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hhagan posted 08-09-2009 10:31 AM ET (US)
My 2004 Mercury 115-HP FOURSTROKE is making oil. Have read a bit and talked to dealer. ~~The Question:~~
Is making oil a bad thing? Should the case be drained and underfilled? Is there a problem with leaving it as is?
jimh posted 08-09-2009 10:55 AM ET (US)
Making oil refers to the dilution of the crankcase lubricating oil in four-cycle motors. The lubricating oil is diluted and contaminated with combustion chamber blow-by, or with raw gasoline from other paths.
Lubricating oil which has become contaminated with gasoline and other combustion chamber blow-by products will not be an effective lubricant for your motor. You should drain the contaminated lubricating oil from the crankcase and replace it with fresh, uncontaminated lubricants.
When replacing the lubricating oil in the crankcase, the oil level should be maintained at the proper fill level as indicated on the dip stick when checking following the proper procedure.
Are you asking if you should intentionally use less lubricating oil in the crankcase of your Mercury FOURSTROKE engine so that when it becomes contaminated with gasoline and other combustion chamber blow-by products the level in the crankcase sump can increase to the normal fill mark? If so, then, no, do not intentionally fill the crankcase sump with less oil to allow for room for contamination to increase the level.
weekendwarrior posted 08-09-2009 11:51 AM ET (US)
Try to figure out why it's making oil to see if you can eliminate the problem. If it is because you spend most of your time at slow speeds then you might just have to increase the frequency that you change your oil to make sure the motor always has good undiluted oil.
hhagan posted 08-09-2009 10:35 PM ET (US)
We use the boat every other week for about 5 months out of the year, maybe longer. Usually running at cruising speed of 27 mph and 4500 rpm for 2 or 3 hours pulling tubes and zooming around. No trolling. We use a kicker for that. I generally change oil yearly and certainly do not have to add any. Would you suggest filter changes at more frequent intervals along with the oil?
jimh posted 08-10-2009 08:23 AM ET (US)
If your use of the motor is as described, I recommend you change your four-cycle outboard lubricating oil at 50-hours intervals instead of once a year.
hhagan posted 08-10-2009 12:44 PM ET (US)
OK to use high quality automotive oil, or should I stick with Mercury oils?
jimh posted 08-10-2009 08:22 PM ET (US)
If you are still in the warranty period, I recommend you use the recommended OEM branded oil. Using the recommended OEM oil makes any dispute about oil quality an unarguable point if there is a problem with the engine. The cost difference is not great compared with the total cost of ownership of the motor. If you shop around you can often find the OEM branded oil being sold at attractive prices.
There is often a corollary between operating temperature and crankcase oil contamination. If you do not have a temperature gauge for the outboard, you might consider investing in one so you can observe the operating temperature. The cooling system of outboard motors can be easily affected from small debris that enters the cooling system. Engines that run cold tend to have more problems with oil contamination than engines that run at their recommended temperature, which typically is 140-degrees-F to 160-degrees-F.
weekendwarrior posted 08-12-2009 11:26 AM ET (US)
Changing the filter won't help, the filter doesn't absorb gas.
All engines have some blowby. Normally engines "make oil" when the oil doesn't get hot enough to steam off the gas that collects in the oil from the blowby, such as during extended slow speed running. If your usage is as described then it is unusual that it would make oil. Checking things that would affect engine temp is a good idea. Maybe a thermostat is stuck open keeping the engine too cool? Check the crank case vent line to make sure it is not plugged. Do you have any cylinders running obscenely rich, such as from a stuck carb float? Did this problem start suddenly, or has this always been a trait of this motor?
Also are you sure it's gas in the oil? If it is water, the oil will most likely be milky just after use, but the water and oil would separate after sitting for a while with the oil on top.
weekendwarrior posted 08-12-2009 11:30 AM ET (US)
Oops just noticed I read your filter question wrong. I would change the filter at the interval recommended in the manual. The only reason I could think to change it sooner would be to prevent the diluted oil in the filter from contaminating the new oil.
Marlin posted 08-12-2009 12:44 PM ET (US)
I have a hard time believing that piston ring blow-by will accumulate to any meaningful amount in the crankcase. More likely there is a problem with the low-pressure fuel pump, which if I recall correctly is an engine-driven diaphragm pump. A diaphragm failure may result in raw fuel leaking into the crankcase. I'll try to remember to check my service manual tonight regarding that pump.
-Bob
hhagan posted 08-13-2009 07:41 AM ET (US)
Thanks for all the input. It is not my impression that the engine runs cold but checking the operating temp seems like a good idea. Where can a sensing unit be installed? Also, I have checked oil right after running engine and see no emulsified water so if anything is contaminating oil I suspect it is gas.
Marlin posted 08-13-2009 09:24 AM ET (US)
I checked my manual last night. The low-pressure fuel pump on this engine is a diaphragm pump mounted on the valve cover, and driven by a plunger that rides on the camshaft. If the diaphragm has ruptured, it could easily be introducing fuel into the valve cover.
The manual lists the fuel pump rebuild as "moderate" in difficulty, but looking at the diagrams, it doesn't look particularly scary.
-Bob
jimh posted 08-13-2009 09:35 AM ET (US)
Many outboard motors have a threaded boss machined into the upper cylinder head and into which a temperature sensor can be installed.
weekendwarrior posted 08-13-2009 10:53 AM ET (US)
If your fuel pump is such that a damaged diaphram could leak oil into the gas then given your use case that would be my number one suspicion. Blowby can definitely cause making oil, but making oil from blowby is unusual in a case where the motor doesn't spend a lot of time going slow. A pump leaking gas into the oil would definitely do it.
Tohsgib posted 08-13-2009 01:31 PM ET (US)
I was just reading Boating Mag and somebody was complaining about their F115 making oil. The mechanic noted that the engine's thermostat is very important. If the engine is not above or the EMM "thinks" the engine is not above 105 degrees it continues to dump fuel into the engine like a choke. This not only can get passed the rings but builds up carbon which escalates the problem.
seahorse posted 08-14-2009 04:55 PM ET (US)
Thermostat operation is very important on computer controlled engines. Yamaha 115 had similar problems and came out with a hotter thermostat kit and I think some other goodies to help combat "making oil".
Another cause is over-propping the motor or overloading the boat which makes the motor struggle. If the computer senses a lugging condition, it will deliver extra fuel to the cylinders to keep combustion temperatures in line. That extra fuel contributes to oil dilution.
towboater posted 08-15-2009 12:06 PM ET (US)
Interesting reading.
Even though the engine seems to run okay, would checking plugs and cylinder pressure reveal or eliminate a gasket [failure]?
hhagan posted 08-15-2009 11:40 PM ET (US)
Good talk with Merc tech at Conrad Bros Marine today. This engine has Yamaha power head. Both the 115 Merc and Yamaha 4 strokes have this problem. Leaking fuel pump not common. Cool running engine very common. My thermostat is a 122 deg open 140 deg full open. Tech is checking to see if warmer tstat is recommended by Merc to correct making oil problem.
SIM posted 08-16-2009 06:18 PM ET (US)
Excessive carbon buildup can also cause high cylinder leakage which can lead to blo-by and fuel dilution. To determine if this is the case, you would have to do a cylinder leak down test.
Propped so you are at 5800-6000 at wide open and make sure the engine t-stat is functioning correctly.

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Author	Topic: Mercury 115 FOURSTROKE Making Oil
hhagan	posted 08-09-2009 10:31 AM ET (US) My 2004 Mercury 115-HP FOURSTROKE is making oil. Have read a bit and talked to dealer. ~~The Question:~~ Is making oil a bad thing? Should the case be drained and underfilled? Is there a problem with leaving it as is?
jimh	posted 08-09-2009 10:55 AM ET (US) Making oil refers to the dilution of the crankcase lubricating oil in four-cycle motors. The lubricating oil is diluted and contaminated with combustion chamber blow-by, or with raw gasoline from other paths. Lubricating oil which has become contaminated with gasoline and other combustion chamber blow-by products will not be an effective lubricant for your motor. You should drain the contaminated lubricating oil from the crankcase and replace it with fresh, uncontaminated lubricants. When replacing the lubricating oil in the crankcase, the oil level should be maintained at the proper fill level as indicated on the dip stick when checking following the proper procedure. Are you asking if you should intentionally use less lubricating oil in the crankcase of your Mercury FOURSTROKE engine so that when it becomes contaminated with gasoline and other combustion chamber blow-by products the level in the crankcase sump can increase to the normal fill mark? If so, then, no, do not intentionally fill the crankcase sump with less oil to allow for room for contamination to increase the level.
weekendwarrior	posted 08-09-2009 11:51 AM ET (US) Try to figure out why it's making oil to see if you can eliminate the problem. If it is because you spend most of your time at slow speeds then you might just have to increase the frequency that you change your oil to make sure the motor always has good undiluted oil.
hhagan	posted 08-09-2009 10:35 PM ET (US) We use the boat every other week for about 5 months out of the year, maybe longer. Usually running at cruising speed of 27 mph and 4500 rpm for 2 or 3 hours pulling tubes and zooming around. No trolling. We use a kicker for that. I generally change oil yearly and certainly do not have to add any. Would you suggest filter changes at more frequent intervals along with the oil?
jimh	posted 08-10-2009 08:23 AM ET (US) If your use of the motor is as described, I recommend you change your four-cycle outboard lubricating oil at 50-hours intervals instead of once a year.
hhagan	posted 08-10-2009 12:44 PM ET (US) OK to use high quality automotive oil, or should I stick with Mercury oils?
jimh	posted 08-10-2009 08:22 PM ET (US) If you are still in the warranty period, I recommend you use the recommended OEM branded oil. Using the recommended OEM oil makes any dispute about oil quality an unarguable point if there is a problem with the engine. The cost difference is not great compared with the total cost of ownership of the motor. If you shop around you can often find the OEM branded oil being sold at attractive prices. There is often a corollary between operating temperature and crankcase oil contamination. If you do not have a temperature gauge for the outboard, you might consider investing in one so you can observe the operating temperature. The cooling system of outboard motors can be easily affected from small debris that enters the cooling system. Engines that run cold tend to have more problems with oil contamination than engines that run at their recommended temperature, which typically is 140-degrees-F to 160-degrees-F.
weekendwarrior	posted 08-12-2009 11:26 AM ET (US) Changing the filter won't help, the filter doesn't absorb gas. All engines have some blowby. Normally engines "make oil" when the oil doesn't get hot enough to steam off the gas that collects in the oil from the blowby, such as during extended slow speed running. If your usage is as described then it is unusual that it would make oil. Checking things that would affect engine temp is a good idea. Maybe a thermostat is stuck open keeping the engine too cool? Check the crank case vent line to make sure it is not plugged. Do you have any cylinders running obscenely rich, such as from a stuck carb float? Did this problem start suddenly, or has this always been a trait of this motor? Also are you sure it's gas in the oil? If it is water, the oil will most likely be milky just after use, but the water and oil would separate after sitting for a while with the oil on top.
weekendwarrior	posted 08-12-2009 11:30 AM ET (US) Oops just noticed I read your filter question wrong. I would change the filter at the interval recommended in the manual. The only reason I could think to change it sooner would be to prevent the diluted oil in the filter from contaminating the new oil.
Marlin	posted 08-12-2009 12:44 PM ET (US) I have a hard time believing that piston ring blow-by will accumulate to any meaningful amount in the crankcase. More likely there is a problem with the low-pressure fuel pump, which if I recall correctly is an engine-driven diaphragm pump. A diaphragm failure may result in raw fuel leaking into the crankcase. I'll try to remember to check my service manual tonight regarding that pump. -Bob
hhagan	posted 08-13-2009 07:41 AM ET (US) Thanks for all the input. It is not my impression that the engine runs cold but checking the operating temp seems like a good idea. Where can a sensing unit be installed? Also, I have checked oil right after running engine and see no emulsified water so if anything is contaminating oil I suspect it is gas.
Marlin	posted 08-13-2009 09:24 AM ET (US) I checked my manual last night. The low-pressure fuel pump on this engine is a diaphragm pump mounted on the valve cover, and driven by a plunger that rides on the camshaft. If the diaphragm has ruptured, it could easily be introducing fuel into the valve cover. The manual lists the fuel pump rebuild as "moderate" in difficulty, but looking at the diagrams, it doesn't look particularly scary. -Bob
jimh	posted 08-13-2009 09:35 AM ET (US) Many outboard motors have a threaded boss machined into the upper cylinder head and into which a temperature sensor can be installed.
weekendwarrior	posted 08-13-2009 10:53 AM ET (US) If your fuel pump is such that a damaged diaphram could leak oil into the gas then given your use case that would be my number one suspicion. Blowby can definitely cause making oil, but making oil from blowby is unusual in a case where the motor doesn't spend a lot of time going slow. A pump leaking gas into the oil would definitely do it.
Tohsgib	posted 08-13-2009 01:31 PM ET (US) I was just reading Boating Mag and somebody was complaining about their F115 making oil. The mechanic noted that the engine's thermostat is very important. If the engine is not above or the EMM "thinks" the engine is not above 105 degrees it continues to dump fuel into the engine like a choke. This not only can get passed the rings but builds up carbon which escalates the problem.
seahorse	posted 08-14-2009 04:55 PM ET (US) Thermostat operation is very important on computer controlled engines. Yamaha 115 had similar problems and came out with a hotter thermostat kit and I think some other goodies to help combat "making oil". Another cause is over-propping the motor or overloading the boat which makes the motor struggle. If the computer senses a lugging condition, it will deliver extra fuel to the cylinders to keep combustion temperatures in line. That extra fuel contributes to oil dilution.
towboater	posted 08-15-2009 12:06 PM ET (US) Interesting reading. Even though the engine seems to run okay, would checking plugs and cylinder pressure reveal or eliminate a gasket [failure]?
hhagan	posted 08-15-2009 11:40 PM ET (US) Good talk with Merc tech at Conrad Bros Marine today. This engine has Yamaha power head. Both the 115 Merc and Yamaha 4 strokes have this problem. Leaking fuel pump not common. Cool running engine very common. My thermostat is a 122 deg open 140 deg full open. Tech is checking to see if warmer tstat is recommended by Merc to correct making oil problem.
SIM	posted 08-16-2009 06:18 PM ET (US) Excessive carbon buildup can also cause high cylinder leakage which can lead to blo-by and fuel dilution. To determine if this is the case, you would have to do a cylinder leak down test. Propped so you are at 5800-6000 at wide open and make sure the engine t-stat is functioning correctly.