1978 mercruiser 350 260 hp gets hot around 4000 rpm I can run 3400 rpm all day stays below 160 as soon as I get close to 4000 rpm it goes up over 200. running 3400 rpm with it trimmed out making sharp turn it goes over 200 once it starts up you cant stop it. I changed the thermostat no help. Any ideas will be welcomed thank you.
350 getting hot
- Thread starter bobby777
- Start date
- Joined
- Jul 27, 2001
- RO Number
- 5508
- Messages
- 1,243
almost always it’s one of two things - not getting enough water pumped in - typically due to worn out impeller in the drive, or not getting water out, typically due to clogged exhaust components. this write up may provide some useful troubleshooting information...
www.boatered.com
Marine Engine Cooling System Troubleshooting
TEMPERATURE PROBLEMS WARNING: IF A TEMPERATURE PROBLEM IS SUSPECTED, BE CAREFUL. THE COOLING SYSTEM CONTAINS HOT LIQUID UNDER PRESSURE AND A CARELESS OR THOUGHTLESS ACTION COULD RESULT IN SEVERE INJURY. TEMPERATURE GAUGE PROBLEMS Before spending any time trying to diagnose a temperature...
www.boatered.com
- Joined
- Jul 27, 2001
- RO Number
- 5508
- Messages
- 1,243
how old is your raw water impeller? In my experience, water intake problems don't usually get worse when rpms increase - as the additional rpms allow a worn impeller to function well enough - so yours looks more like an internal blockage problem. But the fact that adjusting drive trim and turning changes things -- that makes my guess that the impeller is deteriorated.
