped up out of the hole couldn't of slapped the smile off of my face. temps climbed quick with in 2 min alarm was singing, So i backed it down to a idle and temp came down quickly to about 175deg (dash gauges) i forgot the one tool that i really needed the temp gun. I did that about 5 times not letting it get to 190-195 before i would let it cool, hoping maybe a air bubble needed to be worked out. Very discouraged i put it back on the trailer.
So I was running the original alpha 1 gen 2 with a brand new impeller kit in it. that out drive never had any problems cooling the old over worked 5.0. One thing i noticed when installing the new impeller. there was some erosion under the impeller plate, there is a small aluminum wall that separates the water from the exhaust over the 20 years in service salt water has made a gape to were the impeller lower plate would not seal the air out. hard to explain I felt that i was getting air sucked into the cooling system at higher rpm and that was not allowing to cool at speed. So being a 95% offshore boat i felt i didn't want to jimmy rig it with jb weld or epoxy. So i bought a brand new mercury out drive. The new out drive i ordered with the recommended gear ratio for the new engine of 1.47 the old one was 1.62 So i was expecting posable prop change.
This morning set out to another near by lake to test. Engine fires up like it should, I let it warm up a bit wile idling away from the dock. then i hammer down to see what happens. First thing i notice was the lack of power getting up on plain, i kinda figured with the higher gears it wouldn't be as peppy. So heading across the lake at 33mph and boat temp was a consistent 175deg. ran it for 10 -15 min. Im thinking fixed, not so fast. Backed it down and was planning to do some trolling. The wife wanted to know how slow we were going to troll since the Kokanee like it slow. The temp quickly ran up to 185deg 195 and the little alarm started singing again. So we ran around the lake for another 1/2 hour temp was steady 175 when running. But quickly rose when under 1500rpm. I did bring the temp gun this time and everything seemed normal. Manifolds were never over about 110deg. Checked every hose and all seemed to just verify what my dash gauges were. telling me. When I got home i ran it on the ears and with a high flow unregulated hose spicket The temp again rose to 190 untill i bumped up the rpm to about 1500 to cool it back down.
So thats my story, sorry for the long read !
I have checked and double checked the routing of the cooling system. When the outdrive was off i had my Daughter put a hose in the gimble housing water inlet and checked flow buy taking hoses off. Nothing was clogged, unrestricted flow throughout. When running the new outdrive in the driveway there was plenty of water flow exiting out.
I feel like i have thrown a lot of good parts at this boat and it keeps kicking me in the butt.
Any suggestions would be much appreciated.
For you prop guys.... im running a 14.5 -17 four blade its getting me about 3800rpm at WOT 33mph. I need about 1200 more rpm to get to 5000 were mercury suggests. Top speed is not as important to me 30-35mph is fine. would rather have the mid range power for easy hole shots when weighted down with big fat guys and lots of ice plus better control in rough sea..