Is it a new boat to you? If not, Has it never happened before? Have you made any changes?

Olds are known to do this if run a to high of an rpm for too long. Oil drain back is their downfall. They pump oil into the heads and it is slow to drain back if run too hard.




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OK. So like I said, it’s THE problem with Olds boat motors. Even with 2 breathers, it will still probably happen ( I have a breather in both valve covers and it still does it). One thing that has helped is that I run 8 quarts of oil even though I have a 10 qt pan. But if I stay in it too long it’ll start to blow.
Excessive crankcase pressure could also be an issue. Boat motors should have a little more clearance between the piston and cylinder. Excessive blow by might be an issue and with the constant high rpm, trying to push that pressure out along with the build up of oil= a big mess.
It’s been argued here wether a PCV helps a boat motor or not. I personally don’t think so.
A puke tank can be added. Or if you had over the transom headers, a crankcase evacuation system.
There was a guy that went by Bunger that added external drain back lines to his Olds that helped the puking problem. I’ll see if I can find the thread.
The added breather can help a little. But it will also be another place to puke oil from if you push it too hard.
What most have said over the years, cruise an Olds with only short bursts of hi RPM.
They can be a great motor but need some machine work and modifications to without these issues.
Also check out 69Kona (his name is Lee, I think). He has a hard running Olds and was build a circle race boat with an Olds as well.



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Thanks for the info..... I'm gonna try and run two breathers and see what happens....a little oil I can handle but if it's still bad I'm gonna invest in a puke tank

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i have had a lot of experience with the olds oil puking . mine use to even come out of the distributor gasket. what the issue is the olds pumps all its oil into the heads and does not drain back fast enough!! if you do some looking around on olds sites you will find where the racers have actually drilled drain lines from the back of the heads to the pan with good results.. may not be something you want to do but its probably the best way!

i personally dont think the rpm is your problem, we ran our 69 tahiti with 455 BBO for 15 years, 3 different versions of the same motor.  it would only ever just drip out of the breathers occasionally.  Maybe 10 drops after 45 minute runs averaging 3500 - 4000 rpm constant. (Avi to pirate cove or pirate cove to the sand bar.)

i personally feel you have excessive blowby or excessive oil in the heads from some other issue.

you can also pull the valve covers off and make sure there is nothing blocking the oil returns in the heads.  2 per head, front and back.

all factory iron heads are the same.  if it was sitting for a long time, possible something got in.

did you put a clothes hanger wire through them to make sure, head and block together should only be about 3" max to get through.

Also, next time it happens, pop the oil fill tube cap off and see if a bunch of air is pushing out? 

Is this the first time you have had the motor running on the water?

Have ran the boat a few times and been working out the issues. I did away with my pcv valve and am running two breathers on valve covers and I put a breather on my oil filler for added ventilation along with new valve cover gaskets..... Going to run it next weekend.....thanks again for all your input..

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