How much blow-by is normal? - Ford Powerstroke Diesel Forum
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  #1  
Old 08-26-2008, 02:27 PM
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How much blow-by is normal?

Hello all again. I have a quick easy question this time. How much blow-by are you guys getting out of the oil fill cap with the engine running? A buddy was wondering how much is normal on his 7.3, because he noticed smoke out of the oil fill cap. I also get a fair amount of smoke, but if you put your hand over it, there isn't a lot of pressure blowing out. Are whiffs of smoke normal on an engine with 60k miles on it? The 7.3 has something like 250k miles on it. Thanks!
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Old 08-26-2008, 02:45 PM
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I think the test is to put the cap on the spout upside down and if it blows off you have excessive blow by. My truck smokes pretty good and i only have 91k on it. I think the 7.3's all have a fair amount of blow by.
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Old 08-26-2008, 04:30 PM
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I asked this question too, because I have a what I thought was a significant amount of blowby, but Scuffy says it's normal for my 119K mile truck. It's enough to see at a stop (I have the CCV mod). It pisses the drive through people off enough to make them close the window on me--LMAO
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Old 08-26-2008, 06:35 PM
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I will go try the test. My guess is that the cap will stay on mine, but maybe not the 7.3. I suppose blow-by is not as much of an "issue" on diesels, is that about right?
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Old 08-26-2008, 06:47 PM
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Originally Posted by dieselkane View Post
I will go try the test. My guess is that the cap will stay on mine, but maybe not the 7.3. I suppose blow-by is not as much of an "issue" on diesels, is that about right?
Blow by is normal on a diesel to an extent. You will see some when you take the cap off. But you can tell the difference between a lil bit and excessive.
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Old 08-26-2008, 08:04 PM
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So if you hold your hand over the oil fill, is it "normal" to feel pressure? Mine smokes out of it, but I cannot actually feel air blowing out. Where as some engines, (like our 1975 diesel massey tractor) have a lot of blow-by, to the point where you can hardly hold your finger over the CCV hose that comes off the valve cover.
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Old 08-27-2008, 03:35 PM
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I would say your just fine. I have seen some road tractors that the ccv dumps out under the engine and they were smoking like a steam locomotive. Like i said before, mine also smokes out the cap and like Jon said its normal for diesels to do just that.
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Old 08-27-2008, 03:54 PM
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what would cause the blow by?? my 97 has some.
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Old 05-02-2009, 02:39 PM
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Bump cause I have the same question....
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Old 05-02-2009, 07:46 PM
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excessive wear in the cylinders is the cause of blow by.
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