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TOPIC: Crank case breather hose leaking oil

Crank case breather hose leaking oil 11 Aug 2017 03:29 #1

  • Landin
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Hello all,

Got a strange issue and had a couple questions... recently on a long boating trip I came across an oil leak... I traced it back to the port side crank case breather hose at the connect point on the valve cover...the leak appears to be between the hose end going into the cover and the gromit. I played around with it, moved it around, cleaned it and it just kept leaking... the amount of oil was very minimal... but I just can't figure out why it happening...engine has less than 40 hrs on it....

I have been troubleshooting my oil pressure gauge for a while and believe it's fixed... but has not been 100% confirmed....

Couple questions -

Anyone think my oil pressure is too high and causing the leak? I'm using the correct oil viscosity.

Perhaps I should just buy a new breather hose and see if that solves it?

I inspected the starboard side and really noticed it was a much more of a tight seal than the port side.

Thanks for any input! Cheers!

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BOAT: 1991 - Bayliner 2556 Ciera Flybridge
ENGINE: 357 Alpha 4V (275HP)
OUTDRIVE: Alpha Gen 1
RATIO: 1.47:1
PROP: 15 1/2" X 15"
NAME: "Knotty Oar"

Marine Search and Rescue Crew - rcmsar.com/rescue-stations/southern-region/north-vancouver/

Crank case breather hose leaking oil 11 Aug 2017 04:30 #2

  • builderdude
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Landin, if the valve covers were clear you'd be amazed at the amount of oil being spit from the pushrod/rocker arm area. I think you've just got a loose grommet and the hot oil is weeping through. ;)
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Dave
Edmonds, WA
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Crank case breather hose leaking oil 11 Aug 2017 04:33 #3

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Oil pressure looks a bit higher than mine but my engine has many hundreds of hours on it and yours is new. What does the gauge read at idle after a long hard run at say 3500 rpm? What oil are you using?
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Dave
Edmonds, WA
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.030 over-Vortec top end-part closed cooled
***The rebuild of my 2556***
www.baylinerownersclub.org/index.php/for...ansom-repair-my-2556

Crank case breather hose leaking oil 11 Aug 2017 12:40 #4

  • Landin
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Hi Dave...(as always, thanks for your input) I'm heading out for a weekend trip later today and will confirm the RPM vs. Oil pressure.

Another strange thing I noticed was my cruising speed... at approx 2800 - 3000 rpms I'm getting about 10 nm/hr... does that speed seem incredibly slow to you? I'm running a 357 with a brand new leg... 1 month ago, I painted the hull and cleaned the prop and leg and slapped on a fresh coat of paint on the out drive... I keep reading our boays r heavy... but does that speed not seem very low to you?

Cheers!

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BOAT: 1991 - Bayliner 2556 Ciera Flybridge
ENGINE: 357 Alpha 4V (275HP)
OUTDRIVE: Alpha Gen 1
RATIO: 1.47:1
PROP: 15 1/2" X 15"
NAME: "Knotty Oar"

Marine Search and Rescue Crew - rcmsar.com/rescue-stations/southern-region/north-vancouver/

Crank case breather hose leaking oil 11 Aug 2017 14:57 #5

  • tdcooper99
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builderdude wrote: Landin, if the valve covers were clear you'd be amazed at the amount of oil being spit from the pushrod/rocker arm area. I think you've just got a loose grommet and the hot oil is weeping through. ;)


So glad someone posted about this, as it's been annoying me for a while. I've got the exact same issue... leaking out oil from that port side breather hose connection. Is this grommet a replacable part or is it a new valve cover?

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Tyson, Ackerley, Sidney & Gene
Tsawwassen, BC
1996 2858 Ciera Command Bridge
Mercruiser 7.4L BRAVO II (GEN. V) GM 454 V-8; Engine Serial 0F603347
"Island Passport"
Home marina: Point Roberts, WA

Crank case breather hose leaking oil 11 Aug 2017 15:37 #6

  • Centerline2
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the grommets are easily replaceable, but may have to be ordered. any autoparts store will have them or can get them and the grommets are usually ordered by size rather than engine model....
you should check the plastic insert that the blow-by hose connects to to see if its cracked. clean it and inspect it very closely as I have seen these crack and leak.

engine oil pressure has nothing to do with a leak at this spot, as there is no pressure to it, but the oil is only being splashed up there by the moving valves..

and 10kts at 3000 is slow... something is wrong. mine was only making about 10kts @3100, and after checking and testing everything I could, I removed the exhaust and found a faulty flapper seal. it was restricting the flow to the point the engine couldnt breath right. it ran absolutely fantastic, but wouldnt develop any power as the rpm increased....

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1989 Bayliner 2556, 5.7 OMC Cobra

Crank case breather hose leaking oil 11 Aug 2017 16:07 #7

  • Jim Gandee
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Landin, the area within the valve cover is somewhat pressurized from the crankcase (piston ring blow by). Some of that oil that is being thrown about the valve train, as well as the oil in the case, is atomized and exits that area via the breather tube you describe. This process is normal, and in fact the crankcase pressure must be relieved or other, bigger problems will result. The oil leak you describe is most likely a result of a poor seal between the valve cover grommet and the tube but it can be exacerbated by a restricted breather tube. Thus I'd verify there is no blockage of the tube, within the tube or at its terminas, which is usually at/near the air filter.

Regarding the oil pressure- I seriously doubt that is an issue at all. Most engines will operate perfectly fine from 10-80 psi. If you are concerned about high oil pressure first thing I'd do is verify the accuracy of your OEM gauge and sending system by temporarily installing a direct pressure gauge.

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Crank case breather hose leaking oil 11 Aug 2017 16:57 #8

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The problem can also be as simple as an old rubber grommet that is dried out and brittle. They don't seal when they get old.

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1988 Capri Cuddy 1950 OMC 5.7

Crank case breather hose leaking oil 11 Aug 2017 18:49 #9

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T in a manual gauge and leave it there.

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Be good, be happy, for tomorrow is promised to no man !

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Crank case breather hose leaking oil 14 Aug 2017 01:14 #10

  • builderdude
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Landin wrote: Hi Dave...(as always, thanks for your input) I'm heading out for a weekend trip later today and will confirm the RPM vs. Oil pressure.

Another strange thing I noticed was my cruising speed... at approx 2800 - 3000 rpms I'm getting about 10 nm/hr... does that speed seem incredibly slow to you? I'm running a 357 with a brand new leg... 1 month ago, I painted the hull and cleaned the prop and leg and slapped on a fresh coat of paint on the out drive... I keep reading our boays r heavy... but does that speed not seem very low to you?
Cheers!


Sorry for the late reply, was out for a weekend boat trip to hood canal area.
Cruising at anything under 3000-3300 RPM is most likely burdening the engine pretty good, I'm running at 3300-3600 RPM Doing 22-27 MPH (SOG- via GPS)
What's your drive ratio?
EDIT: I see you have the Alpha 1.47:1......not sure where it should be in relation to my Bravo 2:1 but think you should be cruising at 20 MPH minimum.
I think Your oil pressure is good, where's it at when idling?

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Dave
Edmonds, WA
"THE FIX"
'93 Ciera 2556 Mercruiser 5.7 Bravo II
.030 over-Vortec top end-part closed cooled
***The rebuild of my 2556***
www.baylinerownersclub.org/index.php/for...ansom-repair-my-2556
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