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Old 08-30-2004, 07:53 AM   #1
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blue smoke at startup... oil drane holes blocked??

I've read that when there's blue smoke at startup it's either bad valveseals or valveguides or then it could be clogged oil drain holes. My brother who's a mechanic told me that if there's carbon sludge blocking the holes you would probably know by checking through the oil refill hole if it is clean inside.... did that and it looked clean.
But I'm wondering if they still could be blocked??? I mean I didn't really see the holes. Where are they locatad exactly? A pic with the valve cover off would help

Thanx in advance!
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Old 08-30-2004, 09:12 AM   #2
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Sorry, I don't have a picture.

At each end of the cylinder heads there are holes to allow oil to drain back to the oil pan. One hole at each end, so there are a total of four.

In addition, there are other ways for the oil to drain back. There are other holes and slots - like where the pushrods go through the head - that also can contribute to oil drain back.

The holes vary in size depending on the particular head but generally are about the size of a nickel or a quarter.

The oil the gets pumped up the pushrods to oil the rockers and cool the springs then drains toward the front and rear of the heads, then down through those coin sized holes, into the lifter valley (where the lifters) are and then through more holes until it returns to the oil pan.

Unless your engine has very, very high mileage and received ****-poor maintenance, I seriously doubt the drain back holes are blocked. You'd have to REALLY neglect oil change intervals to cause enough crud to build up to block the drain back holes.

Blue smoke at start up is most often caused by bad/worn valve stem seals.

Jake

Last edited by JakeJr; 08-30-2004 at 09:15 AM.
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Old 08-30-2004, 11:14 AM   #3
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Click the image to open in full size.

Vortec drain back holes.

But as stated, usually a smokey startup is bad valve stem seals.
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Old 08-30-2004, 01:56 PM   #4
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The MAIN drainback holes for a SBC cylinder head are down in the depressions on either end of the head under the valve cover. If the drainback holes were plugged you might have an oil-puff-on-startup problem, however, worn out valve guide seals are far more likely. Might want to plan on replacing the seals and then just clean out the drain-back holes while you've got it apart, if they need it. That way you've got it covered from both directions.
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Old 09-01-2004, 11:14 AM   #5
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Yeah, you're probably right. The engine has been average or well maintained, so I'm sure it's valveseals.

Thanx alot guys!!!!
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Old 09-01-2004, 11:14 AM
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