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Author Topic:   4-Stroke Engines: "Making Oil"
jimh posted 03-23-2003 11:30 PM ET (US)   Profile for jimh   Send Email to jimh  
Apparently certain 4-stroke engines like the Yamaha/Mercury 90-HP are getting a reputation for "making oil."

The term refers to the situation where the level of the oil in the lubricating oil sump increases over time as a result of being contaminated by gasoline that has blown by the piston rings of the cylinders.

It seems that this problem is most apparent in a new engine during the break-in period and on engines which are run at low temperatures, keeping the contaminated oil from boiling out the gasoline.

Has this been a problem in any of the 4-stroke engines owned by our Whaler audience?

Bigshot posted 03-24-2003 09:55 AM ET (US)     Profile for Bigshot  Send Email to Bigshot     

You will smell the gas if it is in the oil by smelling the dipstick. In order for gas to get passed the rings a few things have to happen. First is the rings are worn but usually that will cause it to smoke. 2nd is a carb or injector(leaking) is bad causing the cyl(s) to fill with gas when engine is shut down and slowly weep past the rings over time. Rings are designed to hold back oil, not gas. If the engine is started while this gas is in the cyl(s) the compression may blast it by the rings on startup. Or a bad intake manifold gasket etc. Gasoline getting into your crankcase does not just "happen".

PMUCCIOLO posted 03-24-2003 01:19 PM ET (US)     Profile for PMUCCIOLO    

After reading this post last night, I corresponded with one of my friends who practices in Alaska. His welded aluminum fishing boat is powered by a 75HP Mercury 4-stroke. As he uses the boat for both business (travelling to see patients in his locum tenens agreement) and pleasure (fishing and sightseeing), he has logged over 300 hours on the motor in a little over one year.

He reports not ONE [his emphasis] problem with the engine. He says that he'll check in with the owner of some of the local fishing lodges, all of whom are converting to or have converted to four-stroke power.

Has any similar situation been described with four cycle automobile or aircraft engines operating in frigid climates? Would this situation be unique to gasoline engines, or would diesels be affected as well?

My technical knowlege in this field is limited, but it would seem that only a malfunction would create the situation you've described.


weekendwarrior posted 03-24-2003 04:55 PM ET (US)     Profile for weekendwarrior  Send Email to weekendwarrior     
I was chatting with the mechanic at the local dealer the other day on a somewhat related topic and he mentioned motors making oil. He mentioned to me that he sees this a lot on motors that were not broken in properly (the rings did not seat properly). I've also heard of it happening on motors that are used at slow speeds and don't get to full operating temperature for extended periods of time. Additionally I've seen this mentioned in Haynes and Clymer manuals for cars, commenting that this may be a problem in cars that are driven mostly at slow speeds and/or on very short trips in the city. In this case it is also recommended that the oil be changed more frequently.

dgp posted 03-24-2003 06:34 PM ET (US)     Profile for dgp  Send Email to dgp     
jimh, is this just "dock talk" or do you have a resource for documented information?
Alot of factors come into play here; oil level at drain interval, brand of oil, fuel consumed, hours of operation and angle of engine when checked.
Surely you're not trolling here!
PMUCCIOLO posted 03-24-2003 06:53 PM ET (US)     Profile for PMUCCIOLO    

dgp raises an interesting point. Did lhg put you up to this? JUST KIDDING! His recent posts seem to be critical of four-stroke power, and he clearly expresses brand loyalty to Mercury.


jimh posted 03-24-2003 09:58 PM ET (US)     Profile for jimh  Send Email to jimh     
Naw, no trolling or ulterior motives. I was just reading some chatter online about this.

On the Yamaha/Mercury angle I found it funny that the original complaint I read about this kept referring to the engine as a Mercury 4-stroke. But the problem is in the powerhead
and that is from Yamaha!

When people talk about how great their 4-stroke Mercury engine is, there is always a mention of "Oh yeah, but that is a Yamaha engine." Then when there is a problem it goes back to being a "Merc."

From the results so far seen here, it does not sound like this is a widespread problem.

Honda outboard were also mentioned in this context, too.

The usual cure suggested from the dealers is to change the thermostat for a higher temperature, getting the engine to run hotter. I guess that helps to boil off any water or fuel in the lubricating oil sump.

Another comment I read mentions changing the crancase oil more often, as often as every 50-hours. I guess some people like to work on their engines a lot.

SuburbanBoy posted 03-24-2003 11:54 PM ET (US)     Profile for SuburbanBoy  Send Email to SuburbanBoy     
As hard as this will be to believe, I owned a Suzuki TL1000 two cylinder, 1,000cc, fuel injected motorcyle. It was not programed properly (bug in the ECU routine) and it would quickly dilute the oil with gasoline. It would only take about 75 to 150 miles. The bike was recalled and the ECU was swapped out. This eliminated the mini refinery in the crankcase. This was a well documented flaw of that model Suzuki.


gss036 posted 03-25-2003 12:49 AM ET (US)     Profile for gss036  Send Email to gss036     
I had that problem with my Honda 15 HP, (making oil). I went to the dealer and he said the same as above, selling me a new (stainless ?)thermostat for $75.00, which only lasted about 3 weeks ( stuck open) and I to really push to get him to warranty it. At any rate, the new thermostat seems to work ok and it doesn't do it quite as bad. I use my Honda as a trolling motor, it is run at slow speeds for hours, like 6 hours today.
Yamaha has a real serious problem with gas in the oil on the early model (89-90) of the 9.9 hp high thrust 4 strokes. I had 3-4 friends who were given exchanges when theirs seized up because of the high gas content in the oil.
I change my oil about every 25-30 hours just to be safe, $1.29 for a quart of oil every month is cheap insurance on a $2800.00 engine.
captbone posted 03-25-2003 01:23 AM ET (US)     Profile for captbone  Send Email to captbone     
I have heard alot of BIG engines making oil, like 1271's after thousands of hours and the type but I am interested to hear that this is a problem with the smaller 4 strokes. I am surprised there is not a sensor to pick up that. I guess that is another reason for the DFI 2 strokes (not trolling). Also in a week in the dead of summer, I will get over 30 hours on my motors.
FISHNFF posted 03-25-2003 02:24 AM ET (US)     Profile for FISHNFF  Send Email to FISHNFF     
Hello jimh,
I guess you talked to the guys at OMS. I personally know of a gut with twin 90's (2001's) on a 22 Outrage with this problem, and another with twin 75's (2000's) on a 1970 21 Outrage. Both were take care of under warranty. All were under 2 years old, but had close to 1000 hours on them, so Merc must know they have a problem. If I recall right, they said it was water in the oil crankcase, not gasoline. The transoms of those two boats do sit low in the water, and they both do mostly slow trolling or drifting. I've only got a few hundred hours on my 90, and mine seems to burn a little oil, not gain. I do get blue smoke at start-up of after sitting on the water for a while. Dealer said this is normal.


PFSQUAN posted 03-25-2003 08:48 AM ET (US)     Profile for PFSQUAN  Send Email to PFSQUAN     
Capt. Bone: your reference to hearing about a 1271 making oil is interesting. I used to run a boat with Detroit Diesel 6V92 TAs, which are turbocharged engines. I had a leak in the rear seal of the engine, which caused engine oil to seep into the transmission and cause its level to rise. We could tell because a reverse gear has no combustion by products. Thus gear oil should retain its golden color unless it becomes contaminated with water, metal, etc. However, if fuel oil seeps into the engine oil, and it can if there is a leak in the metal jumper lines (internal fuel lines) a fire can occur when this mix of fuel and oil passes through the turbocharger. It happens very quickly even before you will notice a drop in oil pressure, or the oil pressure alarm sounds. This happened to me bringing the boat back from Florida one spring.

I am not sure if you are referring to a turbocharged 12V71, but in any event if fuel gets into the lube oil you have a problem.

captbone posted 03-25-2003 05:58 PM ET (US)     Profile for captbone  Send Email to captbone     
I am a very big diesel fan. Everything from the 471 DD, 453, 671, 871, 892, 1271 and 1671, and the 16v149. I have always tried to play with them and learn as much as I can. They are all great engines. If you get an old running take out, you can get them for pennies. The old turbos are the funniest looking things. They are as big as a 90hp outboard, and to get it to fit right you must co2 one part to freeze it, and heat the flange it attaches to for a good fit. I have had an old 671 run away on me because the sleeves loosened up and fuel got into the oil, when I tried to slow down the engine ran away because it drew the oil/diesel up from the crank and started to burn it. It went from 2100 to pegging the tach at 4000. THe boat runs at top 18 knots and that day I got it to 27kt. I pulled the shutdown and nothing. I then went onto the deck and used a co2 fire extingish in the air intake to kill it. I thought it was going to blow sky high it was SO loud. Another time I hit a stump at idle and got the 871 to run backward.
PMUCCIOLO posted 03-26-2003 01:09 AM ET (US)     Profile for PMUCCIOLO    
You've inspired my confidence in Detroit Diesel.


captbone posted 03-26-2003 02:24 PM ET (US)     Profile for captbone  Send Email to captbone     
Those engine where well past their life span, they are all older than me, and had a good 6000-10000 hours on them. So they just get rebuilt and still run. They are wonders. I look at the new yanmar and laugh. It is a pretty motor but that is not why you run Detriots. Also the new John deere are amazing. They are the only engines beside DD that I would use for commercial use.
Dr T posted 04-01-2003 03:29 PM ET (US)     Profile for Dr T  Send Email to Dr T     
When I was in Alaska fishing last summer, the guide mentioned having this problem in the 40 hp. Yamahas that were used in drift fishing. He said they solved the problem by changing the thermostats.
Sal DiMercurio posted 04-28-2003 08:01 PM ET (US)     Profile for Sal DiMercurio  Send Email to Sal DiMercurio     
Jim, i'd appreciate it if you could steer me in the direction you found this info, as my buddy could use some backup with other cases.
jimh posted 04-30-2003 06:23 PM ET (US)     Profile for jimh  Send Email to jimh     

The current thread here contains more info than the one I first read.

David Jenkins posted 05-16-2003 03:02 PM ET (US)     Profile for David Jenkins  Send Email to David Jenkins     
If you were concerned about your 4-stroke making oil, what weight oil would you use? I did not get a manual with my engine, but the mechanic who installed it said to use Castrol 20-50. Does that sound right?
bluerunner posted 08-23-2003 11:37 AM ET (US)     Profile for bluerunner  Send Email to bluerunner     
Jim, the following links are recent discussions about Yamaha 4 stroke F115 “making Oil”.


Clark Roberts posted 08-24-2003 07:34 AM ET (US)     Profile for Clark Roberts  Send Email to Clark Roberts     
Jenkins, the correct viscosity is important to performance and life of engine and suggest you contact manufacturor... 20W-50W sounds too heavy (thick) to me but what do I know!? Mercury recommends HD 10W-30W for my 115 EFI 4 stroker. Happy Whalin'... Clark.. Spruce Creek Navy
jws posted 08-24-2003 02:02 PM ET (US)     Profile for jws  Send Email to jws     
I have had personal experience with the "making oil" scenario. Yes, oil flowing fight up the dipstick. 50 HP Honda which I bought brand new, exactly followed breakin procedures, use the specified oils and lubricants and I always over maintain the engine. I rarely ever make "short runs". Typical run was as I made yesterday of close to 15 miles one way without stops at 4000rpm and average speed of 17.5 MPH clocked with GPS. I have installed two new thermostats not due to "oil making" situation but simply as precautionary maintenance for an engine in salt water. I also have never, ever failed to feshwater flush the engine the very same day it was used.

The engine made oil when it was shortly out of warranty. The local dealer which I bought it from claimed to be totally ignorant of the issue. I pulled the intake manifold with all three carbs and checked everything. Engine still making oil. Next I replaced the fuel pump. $80 or so. Problem solved. Earlier this year on another forum I ran across a discussion on making oil. Poster had same engine with same problem as mine with same cure.

I advise oil analysis if you have a 4 stroke and have concerns.

I also own a Detroit 4-53 powered boat. Tough little motor that will make you go deaf if you don't have great sound proofing. Fun to work on, simple, dependable, cheap to run and for parts. "Runaway" stories are some of the best.

jws posted 08-24-2003 02:10 PM ET (US)     Profile for jws  Send Email to jws     
Capt Bone. I also love those Detroits. Interesting about 2 strokes running backwards. Mercury actually made an outboard that was "fully reversing". To go into reverse the engine actually ran backwards! I have a friend who was "into" dirt bikes. He was trying out a big single cylinder 2 stroke. Unknown to him it kicked back on starting and was running backwards. He revved it and took off, going backwards! Quite a surpise.

My apology to the moderator. Perhaps a new thread on two strokes running in reverse is in order.

mrpike17 posted 05-02-2005 09:31 PM ET (US)     Profile for mrpike17  Send Email to mrpike17     
I have a 2003 Yamaha F115 four stroke that has a bad habit of oil level rising after running for a while. Also heard of another 2003 Yamaha F115 doing the same thing. On my outboard, the top cylinder spark plug fouls in cold weather. The other one did the same thing. didn;t think this would happen on a four stroke that was fuel injected. Is there a cure? It gets used on shorter trips so I switched to Amsoil 4 stroke outboard synthetic oil and when I changed it, I purposely filled it 1/2 quart low from full. After running it for a full day fishing, it was at the full mark! This really does happen and my dealer says its fuel. Doesn't smell like any gas is in there.
jimh posted 05-03-2005 01:38 AM ET (US)     Profile for jimh  Send Email to jimh     
[This two-year old thread was revived to append a comment.]

If you have a question about four-stroke engines "making oil", please begin a new discussion. Thanks.

[Thread closed.]

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