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3.0L overheating

F

fyoung33

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Cannot solve overheating problem on my 3.0L 140R engine with Mercruiser Sterndrive. Rebuilt the sterndrive pump last year and it puts out plenty of water flow to the engine. Put on the earmuffs in the driveway and water temp will stabilize at 140 deg. F. Plenty of coolant flow exiting the sterndrive. Took it out in the river and water temp will stabilize only below 2000 RPM, which is before the boat is even on plane. Once RPM exceeds 2000, the water temp continues to rise. Put the boat up on plane and run @ 2500, the temp continues to climb and within minutes is heading north of 230. Removed thermostat just to make sure it's not the issue and there was no change. Checked all hoses, engine water pump, and cannot find any issue. The engine water pump is original and appears to be in good condition. This boat is a 17' bowrider and used in fresh water only. Any ideas? Thank you. Fred
 
2 things to check, does the hose from the circ pump to the T Stat get hard with the rpm?
Yes, clogged,restricted riser.
High speed overheats always start with the impeller, recheck your work. Including the base of the pump
 
Thanks BT Doctur. I will try the hose test next time out on the water. As far as the impeller, are you referring to the sterndrive impeller?
 
I give up! LOL
2012 EFI low emission 3.0L Engine overheats and alarms on the water. Gauge shows about 10 mins past 12 O clock on the gauge. No temps shown just a semi circle from 9AM to 3PM so midday 12 is normal. New impeller December last year. I pulled the thermostat, dropped in boiling water and it opened OK.

On pontoon ramp. Muff on hose pressure and thermostat out it runs cool, say 10 o clock. So new thermostat, 160deg and... over temp again. Pulled the poppet valve assy, rusty but normal and free to move. Checked temp sender with meter Ok according to specs 10-250 ohms.
Water exhaust out of the transom is warm only not hot so here i am.

2nd issue lately is a brief 1 second alarm every 60 seconds when running within normal parameters. 3.5k revs, (Max revs 4500) all gauges normal. good oil pressure temps normal, battery charging at 13.8. All fluid levels are fine, engine, steering, tilt etc.
 
Bravoone 3l said:
I give up! LOL
2012 EFI low emission 3.0L Engine overheats and alarms on the water. Gauge shows about 10 mins past 12 O clock on the gauge. No temps shown just a semi circle from 9AM to 3PM so midday 12 is normal. New impeller December last year. I pulled the thermostat, dropped in boiling water and it opened OK.

On pontoon ramp. Muff on hose pressure and thermostat out it runs cool, say 10 o clock. So new thermostat, 160deg and... over temp again. Pulled the poppet valve assy, rusty but normal and free to move. Checked temp sender with meter Ok according to specs 10-250 ohms.
Water exhaust out of the transom is warm only not hot so here i am.

2nd issue lately is a brief 1 second alarm every 60 seconds when running within normal parameters. 3.5k revs, (Max revs 4500) all gauges normal. good oil pressure temps normal, battery charging at 13.8. All fluid levels are fine, engine, steering, tilt etc.
Click to expand...
are you sure it is a over temp alarm, i think drive lube and oil pressure can do that too.

If it is over temp are you using it in salt water and if so have you checked the manifold and riser for blockage
 
Thanks for the reply.
Yep, salt water and fresh water run every time i pull it out as it sits on a pontoon with winch.
I changed out the manifold 60 hours ago with the new one Merc recommended as it has larger water jacket clearance for salt operation.
Thought about blockage but with the thermostat out it runs so cool it barely registers on the temp gauge and the exhaust water is only just barely warm. I've ordered a new temp sensor and see if that makes any difference.
Oil pressure is great it seems, about 3/4 way to max. Again gauge has no numerals so unable to actually measure without putting a T piece in and running a pressure line to a calibrated pressure gauge. Can't check the lube oil as on the ramp it's tilted up. Will have to borrow a trailer sometime.
 
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