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I have an 88 yamaha 150 on a 20ft outrage and it seems to be leaking oil and im unsure on how to find the problem. It looks maybe like its blowing out from somewhere when the engine is running because it creates an oil slick in the water. when i take the cover off the motor there is a lot of oil underneath the motor????

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If it's clear oil, then you most likely have a hose or fitting that is loose for your oil connections.

If it is dirty oil, then it could be an exhaust gasket which will contain exhaust and unburned residue oil.

Of course I am just guessing here.

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four stroke or two stroke ?

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oliver,

I could be wrong but I don't think Yamaha had a 1988 150 hp in the 4 stroke series.
Only 2 stroke.

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There are no 4 strokes in 1988. The problem might be the oil draining from the oil tank to the lower carb. I am not sure if there were check valves installed in the hose during 1988. If there are inline hose check valves see if they are working. There also might be a check valve in the oil pump that is stuck open. When you tilt the engine up if these check valves don't work the oil will drain into the lower carb and then drain out after tilting the engine back down.

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It seems to be coming from the exhaust. If so is it difficult to change the gasket and is this bad??

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Is it leaking from the base of the powerhead or out of an exhuast port in the motor's leg section or through the prop? If from the base of the power head you will have to have the power head removed to replace the gasket. I am not sure how mechanically inclined you are but it is not that hard of a job if you know what you are doing. If oil is coming from an exhaust port in the leg or through the prop it is normal to have that unburned residue show up. If there is a lot then your system my be over oiling. Are you fouling out plugs regularly?

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I think that its coming out of the head because when i put my finger on the edge the opening its seems like oil. Could this be the gasket???