Merc 5.7 loses oil pressure, one manifold hot, white stuff on remote oil filter.

[jamanati]

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.

[jamanati]

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.

[Kevlar7r]

Pictures would help.

First thing I would do is change the oil, and see if symptoms persist.

[jamanati]

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.

[mmwjr]

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.

[jamanati]

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.

[speedysprocket]

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.

[mmwjr]

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.

[speedysprocket]

Oil should be good till well over 200.


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[mmwjr]

Originally Posted by speedysprocket

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.

[speedysprocket]

20 minutes is not long enough for oil to cool down that much.
I'd say put a bottle of seafoam in to see if loosens anything up before you resort to pulling it.


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[jamanati]

Will look to pull a valve cover off this weekend. I peek into the oil filler hole doesn't show any building.

The left manifold where the oil filter bracket is bolted was definitely hotter than the right side manifold, 160 compared to 150. The bracket was hot, so was the oil filter. Even with that, still not sure what the white stuff is on the outside.

Will probably pull manifolds and riser as well, but the white stuff has me perplexed, never seen anything like this.

[jamanati]

A peek into the oil filler hole doesn't show any build-up on either side.

[speedysprocket]

Does the pressure gradually decrease or drop suddenly?


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[jamanati]

Pressure starts out good when cold, around 50 or 60 psi. Driving after a while it still stays high 50 psi and up, then around 20-30 minutes, it starts to slowly lose pressure. From the time it starts losing pressure it will take about 5-10 minutes (at 3200 rpm) to come down to 5 psi or less, then the alarm goes off, at which I turn off the engine.

[mmwjr]

How many hours are on the engine? What you just described sounds a lot like how my old engine was at the beginning of this season but a 5 psi it was knocking up a storm. IMO a rebuild or new engine is in the near future.

[Kevlar7r]

Agree with mike. I just replaced an engine with same symptoms. It was a damaged rod bearing.

What is above that oil filter? Could rain water be dripping on it and drying/leaving a crust?

Could you have a pinhole leak in a cooling water line spraying seawater up there?

[jamanati]

Spent some time, figured some things out.
The white crust is salt. I had a circulation pump failing that was spraying water all over the place. Okay, that's fixed.
Drained oil and filter. Put in new oil and filter and 1 qt motor flush. Ran engine as per directions. Drained oil and filter again. Added new oil filter.

It's been 5 years since I did manifolds and risers, so did that. Add to that plugs, cap, rotors. Degreased and painted engine in rusty areas, plus the remote oil filter holder. Removed hoses and carb to make it a bit easier to paint.

Installed new oil pressure sender.

Pullet valve covers off, all is clean, no issues there.

Started engine, oil pressure reads 55-60 psi. Okay, been here before.

Idled for a while, pressure remained at 55-60. If I rev it to 2k or 3k rpm, pressure increases to 65-70. Been here before as well.

Took it out of for a ride, not even at 3k rpm for 5 minutes I decided to take a peak into the bilge. I dropped down to idle. Not even 10 seconds, pressure gauge went to 0. The low oil pressure switch went off sounding the alarm. Turned the engine off and checked the bilge.

No leaks, inside valve covers check out fine. But argh, seems that my carb float is now stuck open, carb was flooded and had to go back on one engine.

Okay, time to hook up a mechanical gauge and tee it inline. Now I have to solve the stuck carb float problem as well.

I managed to find this kit https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1 seems fine and priced okay. Added a few 1/8 NPT fittings to have both the mechanical and electrical gauge connected.

I guess I'm headed back to the marina again. But football and beer for today is what's on the menu.

[mmwjr]

Since gauge and alarm are going off not sure what a mechanical gauge will provide that you do not already know.

Too much fuel can get past the rings and thin out the oil but not to the point of zero pressure.

I still think that once the engine warms up the clearances increase enough that she cannot hold pressure. See if you can move the balancer around next time she looses pressure, this will be due to play in the bearings.

[jamanati]

I'm grasping at straws with the mechanical gauge maybe a wiring short in the harness at best. If the mechanical gauge also drops then it's engine pull out time.

One thing, when pressure is 0 there is no knocking or noise or any kind, runs quiet as normal.

I will see if I can move the balance next time as well.