Sheen on water exiting drive.

[Strongbad]

98 Merc 3.0 Alpha I, Engine SN 0L044623, Drive SN 0L178476

This is my second season with the boat and this is the first boat I've owned.

Noticed a few weeks ago when running the engine on the muffs in the driveway an oil sheen was on the water collecting where it ran into the grass. I stuck a bucket under the water exiting the boat and sure enough there was a visible sheen on the water. I knew the gimbal bearing needed to be changed so when the drive was off in the spring I replaced everything serviceable that is behind the outdirve with new Merc parts (shift cable, bellows, water hose, drive oil hose, shift shaft bushings, etc. I also dropped the lower unit and replaced the impeller.

Here is what I've done to try and diagnose where the oil is coming from. I drained the outdrive and pressure tested, held 14psi for over 24 hours. Went ahead and dropped the lower unit anyway and there was no evidence of oil where it shouldn't be. Just for the fun of it I replaced the shift shaft seals in the lower unit and the upper drive shaft seals under the impeller. The drive still help 14psi for over 24 hours. I also pulled the thermostat and you could see the sheen on the water under the thermostat.

The next thing I did was bypass the power steering cooler and there was still a sheen on the water exiting the boat. There is no water in the oil that I can tell from the dipstick. I'm out of ideas on where to go next. I have uploaded pics of the sheen thats clearly visible. .

I appreciate any help provided.

 

[tpenfield]

Nice diagnostic work . . .

The couple of possibilities remaining that I can think of are:

- Slight head gasket leak, but not enough to show evidence in crankcase oil. A cooling system pressure test may reveal something here

- Water getting into the cylinders, either via the intake manifold or via the exhaust manifold. Check the spark plugs after a bit of idling on the muffs for any signs of wetness.

 

[superbenk]

Prop shaft seal might be leaking a little. Maybe some fishing line wrapped around it cutting the seal?

 

[Strongbad]

Just so happen I pulled the plugs last night after alot of idle time on the muffs. There wasn't any evidence of water but the plugs do look like it might be running a little rich. Cylinders 1 & 4 specifically. I took pictures and will try and upload them. Any chance the engine is running too rich and that is fuel?

 

[stonyloam]

OK you have to look at the amount of oil you are talking about here, you will have a sheen with a layer of oil between 0.3 and 3.0 microns thick, (1 micron = ~ 0.00004 inches) floating on the water so to see a sheen on the driveway one DROP of oil would probably cover the entire driveway. Just a tiny amount of oil leaking through your valve seals, or past one of the seals in the outdrive could cause what you are seeing. With results you have seen with your testing, I would not worry about it.

 

[bruceb58]

A rich running engine will also make that sheen. Unburnt fuel will put a sheen on the water.

Let then engine completely warm up, make sure the choke is completely open, run it at a fast idle and see if you still have a sheen.

 

[Strongbad]

A rich running engine will also make that sheen. Unburnt fuel will put a sheen on the water.

Let then engine completely warm up, make sure the choke is completely open, run it at a fast idle and see if you still have a sheen.

Just tried this out. There is definitely a difference in the amount or sheen on the water when running on a fast idle as opposed to just a regular idle.

 

[bruceb58]

It's going to take awhile for all the unburnt fuel to leave your exhaust system.

If you have ever filled your tank on the water and spilled a little gas into the water, the sheen you see is the same as what oil will look like.

I don't think you have an issue. I have seen the same sheen in my driveway with different boats.

 

[stonyloam]

Yeah just a little puff of smoke from worn valve guides or rich running cold engine would do it.

 

[Watermann]

You said you pulled the t stat cover off and could see the sheen on the water under the t stat so the sheen is inside the motor's cooling system. Not sure how a rich running carb would cause that to happen?

I would run a cylinder compression check next.

 

[Strongbad]

You said you pulled the t stat cover off and could see the sheen on the water under the t stat so the sheen is inside the motor's cooling system. Not sure how a rich running carb would cause that to happen?

I would run a cylinder compression check next.

I plan too.

 

[Strongbad]

No Title

I think for the age it runs pretty well. It is 17 years old so things are going to start happening. I don't plan to keep it past this season anyway just want to enjoy it this summer and step up to something newer next.

This is how the plugs are burning. The darkest ones are cylinders 1 & 4

 

[bruceb58]

If you think oil is getting into the water jacket, a compression test isn't going to tell you much. You would be better off pressurizing your cooling system.

I still don't think you need to worry about it.

 

[Watermann]

If you think oil is getting into the water jacket, a compression test isn't going to tell you much. You would be better off pressurizing your cooling system.

I still don't think you need to worry about it.

True, guess he may be chasing a ghost, could even be the motor with aged gaskets leaching a small amount of oil where the cooling passages are but not letting water out to contaminate the oil. Most motors with some age allow a little oil to escape on the outside, I would imagine the same happens on the inside.

 

[tpenfield]

OK, how about the muffler bearings leaking oil. . . . :noidea:

 

[Watermann]

Could be blinker fluid too but boats don't have blinkers or mufflers?