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Old 05-27-2019, 09:14 PM   #1
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Default Mercruiser oil question

1998
2800 scr
7.4 mercruiser bravo 3

I have an oil leak and think it’s coming from the hose that comes out of the valve cover and goes into the flame arrestor on carb.
Appears to be leaking around the grommet where the hose fitting is on the Valve cover.
I was expecting this to be a PVC but it’s just an open plastic elbow fitting. Seems like a tight fit but I’ll replace the grommet
My question is:
I was reading that this type of leak can be caused by increased pressure caused by bad piston rings.
Certainly hope that’s not the case.
Boat runs great. No issues. The leak started mid season of last year and isn’t severe but definitely leaking.
Curious if anyone else had a similar problem.
The oil baffle appears to be in place in the valve cover under the fitting.
Thanks
Mark
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Old 05-27-2019, 11:56 PM   #2
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I typically see a small amount of oil film here by the end of the season. If its a lot than you most likely have a higher amount of blow by due to worn rings. I would perform a compression test which is never a bad thing to know the condition of your engine.
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Old 05-28-2019, 11:02 PM   #3
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What is your oil pressure reading? I doubt that worn piston rings will increase oil pressure, if anything you would see lower oil pressure.
Usual causes of high oil pressure is faulty relief valve or incorrect oil viscosity.
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Old 05-28-2019, 11:39 PM   #4
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Quote:
Originally Posted by jrsick View Post
What is your oil pressure reading? I doubt that worn piston rings will increase oil pressure, if anything you would see lower oil pressure.
Usual causes of high oil pressure is faulty relief valve or incorrect oil viscosity.
Not saying worn rings increase oil pressure but the blow by increase pressure in the oil pan, this pressure is relieved through the breather and the higher pressure blows out oil.

Rings have no impact on the oil system pressure.
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Old 05-29-2019, 01:56 AM   #5
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So I bought the boat in 2014.
Survey did compression test at that time.
One cylinder was a bit lower but not anything terrible. Mechanic said prob carbon around valve and suggested
Additive to add to gas which I did.
Boat now has 700 or so hours on it. Maintained and not abused. Almost never over 4,000 rpm.
Cruises 3,200 rpm.
Oil pressure good at 60 psi or so but i understand that worn rings and cause pressure in oil pan which isn’t actually oil pressure
Runs great no problems.
I’m going to tape a rag around the fitting to verify that it’s leaking there.
Thanks for all the info I’ll report back with what I can find out.
Thanks!!
Mark
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Old 06-04-2019, 03:34 AM   #6
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Im most cases leaking oil at the pcv valve on a small block Chevy (from what Ive seen) is caused by the rubber grommet it goes into getting hard and the oil flying around in the valve cover leaking out. If it is truly blow by pressure it will be more common from worn valve guides/seals (top end of the engine) and should be present at where the tube terminates at the spark arrestor also, a compression test is never a bad idea in these cases.


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