Oil slick out the back

[BoatNoobie]

Alright, I've noticed this a couple of times now. I thought it was from when I put gas in a few weeks ago, a little bit spilled into the splash well. It even discolored the polyurea a slight green color.

Maybe it still is but I find it hard to believe since gas usually evaporate pretty quickly. Maybe it's having a reaction to the polyurea and leaching something off.

Or maybe there's an oil leak in lower unit or main motor. Or maybe gas from the motor somewhere.


Example from today. I backed trailer and boat into water with the motor tilted upwards. I throw my line down the dock and start walking towards it. Along the dock, I saw just a tiny bit of sheen on the surface. Wasn't sure if I was the cause of it. When I got to the boat, that's when I saw a little bit more sheen at the rear of the boat. Tilt the motor down and it doesn't seem to be getting worse.

Got a couple hours of fishing in. I kept going to the rear deck to see if I saw any sheen while fishing but looked normal to me. I even allowed a wake to fill the splash well and see if the runoff had a sheen but it didn't.

Thought was ok until I got back to the dock. After putting trailer in water, I saw a tiny bit of sheen along rear again.

What to look for?

Vexus 1880 w/ Merc 115

[JoePA]

Isn't the fuel fill on those in the splash well? If so I'd make sure that the cap is closed but also it may be venting out that as well. Did you have a full tank of fuel?

[BoatNoobie]

Isn't the fuel fill on those in the splash well? If so I'd make sure that the cap is closed but also it may be venting out that as well. Did you have a full tank of fuel?

Yes fuel is at rear. I dont think it's leaking. The few times I've opened the cap, there would be a release of pressure. It was also relatively cold out yesterday. About high 40s only.

I also have just slightly over 1/4 tank according to the gauge. In my previous boats, I would drain all the gas when I winterize. Not sure if I can do that with the vexus easily. On the old boat, I have a nozzle fitting for where the motor connects to in the splash well for fuel. Made it very easy with a pump and hose.

[Guntucky]

May not be your boat. Ramps are notorious for having the sheen you described just because of all the boats that are using the area, and putting in your boat could have stirred up oil or fuel that was there previously.

[alli ss]

Yes fuel is at rear. I dont think it's leaking. The few times I've opened the cap, there would be a release of pressure. It was also relatively cold out yesterday. About high 40s only.

I also have just slightly over 1/4 tank according to the gauge. In my previous boats, I would drain all the gas when I winterize. Not sure if I can do that with the vexus easily. On the old boat, I have a nozzle fitting for where the motor connects to in the splash well for fuel. Made it very easy with a pump and hose.

You can find the end of the fuel line easily enough under the cowl. Unhook it there and you can use the same setup

[BoatNoobie]

Alright, took the boat out today. Backed boat into water and tied off onto the dock. Sure as hell looks like it's coming out of the motor somewhere.

Here are pictures of when I had it on the dock. The motor hasn't been started yet. It was just sitting there tied off. It dissipated after about 10 mins or so and I didn't see anymore of it.












Then I started the motor and looked out the back. And saw slick forming again. So here's a video of it.


When I get out onto the water, I do not see this at all. I'll stay in the back when it's still and nothing. Start the motor and nothing. From the video, it looks pretty obvious it's coming from the motor. I'm thinking it's coming out of the pee hole on the side. I don't think it's coming out of the prop. In the video, motor is in neutral. I wonder if it has something to do with being tilted up, then down.

[doogiecox]

Boatnoobie, I’m not sure if the 115hp motor has this issue, but I have the regular 150 four stroke and it did or at least mine had a leak on the little white cap on the power trim unit, and I noticed a oil sheen behind the motor, because every time you would trim the motor it would seep just enough to keep it wet around the little white cap plug on the power trim unit, maybe this might help you some.

[tcesni]

My motor had the same symptoms last year and my seals were blown. But that was on a 14 year old motor and yours must be nearly new.

[BoatNoobie]

My motor had the same symptoms last year and my seals were blown. But that was on a 14 year old motor and yours must be nearly new.

Which seals? Motor has 8.3 hrs on it

[BoatNoobie]

Boatnoobie, I’m not sure if the 115hp motor has this issue, but I have the regular 150 four stroke and it did or at least mine had a leak on the little white cap on the power trim unit, and I noticed a oil sheen behind the motor, because every time you would trim the motor it would seep just enough to keep it wet around the little white cap plug on the power trim unit, maybe this might help you some.

What did you do to fix it? Did the cap just need to be tighten?

[doogiecox]

BoatNoobie, my dealer ordered a new cap and O ring from mercury and replaced it, they had to unbolt the motor to get to it, the technician said it was a little loose, and they went ahead and changed it out with the new one, but nothing looked wrong with the old one, other than it felt loose and when you worked the power trim it would seep a little power trim oil, but it’s been fine every since they changed it.

[jcdogfish]

Oil level?

[Bradley Lane]

Do you have hydraulic steering? Maybe leaking. It’s happened to me before.
Good luck !

[figueira]

boatnoobie had the same issue oil was leaking from one off the compressor hoses.
do you see any oil or spots where you park your boat?

[BoatNoobie]

Oil level?

It was fine when I first got the boat. I haven't checked since but will later.

[BoatNoobie]

Do you have hydraulic steering? Maybe leaking. It’s happened to me before.
Good luck !

I imagine if that's the case, I'll see evidence of it in the splash well though.

[BoatNoobie]

boatnoobie had the same issue oil was leaking from one off the compressor hoses.
do you see any oil or spots where you park your boat?

It's parked outside in gravel/ground mix. So if it's a small drip, I'm not going to be able to tell.

Where are these compressor hoses? Inside the cowling?

[bill duffy]

Problem could be from power trim. With boat at home raise and lower motor several times . Take white paper towel and wipe around trim rods. If you find oil, trim unit is leaking and a seal would cure the problem at your dealer.

[sclark]

if you find no evidence of a oil leak anywhere, here are some other things to check .
1. this could simply be road oils, kicked up when trailering down the road, which could leave a thin film of "oily" substance on the bottom of the hull
2. Could be car / truck exhaust by products, again leaving a slight residue on the exterior hull (especial if towed by a diesel).
3. Could be coming out of the outboard exhaust as a by product of a engine that has set after being run, check the exhaust for any discoloration or carbon build up.
4. Starting a cold fuel injected engine could also cause excessive fuel to be injected and not totally burned in the start up process.

i am sure most of you know it only takes a drop of oil to leave the tall tale sign of a oil slick.

just some random monday morning thoughts on this :-)

[james_az]

check the top and bottom gear case plugs. - may also wanna check your engine oil level, make sure they didn'd overfill.