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  #1  
Old 09-22-2008, 09:53 PM
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Why Is Oil Coming Out Of The Filler Cap?

I did the blow-by test where I let the filler cap set on the engine as the engine idles, and the cap did not move at all. So apparently my engine does not have much blow-by. I've noticed, though, that it leaks oil out from the filler cap and the tube next to it. Is this normal, and if so, do I need a new cap seal, and maybe a tube leak fix?

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Old 09-22-2008, 09:59 PM
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Pretty normal for rubber going on 30yrs old.
You can get a new oil filler cap, and maybe seal up or tighten the blowby tube.
Shouldn't have that much oil coming out unless it's not on tight.
It is in fact caused by blowby, or compression in the cylinder head cover.
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Old 09-22-2008, 10:15 PM
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You can either replace the cap, replace the seal or apply bearing grease to the existing seal. Any of the three should stop the leak.

Quote:
It is in fact caused by blowby, or compression in the cylinder head cover
Incorrect. Its caused by a poor seal between the valve cover and oil cap.
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Old 09-22-2008, 10:57 PM
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The easiest oil leak. Some filler caps are interchangeable with gas caps... if you're very cheap.
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Old 09-22-2008, 11:03 PM
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I replace the oil cap seal at every oil change, no need to replace the whole cap.

The breather hose was around $15.00 the last time I bought one, and it's an updated part that eliminates the two part elbow and hose they used to use.
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Old 09-22-2008, 11:24 PM
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agreed. I had an OEL cap from an older diesel that I swapped with the upgraded platic version and had the same issue. Went back to the plastic with a better seal, no issues
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Old 09-22-2008, 11:40 PM
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Thanks for the responses.
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Old 09-23-2008, 12:48 AM
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Quote:
Originally Posted by ForcedInduction View Post
Incorrect. Its caused by a poor seal between the valve cover and oil cap.
I agree wholeheartedly with you here, but isn't the root cause of the oil blowin around in there blowby?
I know when I've seen serious blowby, it gets dirtier much more quickly once the cap's off-
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Old 09-23-2008, 01:24 AM
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Quote:
Originally Posted by UriahT View Post
I agree wholeheartedly with you here, but isn't the root cause of the oil blowin around in there blowby?
I know when I've seen serious blowby, it gets dirtier much more quickly once the cap's off-

oil is sprayed around by the valve train
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Old 09-23-2008, 02:31 AM
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TB is right, take off the oil cap and look at the cam with the engine running. Each lobe has an oil jet spraying onto it so there are 10 lobes, tappets and valve springs slinging oil all over the place. The blowby gasses are flowing up from the front of the engine through the timing chain passage towards the rear of the valve cover so blowby actually blows most of the oil spray away from the oil cap. An engine with high blowby is more likely to have lots of oil in the air filter housing.
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Old 09-23-2008, 10:33 AM
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Quote:
Originally Posted by UriahT View Post
I agree wholeheartedly with you here, but isn't the root cause of the oil blowin around in there blowby?
I know when I've seen serious blowby, it gets dirtier much more quickly once the cap's off-

I'm with you on this one.

valve train def has splash effect, but all blowby shoots up through the timing chain channel in the front of the engine...right below the oil filler cap.

older ,worn out engines, are often dirtier b/c of blowby passing through numerous worn out seals
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Old 09-23-2008, 11:03 AM
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If I take the filler cap off my 240D and let it run it will shoot little droplets of oil all over the place making it look like I heated some cooking oil on the stove and threw a couple drops of water on it. I'd think that's excessive blowby but it is short almost a quart of oil . Would oil level effect this?

Take your cap off, pull the rubber seal out, clean all the oil out with a rag, put the rubber seal back in upside down so the groove is now on pointing towards the top of the cap and you have a good seal for a little while. Worked for me
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Old 09-23-2008, 11:49 AM
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Quote:
Originally Posted by Squiggle Dog View Post
I've noticed, though, that it leaks oil out from the filler cap and the tube next to it. Is this normal, and if so, do I need a new cap seal, and maybe a tube leak fix?
On mine, some moronic PO or mechanic used a screwdriver to lever on the cover through the hole, leaving a nice divit in the lip that the cap seal mates to. I doubled-up on the oil cap seal to get that leak under control, and I'm sure the "fix" won't last for long .

Mine also leaks by the breather tube. I looked at it and concluded it is just going to leak by design -- there's no way to form a completely oil-tight seal with that design, although you might get close by removing every last bit of film of oil on the mating surfaces before assembly.
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Old 09-23-2008, 12:19 PM
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there's no way to form a completely oil-tight seal with that design
There is, I posted it earlier. Put a layer of high-temp wheel bearing grease on the seal.
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Old 09-23-2008, 08:08 PM
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Quote:
Originally Posted by ForcedInduction View Post
There is, I posted it earlier. Put a layer of high-temp wheel bearing grease on the seal.

How long does the fix last? I think ill go do that

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