View Full Version : Overheating Marine Pwr 350 on LOW rpms

04-24-2004, 12:17 PM
" Hi, I've got twin 350 marine power engins and am getting high temps when I run my starboard engine at low rpms. When I come up on rpms the system cools down and then reheats as I drop in rpms again. I've run new coolant through the system and bubbled it out. The salt water system is pumping plenty of salt water through the exhaust system. It never actually "overheats" to dangerous levels since i keep a close eye on it and shut down immediately.
Any initial thoughs on what this might be? Thanks, Kevin "

Vincent Crawford
04-27-2004, 08:29 PM
check for clogged heat exchange

04-28-2004, 08:53 PM
" Ok I don't know if you figured it out yet since I am new.

The impellar in the raw water pump could be worn. The riser could be clogged. Or there may not be enough coolant in the heat exchanger. The water pump would be worn slap out.

I also have marine power engines. I would suggest pulling off the exhaust hoses and make sure the riser haven't built up to much crust. Clean them out with a coat hanger, screw driver or scraper. You may want to take them to a radiator shop and have them done like a radiator. They do a great job. Cheap too!!

The Thermostat may be bad. Pull it out first thing and reseal it with silicon, run it, and see if that cures the problem. If so, you may just need to replace the thermostat. I don't run with thermostats. I run most of the time at 140-150 range anyway which is the operating temperature of the engines. The only time I go below that is when I'm idling to the marina or trolling for a big one.

Hope that helps. "

Tom Brown
05-05-2004, 06:39 PM
" My 350 Mag Merc does the same thing, low rpm cooling problems. If the impeller isn't the problem and the thermostat has been removed, then is it most likely the "crust" in the system? "

01-29-2006, 05:16 AM
water may be getting in but if it cant get out you will have this problem

01-29-2006, 05:18 AM
also pressure check cooling system pull side covers on heat exchanger ispect w flashlight clean out tubes

02-10-2006, 12:34 AM
you also need to run that engine w/ thermostat in for system to function properly