Oil tank leak at fill cap

[pinellas50]

96 Mariner 115. I have a leaking oil fill cap on the tank under cowl and can't figure out why.

The tank has been on the motor for a year and a half with no issues. I filled it on Saturday before heading off to the ramp. The motor was up in the trailoring position. When I got to the ramp I found the tank was dumping oil during the trip.

I have inspected the tank, cap, and o-ring on the cap. Everything looks fine. I can tighten the cap down but everytime I raise the motor up to trailoring position oil starts coming right past the o-ring on the fill cap. I have tried taking it off and putting it back on several times to see if it will seal but it doesn't. There are no cracks in the tank or the cap. The o-ring is free of imperfection and still pliable.

Has anyone else run across this and found a fix. I don't mind buying a new cap and/or o-ring but I hate wasting money if this isn't the fix.

I can't believe something this simple is getting the better of me!

 

[j_martin]

Re: Oil tank leak at fill cap

Look closer. They crack if you overtighten them.

 

[pinellas50]

Re: Oil tank leak at fill cap

The tank you mean? That was my first thought too. As in a crack in the fill neck of the tank, the fill neck expands when you tighten the cap and the O-ring is pushed out from the cap, and then oil gets by.

I was back at it last night for at least a half hour with a high powered flash light trying to find any type of crack no matter how small. Nothing. The oil comes past the O-ring but there is no leak from the filler neck under the O-ring which I would expect if there was indeed a crack.

I know the ultimate answer is to replace the whole thing..tank, cap, and all. But that wasn't all that cheap the first time and I would like to avoid it again. Is this my only real option here?

 

[j_martin]

Re: Oil tank leak at fill cap

No, I mean the cap.

Is this a new thing, or did you inherit it with the engine.

Maybe wrong parts (O-ring)

 

[pinellas50]

Re: Oil tank leak at fill cap

Oh. Well a cap is only $30. That doesn't hurt near as bad and is a much easier job than the tank swap.

This is a new problem. I have never had a problem with it until Saturday. I took the cap off to add oil and then put it back on as usual. I found the problem after my short trip to the boat ramp right after that oil fill.

I looked the cap over last night too and nothing caught my eye. But I honestly invested most of my time looking at the tank. I'll inspect the cap more closely tonight.

Thanks for your continued help j_martin!


EDIT: And now it has stopped leaking! I did absolutely nothing to it and it stopped. Great, another intermitent problem to look forward to.

 

[wingnut4041]

Re: Oil tank leak at fill cap

Check and see if the cap on the air vent is in place,it is a black cap about as big around as a quarter,on top of the oiltank halfway between the front and back,if it's missing you may be missing the duckbill valve under it causing the oil to leak out {and run off the oil cap} when the engine is tipped all the way up.

 

[pinellas50]

Re: Oil tank leak at fill cap

The vent baffle thing is there. The mechanic that just did the lync and sync on the motor just put a new one on actually. That was one of the first things I checked because it was new and I didn't install it. But that was a good idea, thanks.

I could clearly see the oil level rise, in relation to the fill cap, as I tilted the motor up. Then I could see the oil start coming past the O-ring.

So far it still hasn't leaked. I had it out on the lake for a test and tune last Saturday and then brought it home. So.......I don't know.