RandyJ
Master Chief Petty Officer
- Joined
- Jun 13, 2002
- Messages
- 808
I have two boats with chevy 350/260 mercruiser(both were built around 1976-1978). Both are doing the same thing...run hot when at high rpm. I can cruise at 3,000 or so rpm and stay around 160 or less. At 4,000-4,500 the engines will top 180 and be at 200 degrees in no time. The big boat (24' bayliner monterey cabin cruiser) has a relatively new long block, both engines have clean new exhaust manifolds (log type). The big boat is so heavy it really heats up fast. Too, it has a 470 (1.98) outdrive (originally 260s were coupled to a 1.5 outdrive). The big boat is hardly moving at 2,000-2500 rpm and I have to get up around 4,000 rpm to get speed just to stay up with the traffic on the lake. but over 2,000 rpm the ski boat (20'hammond) is zooming fast enough to pull skiiers with ease. I'm thinking I need more of a low speed type outdrive on the big boat because it is taking too much of a bite out of the water with the 1.98 gear ratio.... however, I just feel that both boats are unreasonably overheating. I'm a good mechanic and have been through both engines and boats very well. Big boat sounds like a loaded train trying to get a big load moving and vibrates alot around 2,500 but smooths out once speed is up. Ski boat just jumps out of the water and hauls tail....somebody help me think about this.
