Oil Slick

[JPringle]

2006 340 twin 8.1 496’s. My boat is in the water full time. I was doing an oil change and after sucking the oil out of the port motor, I noticed an oil slick B had formed on the water. The only place where I could think of where it would have come from is the underwater BNO exhaust. Ordinarily, there never is oil in the water. The port engine had water in the oil and how that occurred is still unknown which prompted the draining. Any ideas on how I would get oil in the water?

 

[markrsimon]

Most engines (if not all) have an oil cooler where the raw water comes into the boat, through the trans cooler (if inboard) and then through the oil cooler.

If the oil cooler has a leak, that allows raw water into the oil and vise versa leading to a slick.

Pull the water hose on the oil cooler and its pretty easy to tell if thats the issue. MrCool has good replacements.

Depending on the amount of water in the oil, one of more oil changes may be required. While you can get the engine up to temp to evap the water - it could cause additional wear and tear, thus several oil changes with 5min run times may be best. Oil/filter changes are cheap compared to engine changes. Tractor supply has oil in 5 gallon jugs for good prices.

 

[Bill Curtis]

2006 340 twin 8.1 496’s. My boat is in the water full time. I was doing an oil change and after sucking the oil out of the port motor, I noticed an oil slick B had formed on the water. The only place where I could think of where it would have come from is the underwater BNO exhaust. Ordinarily, there never is oil in the water. The port engine had water in the oil and how that occurred is still unknown which prompted the draining. Any ideas on how I would get oil in the water?

How old are your exhaust manuals and risers?? Exhaust used in salt water only lasts 5-7 years typically. When they develop a leak, water gets in thru the exhaust valves, ie: water in the oil. Can also be a bad head gasket, intake manifold / gasket (if yours is a wet one) and , as stated in above post, the oil cooler.

 

[JPringle]

How old are your exhaust manuals and risers?? Exhaust used in salt water only lasts 5-7 years typically. When they develop a leak, water gets in thru the exhaust valves, ie: water in the oil. Can also be a bad head gasket, intake manifold / gasket (if yours is a wet one) and , as stated in above post, the oil cooler.

The manifolds and risers are new. I suppose I won’t know for sure until it’s all taken apart. Compression test is next.

 

[JPringle]

Most engines (if not all) have an oil cooler where the raw water comes into the boat, through the trans cooler (if inboard) and then through the oil cooler.

If the oil cooler has a leak, that allows raw water into the oil and vise versa leading to a slick.

Pull the water hose on the oil cooler and its pretty easy to tell if thats the issue. MrCool has good replacements.

Depending on the amount of water in the oil, one of more oil changes may be required. While you can get the engine up to temp to evap the water - it could cause additional wear and tear, thus several oil changes with 5min run times may be best. Oil/filter changes are cheap compared to engine changes. Tractor supply has oil in 5 gallon jugs for good prices.

Good to know. The engine is only about 2 yrs old with new manifolds and risers. I wouldn’t expect the gaskets to fail so soon. I’ll replace the oil cooler do a few oil changes and see if that clears the issue. Thanks!

 

[Flyer5]

Most engines (if not all) have an oil cooler where the raw water comes into the boat, through the trans cooler (if inboard) and then through the oil cooler.

If the oil cooler has a leak, that allows raw water into the oil and vise versa leading to a slick.

Pull the water hose on the oil cooler and its pretty easy to tell if thats the issue. MrCool has good replacements.

Depending on the amount of water in the oil, one of more oil changes may be required. While you can get the engine up to temp to evap the water - it could cause additional wear and tear, thus several oil changes with 5min run times may be best. Oil/filter changes are cheap compared to engine changes. Tractor supply has oil in 5 gallon jugs for good prices.

Just had to replace my starboard oil cooler for this reason.