4 stroke “making oil”

What you think?

I get a few customers each year with high oil levels in their 4-stroke outboards and it’s really tough to explain why sometimes. So I prepared this to present to customers with the problem and I thought it would make a good FAQ.

Q. Why does my 4-stroke outboard oil level keep rising? I never add any. Shouldn’t it be going down?

A. This is referred to as “Making oil”. Here it is in a nutshell. Water vapor enters the crankcase of all motors from the atmosphere, and as a by-product of combustion. In other motors, the oil gets rather hot and any water vapor that may condense will steam-off and exit the crankcase breather. 4-stroke outboard motor oil doesn’t get nearly as hot, so the water just keeps on collecting.

Q. Is it always water?

A. No. Tiny amounts of raw fuel also leak into the crankcase on the compression stroke, potentially diluting the oil and raising the level on a cool-running motor. Or there could be a fuel system leak. Typically the odor of the latter situation is fairly obvious, but not necessarily. Lack of a gassy smell shouldn’t preclude checking the possibility of fuel system leaks. Over choking and frequent flooding will also cause fuel to get into the oil.

Q. Where does the water come from?

A. Three sources. Asmosphere, combustion and fuel. There’s always moisture in the air, especially near bodies of water. Some condenses out naturally and collects in the crankcase of a sitting motor. Some comes in right along with the air as it runs. The body of water you’re operating on produces a lot of atmospheric water vapor, especially a few feet above the water line … where the powerhead is.

H20 is one of the compounds that forms when gasoline is burned, along with CO, CO2, NOX, etc. Some leaks into the crankcase right along with the other contaminants and mixes into the oil. Alcohol combustion makes mostly CO2 and H2O, so alcohol-blended fuels tend to produce more water vapor than straight gasoline.

Q. Wouldn’t my oil turn milky if water was in there?

A. Eventually it will. But oil has some capacity to retain water and it eventually reaches a threshold where it starts to cloud.

Q. Why doesn’t the oil get hot enough to steam it off?

A. It can. If the motor is running hard enough to plane the boat, water that otherwise cools the oil isn’t splashing on the sump that holds the oil. But boats that are run at non-planing speeds may not heat the oil up very much at all. The water the boat is running in cools the oil which is in the sump beneath the powerhead. That water can keep the oil pretty cool just by splashing against the outside of the aluminum sump.

Motors that are mostly operated at sub-planing speeds seem to be especially susceptible to making oil. Many times the complaint is that a kicker used for trolling has the problem, but the main motor doesn’t. That’s because the main motor is used to get to the fishing spot fast to troll slow with the kicker. One is hot, the other is not.

Q. Why is it a problem with my motor and not my neighbor’s?

A. Two things really aggrivate the problem. Cool running temperature of the oil, and the abundance of moisture available that inevitably collects. The environment the boat is kept in, water temperature, the fuel you use, and the way you operate the motor have huge effects on whether or not this is going to be a problem.

Q. Wouldn’t a hotter thermostat solve the problem?

A. Doesn’t help much, but it helps. Problem is that you’re regulating coolant temperature and not oil temperature. The oil will get a little warmer as a result, but the powerhead will be running hotter and that’s probably not good. Then consider that if the sump is getting splashed by water, that pretty much cancels it out.

Q. How can I be sure of what is making the oil?

A. You can have the oil analyzed. There are many labs that test automotive oil. Outboard readings may not be consistent with what would be expected from an automobile engine, so interpreting the data could be problematic. But it sure will show what is in the oil. A quick search yielded a lot of labs offering this service through the mail for a wide range of prices. Shop around, but it could be money well invested. One site with abundant information is http://www.bobistheoilguy.com/ They also have a Forum if you have any questions.

Q. So what can I do about it?

A. Right now, the approach is to minimize the amount of contamination allowed to enter. That means keeping the motor as unexposed to atmospheric moisture as possible. Practical in some situations, impossible in others. The manufacturers are also stressing proper and agressive break-in procedures to mate surfaces better and keep leakage into the crankcase (blow-by) to a minimum. Avoid alcohol-blended fuels if you can. Finally, allow the motor to get hot enough to steam-off what water will inevitably collect in there. That’ll probably mean running it hard for awhile. (If your lake has a speed limit … Ouch!)

If all of that fails, have the motor checked for gasket leakage. It could be coming from the cooling system. More frequent oil & filter changes may be necessary. But try running the motor hard for several minutes every time you go out. That’s the easiest, cheapest, and most enjoyable thing to try.

Q. So you mean I HAVE to open it up and go fast once in awhile?

A. Dang shame, ain’t it?

Very interesting post, and thanks for the info. What about my 15hp Yammy 4 stroke? You’re saying I should just open that up a little bit too once in a while?

I just noticed this was happening to my kicker yesterday. Thanks for the info. Now I know whats going on with it.

I was told to run it hard after break in to seat the rings well in the cylinders.

No problems with my 4 stroke.

I was told the same thing about running it hard late in the break-in period to seat the rings…..my rig has 170 hours on it now and has never made oil as they call it.
I also am running Amzoil synthetic oil in the JohnSuzuki 140

Wait until its good and seated (no more making oil)before you switch to synthectic oil if you go that route.

Good post!

My 2006 Merc 115 4-stroke had a vac line that runs right through the fuel pump sump. It had cracked and eventually broke and sucked so much fuel into the bottom cylinders that it hyrdo-locked the motor. I thought it was a bad starter since it cracked the starter mount aluminum. Replaced that still wouldn’t turn over. Tried turning over with a ratchet on the flywheel locked. So now I thought I seized the motor. Luckily I found an obscure posting that discussed the hydro locking and being caused by a fractured vac line that runs right through the fuel in the fuel pump. When the hose fractures (btw it happens slowly)it sucks the fuel into the lower cylinders. Now imagine this happening slowly over time and that fuel diluting your oil (making oil). So I pulled my fuel pump and openned it up and sure enought the hose which for some reason runs right through the fuel in the fuel pump had completely ruptured. Next, I pulled the spark plugs and sure enough raw fuel ran out of the bottom 2 cylinders(which would suck the most fuel in based on the air intake feeding those more via gravity. I turned the motor again with the ratchet and shot fuel about 10ft out of the bottom cylinders. Next I changed the oil which was diluted and you could smell gas. I called Mercury and asked about this issue and they said a new replacement line was available (of course they would charge me for it) that was resistant to ethanol (clearly a design defect). I bought the boat/motor used and it was out of warranty, but of course Mercury was not help fixing their serious design flaw. I then happened to notice the air filter had completely deteriorated and of course a completely different metal replacing the original foam was available for about $40 (to fix Mercury’s other design flaw) in this motor.

So now 6 years later and after changing oil often to make sure the oil was oil and not diluted by gas I’ve been able to enjoy the motor. Other than this issue, (which would have cost thousands I’m sure at a dealer to fix) works correctly. My point for this “making oil” thread is that you may want to be aware that there is a vacuum hose running through many of the fuel pump housings that was a design defect and as it deteriorates could be adding fuel to your oil. Luckily my motor runs great and shows no sign of damage. I can hit 45mph still in a 17ft Lund and the motor stars and runs very quiet and smooth.

During winterizing dealer said my oil was milky. They said my thermostat was stuck open and engine running cool on short runs.

Improper break in can lead to a motor that makes oil all the time. The rings need to be set and high heat and load sets the rings. Fuel in the oil is the enemy of four stroke outboards. Make sure and run them wide open often. If you troll with a four stroke you need to change your oil more often not at 100 hours. Many people think that idling around is easy on a four stroke when it actually is the worst thing you can do to your motor.

Great post Thanks

I have had 5 4strokes, and have never ever seen water in the oil, on an engine that doesn’t have something wrong and fixable. Also have helped a couple of friends change their oil on their 4strokes, never water in the oil. On one of my friends, he had some fuel in the oil once, but never water. Also had a vacation house on the gulf for about 5 years where my boat sat on a lift over the humid gulf intercoastal, for that whole 5 years, sometimes not run for the 6-7 months straight that we were gone with no water in the oil from the moisture in the air. When living in that saltwater environment, and following the boating forums there, the only time that water moisture in the oil was an issue, was with people with bad thermostats, and faulty thermostats are a frequent issue there, especially when the engines weren’t fully flushed out after every use. Fuel in the oil seems to be an issue at times for some users, and the traditional thought is that they need to be run hard after the first few hours of break in to help seat the rings. Some will advise that you have to run it wide open for 20-30 minutes straight, or it wont break in. Show me where any factory recommends that. Not only is that unnecessary, but outright dangerous in the waters that some users are in. If you feel that you need to heat it up and run hard for a bit, of which I somewhat agree with, your engine will not know the difference between 5000 rpm and 5700-6000 rpm, and that can be done safely, accomplish the same thing, and probably be better for the long term reliability of your engine. Just think about it, commercial fisherman in the salt water market, will run their big Yamahas all day, put massive hours on them that even guides around here don’t begin to do, virtually never run them wide open, and have never considered any special break in, yet moisture isn’t a problem, and I almost never read about them in the forums there, making oil. If a mechanic were to tell me there was water in my oil, and there was nothing wrong with the engine, I would ask them to prove it. That might be tough for them now days as many of them now use a suction machine to change the oils, and if so, your oil is mixed with someone elses. I will add though, that I almost always run no ethanol gas, probably about 95% of the time.

I have a 2018 20 HP Tohatsu Outboard. When changing the Oil today about 2 quarts of water came out before I started getting any oil . This seems like bore than a “little condensation”. Does anyone have any suggestions as to what could be causing this? THanks

Someone resurrected a 2006 post in 2020, and now it’s turned into a first-time poster trying to make us believe he drained 2 quarts of water out of his Tohatsu 20 HP.

Does not mean he does not need help, he probably did a Google search that led him to the post…

If you found that much i would be looking for a bad head gasket, cracked block or water jacket. Compression or leakdown test could help isolate the bad cyl.

That’s exactly what happened. I have a problem , GOOGLED it and ended up here .

I was hoping for help and NOT to be insulted.

That being said, what Mark said is good advice to start to figure out the issue. Sorry for the other reply.

William Montanari wrote:

That’s exactly what happened. I have a problem , GOOGLED it and ended up here .

I was hoping for help and NOT to be insulted.

2 quarts of water? And it actually ran?

Well about a year back it ran rough so I checked the oil and noticed it was “Milky” so I stopped running it. It just sat until now because I had other priorities medical and business. A week back I was on the dock and noticed an oil slick coming from my boat so I decided to pull it out, which took some work because I don’t have a trailer and it’s a Pontoon Boat. After getting it out I checked the oil and when I pulled the plug around 2 quarts of water came out before the Oil began to flow. I read about these things “Building Oil” due to condensation etc but this is nuttssss. The boat is on a small lake 50 acres so it rarely is run wide open usually I just Troll. Probably the worse use I could imagine for a 4 stroke motor but I had no idea.

Is this 20hp your main engine or is it a kicker?

I have a 9.9 Tohatsu kicker that I found quite a bit of water in the oil (not 2 quarts!) after I left it in the down position and drug it through the water at 30 mph for an embarrassing number of miles. I took it to the dealer and they checked it over and found nothing wrong other than the diluted oil. It has continued to run fine for me for six years since without any more oil issues so it had to have been the dragging it at high speed that caused the dilution.

William, I sent you a PM

The “Making oil” was on my last motor, my problem was getting gas into my oil probably from the rings not being seated properly when new, I bought this motor used with the boat.
With that much water I would think you have a mechanical issue that needs to be addressed. I would have someone that knows what’s going on take a look at it before boating season. good luck and update us on what was found.

When I bought my Skeeter the seller switched props on me to a 26″ 3 blade. Way too much prop for the F250 and 21′ Skeeter. I started “making oil”. Apparently lugging the motor was pushing fuel into the crank case. Swapped out for a 19″ 4 blade Merc prop and it hasn’t happened since. Mush better hole shot too.

Dealer told me to run the Yamaha oil. If you have motor issues the first thing they do is have the oil tested. Also I was told that the Yamaha oil was rated take up to 20% fuel contamination before lubrication issues.

Thanks I’m unsure which Prop I have but it came with the motor. I’ll check it out

Thanks. Now that it’s out of the water having someone look at it will be easier.

This is the Main Motor and usually I just put/troll around. The LAke is only 50 acres so Wide open I’m on the other side in like 2 minutes. Then I just put along and fish.

UPDATE… Just called Tohatsu. They said the original Issue of Milkyness in Oil was probably from condensation BUT the 2 Quarts of Water coming out when I Pulled the Oil Plug was most probably from sitting UNCOVERED for a year and a half, in the Tilted Up position, which unbeknownst to me is a No No.
Their recommendation… Change the Oil Run it in a Bucket for awhile and see what happens. Incidentally they said running with ears would burn up the impeller and said the preferred method is in a Bucket with a Hose running.
THanks for the helpful comments and suggestions. I’ll Post the Outcome.