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Old 09-12-2016, 12:10 AM   #1
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Default Merc 5.7 loses oil pressure, one manifold hot, white stuff on remote oil filter.

Have a twin engine 5.7 L Merc.
Both engines start out fine with oil pressure, cold, and idle, 40-65 psi
After driving 20 or 30 minutes, port engine gauge starts to drop, alarm goes off. Starboard engine shows fine, still 40-60 psi.
Temperature on both engines is fine.

Of the two exhaust manifolds on the port engine, one is around 115-120 degrees, the other (port side) is around 155-160 degrees.
Starboard engine manifolds are around 115-120 as well.
Okay, so may be time to do manifolds again, its been 5 years.

The problem/question I have is regarding the remote oil filter. Same laser temperature reader shows the oil filter around 155-160 degrees on the port motor. And it has this white stuff all over it.

The oil is clean, even changed about a month ago. Dipstick level looks fine. No idea why the remote oil filter looks this way. Any ideas would be helpful. Thanks.
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Old 09-12-2016, 12:12 AM   #2
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20160911_174516.jpg

20160911_174527.jpg

One remote oil filter looks fine, clean, that's on the starboard motor, which is running fine.

The other remote oil filter is white, looks salty or crusty, engine loses oil pressure on this engine, plus port manifold runs hotter than the starboard manifold. Oil filter is also very hot to the touch.
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Old 09-12-2016, 12:13 AM   #3
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Pictures would help.

First thing I would do is change the oil, and see if symptoms persist.
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Old 09-12-2016, 12:18 AM   #4
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I had the issue about a month ago, low oil pressure.
Swapped out oil pressure sender switch, gauge, etc. Those were fine.
So I did replace the oil and filter, pressure came back. That was a month ago.
What's odd is that at idle and then even for 10-15 minutes, oil pressure is fine.
Then is starts to lose pressure, goes to zero, and alarm goes off.
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Old 09-12-2016, 02:09 AM   #5
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What does the oil pressure drop to?

Any knocking noise?

Could be the oil pump pressure regulator getting stuck open.

My 5.7 lost oil pressure when hot this year along with a knock, it was the main bearing and crank worn out. I replace the engine. The cheap fix would have been to install a crank kit but for the same work but more $'s I got a now long block.
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Old 09-12-2016, 05:25 PM   #6
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Oil pressure on the gauge drops to 0, alarm goes off right before it does.
I didn't hear any knocking noise when the alarm went off, I did shut the motor off.
When I started it again about 45 minutes later, pressure was around 20 psi.

Any idea what the white stuff may be on the remote oil filter?
It wasn't white at the beginning of the season back in May. It looked the other picture I posted.
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Old 09-12-2016, 08:29 PM   #7
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Can you pull a valve cover to just get an idea of the internal condition of the engine? Maybe you've got a severe sludge problem and as it breaks up, it's clogging passages until the pressure behind it drops and it falls out of the passage.
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Old 09-12-2016, 08:32 PM   #8
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Really not sure what it is.

Try unbolting the oil filter bracket from the exhaust to see if the hot manifold/riser are heating the oil up and thinning it out. Use some cord to tie it off so it's not laying on the engine.
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Old 09-12-2016, 10:29 PM   #9
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Oil should be good till well over 200.


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Old 09-12-2016, 11:11 PM   #10
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Quote:
Originally Posted by speedysprocket View Post
Oil should be good till well over 200.


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Yes but it does get thinner and if the engine has loosened up in the main bearing it may loose pressure, yes a long shot.

However since it goes to zero but then recovers has me thinking it's the oil pump bypass that regulates the pressure.
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