2002 Mercury 90hp Four Stroke Milky Oil

[Ppopps]

Just bought a used boat, thought I'd checked everything, ran it on earmuffs, gear oil was clean, but never pulled the dipstick. Got it home and notice that the oil level was WAY past full mark. Drained the oil and swear darn near 6-7L came out (should be 5 L) and the oil is super viscous and grey in colour. Wouldn't say there are streaks, but does smell potent, maybe like gas. It is not foamy, if that means anything. What should I do next, test compression?

Heard something about bad water lines that run through the sump and corrode on these motors (causing water in oil) but can't find that thread now, nor a diagram that helps me to know what to take apart and look for.

I'd guess there's gas and water in the oil, what should I do..other than cry about my new big purchase?

-Ppopps

 

[rickdb1boat]

Re: 2002 Mercury 90hp Four Stroke Milky Oil

It is a known issue for these engines to "Make oil" through fuel in the oil caused by blow-by from the rings. It comes from the engine running too cool or not being run at higher RPMs much. For more info, search google for "4-Stroke Engines Making Oil" ...

 

[Ppopps]

Re: 2002 Mercury 90hp Four Stroke Milky Oil

Thanks for the reply. Yes, I've read all about that now since I discovered this with my "new" boat, but everyone seems to say their oil stays the same colour when it happens (makes sense to me if it's only clean gas getting in) but in my case the oil looks very grey in colour....would that not suggest there's more to it than running cold?

To give more history, the previous owner says he did use it for trolling a lot at 5 mph since the last oil change...so maybe this makes some sense, but it's the colour (sorry "color" for you kind Americans, I'm a Canuck) that has me so scared. Would that not mean water? When people say "milky", does that actually mean white or with streaks? Mine is even grey.

-Ppopps

 

[Silvertip]

Re: 2002 Mercury 90hp Four Stroke Milky Oil

I agree with you that there are two issues here. If the oil smells like fuel, there is an issue with too much slow speed trolling. The engine needs to be run hard periodically to keep that problem under control. Mily engine oil is also a sign of water intrusion.

 

[Ppopps]

Re: 2002 Mercury 90hp Four Stroke Milky Oil

Thanks, so any idea what to do next? As I said in my original post, read something somewhere on this board about a common problem with water lines that run through the sump corroding on these engines (though mine has only ever seen fresh water and the motor could pass for new looks wise) but I can't find that post now.

I heard that a compression test won't tell you if you have a bad head gasket....

I don't mind taking it to a dealer (though I'm fairly competent with a wrench myself) but I don't want to just throw good money after bad and want to go about it methodically....

Thanks, Ppopps

 

[rodbolt]

Re: 2002 Mercury 90hp Four Stroke Milky Oil

run a leakdown test, not only can it detect a bad headgasket it can also detect piston rings that have rotated and the gaps have lined up.
two main reasons for making oil is running to cold and overpropped, especially on EFI 4 strokes.
myself I would inspect the T-stat for proper operation,do a leak down test then change the oil and filter and go run it, you will need at least 30 min above 4000 RPM to heat the oil.
dunno about any water tubes in the oil sump, thats a new one on me .
my F150 tends to run cold with extended trolling the block will actually cool to about 110*F and the head to about 120.
so when I am done I make sure I make a 30 min run above 4000 RPM.

 

[boatmanjf]

Re: 2002 Mercury 90hp Four Stroke Milky Oil

Local shop said there can be two issues with this.....Making oil is a common problem....If the oil sump has too much oil, The engine can blow gaskets, but more common is the oil cooler that you are suspect of already,,The bad news is you have to tear down to find it.. Change the oil and run the engine without a lot of slow speed. See if you oil goes bad agiain....Oil is cheaper than a tear down, and it will tell you if you must.