Mercruiser 350 over heating at hign RPM
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I’ve been dealing with a sporadic over heating issue for the past 3 years. The engine only over heats when on plane at higher RPMs. This year it’s consistent, which might be a good thing. Everything I have read it’s due to lack of water flow. This year I replaced the drive water pick up hose and the heat exchanger. Thought for you I had the problem beat, NO! New Mercmonitor shows coolant temp at 159* no wake zone on the river. Get up on plane and the temp quickly climbs to 170* putting the engine into limp mode. I’m in fresh water, but the boats first 5 years was in salt water (dock in a blackish river). What do I do next??
Engine:
2003 Mercruiser 350 MPI w/Bravo III (closed cooling)
What I have done:
Impeller (4 times)
New stainless plate for impeller
Belt
Thermostat
Removed risers and cleaned (not too bad)
Water pick up hose
Heat Exchanger
Removed all hoses looking for blockage
Comments
@raybo3 - Heat exchanger brand new
What I've been reading it points to the exhaust manifolds. Is there any way to check them without pulling them off?
@raybo3 - Heat exchanger brand new
What I've been reading it points to the exhaust manifolds. Is there any way to check them without pulling them off?
You've mentioned hoses, I'm assuming you checked in the power steering cooler?
As far as checking manifolds/risers. On my prior boat I took them apart at the manifold/riser connection to check them. Just have a new gasket & spare bolts. Mine were clean and easy to check.
Dream 'Inn III -- 2008 400 Express
those things aren't supplied with a constant velocity/volume of water- it is dependent on RPM- either pump... the raw water or the circulation... if you're moving enough water at low RPMs to maintain temperature but are losing the ability at high RPMs, it's either obstructed or it's not pumping enough...
these things don't have a heavy clutch fan hanging off of them like a car does, and that water pump bearing doesn't take abuse like a bad impeller because it's lacking that fan... the circulation pumps impeller could be worn to a nub and how would you know it? most likely because it loses it's ability to move necessary volume of water at high RPMs....
check your engines circulation pump.... I wager it's worn...
Boat Name: King Kong
"Boat + Water = Fun"
@69fastback - 170* goes into limp mode. I'm sure 170* wont hurt the engine but the temp is going in the wrong direction.
What if the exhaust manifolds are blocked by corrosion?
Faulty EMCT sensor?
i would start to get worried over 200
@F1100 - Thats what I'm thinking
@rasbury - maybe you are on to something
Maybe my water flow sensor is bad??
Dream 'Inn III -- 2008 400 Express
Boat Name: King Kong
"Boat + Water = Fun"
Boat Name: King Kong
"Boat + Water = Fun"
https://rinkerboats.vanillaforums.com/discussion/4039/are-my-raisers-running-to-hot-350-mag-mpi-2003-solved#latest