Rusty oil

[muskrat808]

Hi - When doing my end of season oil change on 1972 4 cyl Mercruiser oil was brown, rusty colored, I assume water is in it . So -blown head gasket ? cracked block ? . What should be myfirst diagnostic move ? Thanks

 

[Bondo]

Hi - When doing my end of season oil change on 1972 4 cyl Mercruiser oil was brown, rusty colored, I assume water is in it . So -blown head gasket ? cracked block ? . What should be myfirst diagnostic move ? Thanks

Ayuh,..... Sounds like plain ole dirty oil,....

Water will cause a milkshake of poo,....

 

[sean.deangelis]

Well, some details are needed. Does the boat have closed cooling? If "yes" you'll need to pressure check. If "no" a compression check is probably the fastest diag to narrow the possibilities.
Anything silly last season like the engine dieseling when you shut it down? Specifically when hot?

 

[fishrdan]

Google "milky oil" and you will see what water in oil looks like, milkshake like Bondo said. When I think of "rust" colored oil, that sounds normal to me.

 

[muskrat808]

Thanks for the replies . I think it's more than just dirty oil , the last 3 or so changes didn't look like this . Also there was a milkshakey appearance inside the valve cocer / oil filler area . It is an open cooling system so I think a compression check is in order . Later

 

[Fishermark]

A bad riser / elbow or manifold is a more likely cause than bad compression (cracked head or something similar). (That's if you find you really do have water in your oil).

 

[Bondo]

Thanks for the replies . I think it's more than just dirty oil , the last 3 or so changes didn't look like this . Also there was a milkshakey appearance inside the valve cocer / oil filler area . It is an open cooling system so I think a compression check is in order . Later

Ayuh,.... That much of it is Condensation,..... The valve cover is where it happens,......

Usually, a good hard run clears it right up,....
Gotta get the motor, 'n oil up to temp, to steam off the Condensation,....

It's never a bad idea to do a compression test,.....
But, if ya got water in the oil, it won't tell ya,....

A coolin' system pressure test, Will,...

 

[Watermann]

If you still have the used oil drained in a container see if it has water that separated.

 

[tank1949]

Have older 95 proline 295 and it's the worst motor hatch design in history of boating. I had to jury rig cab cover since rain and sea spray would overcome hatch and drip rigt into carb throat down flame arrestor bolt. Found Milky water in crank after a week of rain a couple years back. I change oil and made jury rig modifications and haven't had rain intrusion since. If you have a place or hatch similar, you might be experiencing similar results. Sea water cooled maniforld last about 4-6 years if stored wet in salt h2o. Imagine what your motor looks like inside?????? Alway good to examine side of manifolds and inspect for external leaking after every flush with fresh H2O.

 

[muskrat808]

Thanks again for more replies . I don't think there are any rain water intrusion issues and it's in fresh water .I considered the milkshake to be condensation and hope it is but won't be checking on that until the spring . The oil is gone so can't check for water . Hopefully it is an elbow/manifold issue and not the block ( assuming I have an actual issue ) .Need to dig up a compression tester . Later

 

[muskrat808]

Ok- checked the compression , good news- all 4 cylinders same compression , maybe bad news -all at around 58 psi . However - gauge was loaner from auto parts store and engine is winterized and therefore tested cold . Did quick check on 94 Honda with no known engine issues with same gauge and also got 58 psi . So would testing with engine cold yield such a low reading ( last tested warm 3 yrs ago - all around 140 psi ) or is it the gauge out of calibration ? Any thoughts ? Thanks

 

[fishrdan]

Did quick check on 94 Honda with no known engine issues with same gauge and also got 58 psi .

Sounds like a bum gauge to me, take it back and get another loaner. Or, just buy one, not terribly expensive.

How many revolutions were you turning the engine over on each cylinder, were all the spark plugs removed, battery 100% charged and throttle wide open?

 

[muskrat808]

Fishrdan - Yes I agree about the gauge . Plugs were all removed , battery charged up and did enough revolutions for the gauge reading to stabilize ( 5-6 ) .Did not check the throttle opening however . Thanks

 

[muskrat808]

OK , finally got a new compression gauge . Now readings are 140 + for cylinders 1 ,3 ,and 4 but 120 + for number 2 . When squirt oil into # 2 reading is almost 150 . So ring wear in # 2 ? Should I take off exhaust elbow and check that for possible water in oil source or run it awhile with muffs to see if there really is a water intrusion ? I don't think elbow or the rubber exhaust hose have ever been inspected or replaced . Should the rubber be replaced as preventive maintenance or let sleeping dogs lie ? It looks externally to be in good shape . Thanks

 

[Watermann]

Not sure your going to get water intrusion into the oil from the exhaust manifold side. Water in oil is more of a head/intake gasket or cracked block issue.

 

[Alumarine]

Can you provide a picture of the oil in a clear container?

 

[Fishermark]

Not sure your going to get water intrusion into the oil from the exhaust manifold side. Water in oil is more of a head/intake gasket or cracked block issue.

From personal experience I can assure you it is possible to get water in the oil from the manifold / exhaust side. :blue:

 

[Bondo]

From personal experience I can assure you it is possible to get water in the oil from the manifold / exhaust side. :blue:

Ayuh,.... But only after shut-down,.... The water still has to get past the rings,......

I'm not at All against checkin' the exhaust manifold, 'n more importantly, the gasket surfaces 'tween the manifold, 'n riser,.....

I'm still thinkin' the rusty oil came from condensation rustin' the upper motor, under the valve cover,...

 

[Fishermark]

I don't disagree with the idea of it being condensation. But... the boat is a 1972 and the poster says he believes the elbow, etc has never been touched. That's a long time - even in fresh water! (In the water here in SW Florida there would be nothing left but a pile of rust!)

 

[muskrat808]

Thanks for the additional input . It's been unusually warm this winter in Oregon so I'm going to get the engine out of winterized mode soon . Will running the engine out of the water with muffs be sufficient to test the condensation theory ? If so , how long should the running time be ? Thanks