Sheen in water

Jeff Fabiani said:
I ran the engine for a bit and put an oil mat on the sheen for a few minutes. I have attached that photo here. this must be engine oil, I take it by the color? View attachment 96680
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Hard to tell, but looks black, so yes possibly engine oil. I would start pulling the oil cooler and pressure testing it. Might have a pinhole leak.
 
The engine is also producing quite a bit of exhaust as well. Could the sheen just be an exhaust residue? Is that a thing?
 
Have you taken it for a good run and checked your WOT rpm? A slight miss is not always easy to detect at idle with a v8. When was the last time you threw a set of plugs, wires, cap and rotor at it? That could easily be unburnt fuel you are seeing.
 
Thornton69 said:
Have you taken it for a good run and checked your WOT rpm? A slight miss is not always easy to detect at idle with a v8. When was the last time you threw a set of plugs, wires, cap and rotor at it? That could easily be unburnt fuel you are seeing.
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I have not gone WOT recently. As of a few weeks ago I replaced all plugs and cap and rotor and that did not help. I have not replaced the wires. Would unburnt fuel look like the photo i attached of the oil pad?
 
It sounds from your first post that your engine is efi? I have seen similar sheen and even soot on the water of carbureted engines with faulty chokes. A rich mixture can cause a similar sheen. Not sure if that is possible without throwing a code with efi? Am sure a misfire could. Just throwing out ideas.
 
Thornton69 said:
It sounds from your first post that your engine is efi? I have seen similar sheen and even soot on the water of carbureted engines with faulty chokes. A rich mixture can cause a similar sheen. Not sure if that is possible without throwing a code with efi? Am sure a misfire could. Just throwing out ideas.
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Yes, the engine is EFI.

The mechanic recently looked at the engine, ran the diagnostic with no errors and said it didn't appear to be running rich. He said this engines (Merc 5.7 EFI in a 2002 DA) EFI "doesn't regulate itself between hot and cold" so at start up it's somewhat normal to be smokey and could leave a sheen. However the sheen doesn't go away after the engine is wanted up or after being ran hard.

I'm admittedly a mechanic noob and don't know all the ins and outs of a misfire. I'd assume the mechanic wouldn't be though.
 
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Jeff, i had a similar issue with my twin 5.0 efi. Shean on water and unburnt gas smell at start up. I replaced the 2 water temp sensors in the thermostat housing. These tell the computer to make fuel rich when cold and thin out when temp is right. Easy swap out and cheap start. Just remember you should have 2 on thermostat housing. 1 is to ecm and 1 goes to temp guage
 
Jeff Delbuono said:
Jeff, i had a similar issue with my twin 5.0 efi. Shean on water and unburnt gas smell at start up. I replaced the 2 water temp sensors in the thermostat housing. These tell the computer to make fuel rich when cold and thin out when temp is right. Easy swap out and cheap start. Just remember you should have 2 on thermostat housing. 1 is to ecm and 1 goes to temp guage
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Thanks for the tip, Jeff. However I have already replaced both of those sensors in the fall. I did it because my temp gauge was reading hotter than the IR reading of the thermostat housing. I replaced both sensors while I was at it. While it did fix my gauge reading, it didn't help the sheen or fuel smell.
 
I recently had a hydraulic hose for the power tilt and trim with a minor leak that left a sheen like that when I docked and I didn't have to have used the trim switch either. The tiniest drop of oil on water looks much worse than it really is. Just be sure to rule this out before spending big money as the flex hoses are prone to leaking and it's an easy and inexpensive thing to check and repair/replace. While i believe you should have either Merc trim fluid or atf in the reservoir, I have heard of some using motor oil. Again, just check to rule this out completely. Good luck!
 
Rohan said:
I recently had a hydraulic hose for the power tilt and trim with a minor leak that left a sheen like that when I docked and I didn't have to have used the trim switch either. The tiniest drop of oil on water looks much worse than it really is. Just be sure to rule this out before spending big money as the flex hoses are prone to leaking and it's an easy and inexpensive thing to check and repair/replace. While i believe you should have either Merc trim fluid or atf in the reservoir, I have heard of some using motor oil. Again, just check to rule this out completely. Good luck!
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Thank you for the tip. I did check my reservoir for this fluid and it is not low that i could see. Question for you, were you seeing the sheen without the engine running? Or only when the engine was running? In my case, there is no sheen without the engine running.
 
Jeff Fabiani said:
Yes, the engine is EFI.

The mechanic recently looked at the engine, ran the diagnostic with no errors and said it didn't appear to be running rich. He said this engines (Merc 5.7 EFI in a 2002 DA) EFI "doesn't regulate itself between hot and cold" so at start up it's somewhat normal to be smokey and could leave a sheen. However the sheen doesn't go away after the engine is wanted up or after being ran hard.

I'm admittedly a mechanic noob and don't know all the ins and outs of a misfire. I'd assume the mechanic wouldn't be though.
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Find another mechanic, no it's not normal for efi to be smoky at startup. Does the motor use oil? If your leaving oil behind it will show eventually as being low in 1 of the systems. If it's fuel you will smell it. What do the spark plugs look like?
 
scoflaw said:
Find another mechanic, no it's not normal for efi to be smoky at startup. Does the motor use oil? If your leaving oil behind it will show eventually as being low in 1 of the systems. If it's fuel you will smell it. What do the spark plugs look like?
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I have attached a couple photos of the plugs when i replaced them. These plugs in the photos were used for about 10 months.

PXL_20201022_174217184.jpg PXL_20201022_175905800.jpg PXL_20201022_180324213.jpg
 
scoflaw said:
The middle one is burning oil. First one is rnning rich and the last one looks normal.

Have you done a compression test or leakdown ?
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I have not. I did my own tune up to save money on that but looks like i should have the mechanic look at the plugs and investigate further
 
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