Ran the boat last weekend and pulling on the trailer noticed foamy oil leaking out of 1,3,5,7 valve cover breather. Pulled dipstick and confirmed.

Trailered home and WARM compression tested engine.
Results less than 8% difference between all cylinders. All 170psi +.

Leakdown tested all cylinders COLD. Less than 15% leakage on all cylinders.

Leakage air coming from valvecover oil fill hole.

Pulled oil cooler and pressure tested @ 50psi with no leaks coming from oil cooler.

Pulled riser's off and inspected gaskets and water block off plates. No signs of leakage here and no visible water in manifold runners.

Pulled intake and inspected FPP 1206 intake gaskets. No visible signs of leakage here.

Reassembled engine with new intake gaskets, riser gaskets etc and flushed engine a few times to clean out milkshaked residue.

After the 3rd flush and running on the hose for 5mins it still appears to be milkshaking the oil.

Any ideas on where to go next? Anything I missed?

Is a cracked head or block possible without the leakdown or compression test showing??? Engine has never overheated.
150* normal water temps and 190-215* oil temps cruising.

Oil pressure is normal and engine runs and revs as normal.

385ci SBC AFR aluminum heads, 010 Block.

You mention air leakage at oil fill in valve cover, but you don't mention where you are pressurizing when you get that air leakage

Did you check the lifter galley for cracks when you had the intake off?

How about running it on the hose then pulling the exhaust to see if the leakage is one particular cylinder?

I had a small crack in a head near a valve once that only leaked when the engine was warm, I found it by pulling the exhaust after running. Leakdown showed nothing.

Air was coming from the valve cover oil fill hole when doing a standard leakdown test. Cylinder @ TDC intake stroke. Pressurizing thru spark plug hole @ 100psi. Shows standard leakage past the cold rings.

I did wipe out the lifter valley and checked for cracks. Nothing visually seen. I will try pulling the exhaust right after running it and maybe do a warm leakdown test.

Thanks for the reply.

get a radiator tester and make adpters to pressurize the block with the intake on pour some green antifreeze in the block pump it up to 20 psi if it holds theres no leak there if it wont hold pressure look for where the green trail starts.

sounds like a head gasket pushing water back into the lifter galley as will allow air to come up thru the valve covers

milk shake color oil is a sign of oil water mixing. pressure check oil cooler after cleaning it with mineral sprits. when doing the leak down test pull a water hose off and listen for air or if air is coming out of the valve cover hole.

but he ran it 5minutes thats plenty of time to mix, said he allready tested cooler.

I wouldn't bother checking the cooler, if your water pressure is higher than your oil pressure you have bigger problems than milky oil a spent cooler will have oil leaving the exhaust, once enough oil exits the exhaust the pressure drops and then ( and olmy then ) will water start to replace the space that oil once was

I agree.

Sure it's not condensation right? this time of year that will happen where I will get a milky look on dipstick but the actual oil is clean and normal, I know its a stupid suggestion but you never know..

Head bolts seeping past threads?
cracked head
intake to head not seated properly or milled wrong if the heads are milled can cause it...
no corrosion under intake that would allow it to enter valley?

just a few oddball things to look at...