2002 Mercury 90-HP FOURSTROKE: Water in Oil Sump

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Author Topic:   2002 Mercury 90-HP FOURSTROKE: Water in Oil Sump

Whalering Since 74 posted 11-12-2008 02:46 PM ET (US)
Re 2002 Mecury 90-HP FOURSTROKE on Montauk 17:
I was advised by my mechanic that he found some water in the oil pan of my 2002 Mercury 90-HP FOURSTROKE stroke when he was checking the oil during winterizing. I've had no problems with the engine. It gets normal use, mostly weekends in the summer in all saltwater.
I fear a leaky head gasket, or head corrosion - neither a cheap fix. Any similar experiences or solutions?
OEB
95Outrage17 posted 11-12-2008 09:08 PM ET (US)
Hi OEB,
While unlikely, it is possible your Mercury has a corrosion problem. I have seen this problem with an 2001 Yamaha F100 which has the same powerhead as your Mercury. The use and service history was not known for that engine and a factory defect was also a possible cause. Regardless, the engine did not run properly and that is how the problem was discovered. Is your mechanic confident that it's water in the oil and not fuel? How often have the anodes in the cylinder head and water jacket been replaced? How often is the engine oil changed? Is the boat left in the water during the boating season and if so, is the motor left down or tilted when not in use? Your mechanic likely removed your spark plugs to spray storage fogging oil into the cylinders. At this time did he notice any evidence of water fouling on the spark plugs? If any cylinder shows signs of a problem, it would likely be the bottom cylinder.
I doubt you have a corrosion problem though, it's not common. I would do more investigating to determine the cause. Has the engine's compression been checked reciently?
As a note; I have the 2004 version of your motor on my Outrage and I've been quite pleased with it. Lots of saltwater hours on it.
- Chris
jimh posted 11-13-2008 08:54 AM ET (US)
Do you have a temperature gauge on the motor? Does the motor reach 140-degrees-F, the normal operating temperature range?
95Outrage17 posted 11-13-2008 06:05 PM ET (US)
Good point. The thermostat failed last fall in my motor. My main indicator was my temperature gauge. Other then that it ran a little rough occasionally if I remember correctly. I believe most Montauks of that vintage did not have a temp gauge installed at the factory. The '03 170 in my driveway does not have one, instead a water pressure gauge. Actually I should probably check it's thermostat, they're easy to access on those engines. Just need a 10mm socket.
- Chris

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Author	Topic: 2002 Mercury 90-HP FOURSTROKE: Water in Oil Sump
Whalering Since 74	posted 11-12-2008 02:46 PM ET (US) Re 2002 Mecury 90-HP FOURSTROKE on Montauk 17: I was advised by my mechanic that he found some water in the oil pan of my 2002 Mercury 90-HP FOURSTROKE stroke when he was checking the oil during winterizing. I've had no problems with the engine. It gets normal use, mostly weekends in the summer in all saltwater. I fear a leaky head gasket, or head corrosion - neither a cheap fix. Any similar experiences or solutions? OEB
95Outrage17	posted 11-12-2008 09:08 PM ET (US) Hi OEB, While unlikely, it is possible your Mercury has a corrosion problem. I have seen this problem with an 2001 Yamaha F100 which has the same powerhead as your Mercury. The use and service history was not known for that engine and a factory defect was also a possible cause. Regardless, the engine did not run properly and that is how the problem was discovered. Is your mechanic confident that it's water in the oil and not fuel? How often have the anodes in the cylinder head and water jacket been replaced? How often is the engine oil changed? Is the boat left in the water during the boating season and if so, is the motor left down or tilted when not in use? Your mechanic likely removed your spark plugs to spray storage fogging oil into the cylinders. At this time did he notice any evidence of water fouling on the spark plugs? If any cylinder shows signs of a problem, it would likely be the bottom cylinder. I doubt you have a corrosion problem though, it's not common. I would do more investigating to determine the cause. Has the engine's compression been checked reciently? As a note; I have the 2004 version of your motor on my Outrage and I've been quite pleased with it. Lots of saltwater hours on it. - Chris
jimh	posted 11-13-2008 08:54 AM ET (US) Do you have a temperature gauge on the motor? Does the motor reach 140-degrees-F, the normal operating temperature range?
95Outrage17	posted 11-13-2008 06:05 PM ET (US) Good point. The thermostat failed last fall in my motor. My main indicator was my temperature gauge. Other then that it ran a little rough occasionally if I remember correctly. I believe most Montauks of that vintage did not have a temp gauge installed at the factory. The '03 170 in my driveway does not have one, instead a water pressure gauge. Actually I should probably check it's thermostat, they're easy to access on those engines. Just need a 10mm socket. - Chris