"250 chevy oil leak head scratcher..."

[vleasum]

Ok, have a 250 chevy in-line 6.

The motor has an oil leak at the top of engine where oil collects on intake/exhaust.

symptoms:
1. valve cover gasket does not leak. (forced a little air in the pcv valve with my hand over the oil filler and no air escapes.)
2. no oil slinging on the inside of the doghouse.
3. no oil around coupler in back of engine.
4. No pcv valve, only hose from valve cover to spark arrestor.

The only time I notice anything different about the engine is when I have it under power, the engine makes a hot smell. (hot oil smell)

So the question is, where is/could the oil be coming from if not for the valve cover gasket? I am stumped by the whole gravity thing. The oil seems to be coming out while under higher load. (not pouring out, but still coming out)

Thanks for your help.

 

[Bondo]

Re: "250 chevy oil leak head scratcher..."

When seaching for an Oil Leak on Anything,......

Induce the Oil Leak Condition,.... Running Hard in your case....
Then,.......
Look to the Highest point you see reasonably Fresh Oil.........
Where ever there's Oil present,... The Cleanest, Clearest point is the Leak......

I'm Betting your's Is in fact the Valve Cover,..... That's about the Only possible Answer.......
And,......

(forced a little air in the pcv valve with my hand over the oil filler and no air escapes.)

It Don't work that way.....................................

 

[vleasum]

Re: "250 chevy oil leak head scratcher..."

Here is what I have done so far:
changed valve cover gasket.
permatexed the same gasket when the gasket change didn't help.

Not only didn't this help, it didn't change the situation at all.

I originally thought that this was the problem too, but now I think that the problem is something else.

This motor has done this for a long time, I originally thought that it was related to a rebuild that was done years ago. (running the motor with the valve cover off)

The block is a rebuilt junkyard motor. the head came off the motor with the cracked block. (Swapped over all the parts)

Frustrating part is that the motor runs like a top.

 

[Bondo]

Re: "250 chevy oil leak head scratcher..."

Just How Much oil is it using,..??...

 

[vleasum]

Re: "250 chevy oil leak head scratcher..."

Here is what I have done so far:
changed valve cover gasket.
permatexed the same gasket when the gasket change didn't help.

Not only didn't this help, it didn't change the situation at all.

I originally thought that this was the problem too, but now I think that the problem is something else.

This motor has done this for a long time, I originally thought that it was related to a rebuild that was done years ago. (running the motor with the valve cover off)

The block is a rebuilt junkyard motor. the head came off the motor with the cracked block. (Swapped over all the parts)

Frustrating part is that the motor runs like a top.

 

[Bondo]

Re: "250 chevy oil leak head scratcher..."

Just How Much oil is it using,..??...

I think you said that once............
But,......
You Didn't answer My question......

 

[vleasum]

Re: "250 chevy oil leak head scratcher..."

about a quart for every 10-20 hrs. Most of those 10-20 hrs are at slow speed.

 

[ss313]

Re: "250 chevy oil leak head scratcher..."

I'm new to this whole boating thing so I may be way off base but that same 250 in a car running between 3000 and 4000 rpms is going to push am oil mist out of the breather. If it has a pcv system and not an open breather then look at all of the connections on the pcv system. If you don't see anything from there then you can look at the cam/pushrod cover. Those were common leakage areas in the auto form of that engine.

Scott

After rereading your post it could also be a tiny crack in the block under the valve cover. If that's what it is JB Weld will fix it.

 

[vleasum]

Re: "250 chevy oil leak head scratcher..."

No has a hose running to the flame arrestor. This is stock.


Thanks though.

 

[Bondo]

Re: "250 chevy oil leak head scratcher..."

Ayuh,.......... Maybe a Picture if possible would Help.........

The Only places Oil is present up there is in the Valve Cover,.....
Either along the bottom at the Head, or the Fill Cap, or the Vent Line.....

 

[whywhyzed]

Re: "250 chevy oil leak head scratcher..."

I'm thinking it's spewing out the breather tube to the arrester and dripping because of high blowby, or the baffle in the valve cover is having some sort of issue....or oil isn't draining back out of the head or something along those lines...

 

[vleasum]

Re: "250 chevy oil leak head scratcher..."

Ok, went and looked at it again, I have oil on above the engine!

Oil on the underside of the dog house (lined up to the leaking side of the valve cover (whole length)

also have above top of engine, in alignment with rear main seal. this area also has grease spattered on the underside of transom area.

I have oil that looks like it is streaking down the side of the engine directly under the intake/exhaust manifold??? Almost like it is running THRU the intake/exhaust manifold.

I have a steady 40 psig from the engine.

the front of the motor has some oil on it, but not to the extent of that the rear has.

Questions:
1. Is this thing being caused by oil running off the back of the engine under acceleration?
2. How do I determine if the rear main seal is bad?
3. what does an oil pan gasket leak look like?
4. what about the mysterious leak thru the exhaust manifold.
5. Could a rear main seal leak last for several years? Even though we haven't run it a whole lot?

 

[Bondo]

Re: "250 chevy oil leak head scratcher..."

Ayuh,........

It Still sounds like the Valve Cover is leaking........

 

[thunderroad]

Re: "250 chevy oil leak head scratcher..."

I'd get a case of brake clean aerosols and clean up the area really good, then watch and see where it starts leaking again. We use a non-flammable version of brake clean here at the shop all the time to find hydraulic leaks on our sprayers. Spray it on, it dissolves the grease then evaporates.

 

[Haut Medoc]

Re: "250 chevy oil leak head scratcher..."

Oil pressure sender?......​

 

[ziggy]

Re: "250 chevy oil leak head scratcher..."

The motor has an oil leak at the top of engine where oil collects on intake/exhaust.

since liquids only run down hill. i would think that it has to be oil fill cap, valve cover gasket, or real excessive blowby dripin out the fa or hose or valve cover connection.

changed valve cover gasket.
permatexed the same gasket when the gasket change didn't help.

ya might wanna try a new mercruiser gasket after ya get the glues off the valve cover and the head.......

I have a steady 40 psig from the engine.

what does this mean. i don't understand that.....

 

[vleasum]

Re: "250 chevy oil leak head scratcher..."

Update:

In a previous message I missed something.

I changed out the "stock" breather connections for a pcv valve that I knocked the valve out of, from there, i put a right angle brass fitting into the spark arrestor.

What I think has happened is that I have created back pressure in the engine that has resulted in the engine venting off the pressure through the past of least resistance.

Does this sound plausible?

I am going to fix this tonight.

I won't get a chance to run this until later in the week.

 

[vleasum]

Re: "250 chevy oil leak head scratcher..."

Update:
As I replaced the exhaust manifold in my boat, I think I discovered the source of the oil leak that had been "kickin' my *** for sometime."

I wanted to run this by you folks and see it it was possible that the oil leak was coming from this locatiion. Please see attached Picture.(Not my motor, but I drew the arrow in the Approximate location of a threaded plug on the cylinder head.

This plug seems to be the source of the oil.

Is this possible?

How tough will the plug be to remove?

Fun ain't it?

-V

 

[vleasum]

Re: "250 chevy oil leak head scratcher..."

Thanks for the prompt response.

I guess I should have been more specific, I wanted to verify that the plug in the head is actually a plug that COULD leak oil.

I believe I saw (for the first time) the location from where the oil was leaking. The Osco manifolds fit a little differently....

Just as an FYI the valve covers on the mercruisers I6 is actually aluminum.(nice stuff.) I don't see the oil leaking from that area.

Thanks again everybody.

 

[Fishermark]

Re: "250 chevy oil leak head scratcher..."

That picture is from the engine I rebuilt from my dad's boat. Here's another picture with the manifold out of the way:

The only threaded plug that I can remember is for the temp sender. The other plugs in that particular head are for smog fittings, which are obviously not used, so they are plugged up - but they go into the intake system, not the oil gallery.