When a MerCruiser engine overheats, catastrophic damage to the engine will occur if the cause isn't repaired immediately. Repairing overheating issues requires inspection and testing of both mechanical and cooling system parts.
The following service procedures will guide the mechanic in identifying overheating causes associated with the 496 C.I.D MerCruiser engines, and possible remedies. Exact model years include: 2001 2002 2003 2004 2005 2006 2007 (MCM) Models: 496 Mag HO (Serial Number 0M000000 & Up), 496 Mag (Serial Number 0M000000 & Up), Inboard (MIE) Models, 8.1S HO (Serial Number 0M000000 & Up), 8.1S Horizon (Serial Number 0M000000 & Up)
Engine Mechanical Overheating
The following lists common causes for mechanically overheating issues and possible remedies. It's important to realize that one or more issues may be causing the engine to overheat.
- At WOT (wide open throttle), the engine RPM is lower then factory Specifications. Inspect for damaged or incorrect sized propeller; False bottom (or hull) filled with water; or excessive growth growing on the bottom of the boats hull.
- Check for lean fuel mixture, engine running to lean.
- Check the spark plugs heat range, replace if necessary.
- Check exhaust system for restrictions (clogged or bends caused by damage).
- Check if the valve timing is off (incorrectly installed timing chain or timing chain jumped).
- Inspect engine for blown head gasket(s). Performing a compression test normally cant determine if a head gasket is blown as pressure must build to expose head gasket leaks. MerCruiser engines will usually not overheat when operating at normal temperatures, and at low RPM. Head gasket leaks are usually exposed once the engine speed exceeds 3000 RMP.
- Check for adequate lubrication to the engines moving parts (e.g. damage oil pump, oil level low or oil passages clogged).
Cooling System Overheating
Before testing the engines cooling system, first determine if the engine is actually overheating, or if the temperature gauge or sender is working properly. The easiest way to test the gauges is to install new parts.
NOTE: The following inspection procedures may not apply to some model year MerCruiser engines as some models are not equipped with the same parts.
- Inspect the drive belt for looseness or damage.
- Inspect the shutoff valve on the seawater pump/pickup assembly (if equipped). Check if the valve is closed or partially open.
- Inspect all hoses between the seawater pump inlet and seawater pickup. Check for loose hose connections. If loose connections exist, the pump will suck in air or fail to prime, subsequently, forcing air pockets into the cooling system. This step only pertains to models equipped with a belt driven seawater pump.
- Kinked, collapsed or damaged seawater inlet hose.
- Obstruction in seawater pickup.
- Blockage or entity causing water turbulence on the bottom boat hull. Inspect bottom hull, before seawater pickup. Water turbulence in front of the pickup will cause air bubbles to be sucked into the cooling system.
- Text thermostat, replace as needed.
- Check exhaust elbow water outlet holes for possible blockage.
- Determine if the seawater pump is defective (e.g. excessively worn pump impeller).
- Engine's circulation pump possibly faulty.
- Blockage somewhere in cooling system (e.g rust, salt deposits, casting flash). To get a better understanding of items to be serviced in the engines cooling system, refer to the water flow drawing in the factory repair manual.
NOTE: If the MerCruiser engine is equipped with a closed cooling system, inspect the items mentioned above, and the following:
- Coolant level is low, fill as needed.
- Incorrect mixture of water and antifreeze. The correct antifreeze ratio is 50/50 and shouldn't exceed 60% antifreeze and 40% water.
- Check the heat exchanger cores for blockage.
- Water hoses installed incorrectly or reversed (water distribution at engine block). Reference the correct year factory repair manual for your model and year.
It's highly recommended you refer to the factory repair manual when attempting to diagnose engine overheating problems. Remember, if the MerCruiser engine runs to hot, serious damage will occur. Do not put the motor back into service until the issue is resolved.
Common Overheating Searches
- mercruiser overheating troubleshooting
- mercruiser overheating problems1978
- mercruiser 3.0 overheating problem
- mercruiser overheating at idle
- mercruiser 4.3 overheating problems
- mercruiser 496 engine overheating
- 1995 cruiser 2470 overheating troubleshoot
- 350 mercruiser overheating
- 8.1s horizon overheating
- common overheating problem 5.0 mercruiser
- does a full bilge in a mercruiser cause overheating
- drive shower not working 496 overheating
- how to fix overheating 5.0l mercrusier
- how to fix overheating problem on mercruiser 7.4 inboard
- merc 454 horizon overheating at high rpm
- merc 470 overheating
- merc 5 liter smoke after over heating
- merccruiser overheating diagnosis
- mercruise 3.0 running hot problem
- mercruise 5.7l engine over heats
- mercruiser 1,7 dti overheat
- mercruiser 190 hp 4 cylinder is overheating
- mercruiser 3.0 how to tell if engine is overheating without temperature gage
- mercruiser 3.0 l one cylinder overheating
- mercruiser 3.0 litre can a cracked head cause overheating
- mercruiser 3.0 litre overheating at idle
- mercruiser 3.0 overheating could it be the thermostat
- mercruiser 3.0 overheating when opening up throttle
No comments:
Post a Comment