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Discussion Starter · #1 · (Edited)
I've got a major oil leak that seems to only happen at higher rpms for a sustained period of time. the primary source is somewhere round the dipstick. It's a fresh 383 and doesn't show any major signs of blow-by and runs great so I'm assuming that the rings seated. It also seems to be somewhat intermittent...

but we're talking losing a couple of quarts in an hour...

The engine holds good oil pressure a little over 60 psi, and I'm running rotella t in it still for break in. I do still get a little oil from the breather tubes I rounted into the air cleaner to see if it was too much crankcase pressure pushing oil out, but it didn't seem to make any difference and there's only a small amount of oil coming out there. I understand that it is not unheard of to get a little bit of blow-by on a new engine for a while as the rings are wearing in, but surely not enough to fill the bilge with oil????

It's an oversized pan and I'm assuming (almost certain) a good but standard volume oil pump.

I was thinking perhaps some may be coming from the fuel pump gasket, but surely not this kind of flow...

Any thoughts would be appreciated...

I tried to get my daughter to have a ride in the engine compartment while I ran it out for a while this afternoon, but she wouldn't go for it... damn kids these days...
 

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Someone else here mentioned their fuel pump a few days/week ago. If the diaphram goes it will pull oil out and pump it thru a vent hole...Could be worth looking into. A co-worker with a big OLD cruiser had same this spring. New pump...All better
 

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Yes, I was the one with the fuel pump. as soon as we took it out and handed it over oil came out both peep holes but it would not do it at idle or on the hose for that matter .mine leaked straight forward on the bulk head and also straight down the last couple of times out.But mine was maybe a quart for the 5 times out boating, not that much. Curt
 

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How many hours are on the engine? You said it was fresh, machined? New pistons/rings etc. It may have excessive blowby if you getting oil from the dipstick, Check your pcv valves are'nt pluged or breather on the valve cover. I may get better if the rings arent seated in fully yet. A couple boats ago I had blowby and it was the worst when trying to pull a waterskier up on one ski with the engine under high load.
 

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Discussion Starter · #5 ·
I replaced fuel pump gaskets and am fairly sure at this point that it is coming up through the dipstick. The fuel pump is new.

engine still has maybe 10 hours on it... and pulls like a train... everything is new including pistons, rings, heads, etc...

Didn't have a pcv set-up on it, but I put pcv fittings and hose on the valve covers and routed them to the spark arrestor to see if that might help. I'm not getting a lot of oil from them.
 

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Do you have "PCV" fittings or just open breathers hooked to the hose. I just ran into this a couple of days ago. A PCV valve needs to have engine vacuum to suck up the stopper in the body. Crankcase pressure will not do it. I cut the bottom off both of mine and everything works just fine now. No more oil out the dip stick.
 

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Discussion Starter · #8 ·
I'll reseal the base of the dipstick, and try going easy on it for a while.

I just have the fittings in, no valve. There isn't any vacuum on them, and I'm wondering if the valve covers have to small of an opening or if the baffles aren't suficient...
 

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I had this problem once on a 350. Changed out intake manifold gaskets (along with intake etc) and the new gaskets didn't seal right around the exhaust crossover ports and I had major blow by, but a compression test and everything else tested fine. I didn't notice this until I removed the intake manifold to start a complete tear down... found out it was the gasket, installed one with a better fit and all was well.
 

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Oh, just wanted to add that I was losing about a quart a trip too. All into the bilge area. What a mess.

I had converted the motor over to MPFI from carb and just installed everything the kit manufacture supplied. They sent the wrong intake gasket and I didn't even think about it, installed it and went. What an ordeal...until I got it figured out.
 

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Discussion Starter · #11 ·
Good thought!

... but I'm running world products sportsman heads... would be shocked if the engine builder drilled the holes...

I think I found the main source of the problem. The breather baffles on the aftermarket valve covers looked really restrictive and in fact the gromets hit the top part of the internal baffle and bent the cheap aluminum in the baffle together more creating more restriction... I kinda opened them up, and it helped a lot yesterday. I'm going to drill another set of vents in the valve covers and see if that cures it all together. I'm also tempted to drill a whole in the bottom of the flame arrestor and run a pcv hose into it for a little vacuum, but suspect the vents will cure the problem.

I also changed the valve cover gaskets, and propped down to a lower pitch for the time being so the engine isn't under as much load.

Just with changing gaskets and opening up the current crankcase vents a little, I lost a lot less oil yesterday... and with the 25 pitch prop / 1.81 gear, I could damn near stand the boat on end if I gave it a little throttle out of the hole... (grin)

I'll add a little more vent capacity and see what happens.
 

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If you are geting any water in the oil - It could be just condensation and if it builds up in the oil. When you get on it hard the oil temps go up above the boiling point of water and the water comes back out of the oil in one mad rush - The breathers are not big enough to handle all of that pressure and it will blow oil out of the dipstick.
To see if this is what is happening just remove the dipstick and cram a rubber plug into it and then go run it hard. No oil in bilge - find out why you have so much crankcase pressure. It is either water in the oil or blowby.
 

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Okay, but if you have good cylinder compression (which I did) but the engine is still huffing out the breathers and blowing oil.... I'd look into the intake gaskets. My exhaust was pressurzing the whole crank case, and blowing it out the breathers and dip stick and gaskets etc.
 

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Discussion Starter · #14 · (Edited)
Thaks a lot for the thought / experience. Under most circumstances it would be a really good thing for me to check. sorry I wasn't clearer earlier. I don't have an exhaust crossover and the heads I'm using don't come with ports drilled for one.

1adamb said:
Okay, but if you have good cylinder compression (which I did) but the engine is still huffing out the breathers and blowing oil.... I'd look into the intake gaskets. My exhaust was pressurzing the whole crank case, and blowing it out the breathers and dip stick and gaskets etc.
 
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