I have a '62 340hp, which is suppose to have a sealed oil filler cap. Well, with it on the car, I consume oil at a noticeable rate, however it appears that with a vented or no cap on, I do not seem to use oil. I have had new valve seals installed and the engine was just rebiult for a second time. Internal all appears correct. I have checked the road draft tube and do not find any oil coming out of that area, nor due I have any leaks. Can anyone give me any other things to look into? I can get by with the vented cap, but the engine was not designed that way, so it tells me something is not correct. I would like to fix before, it damages anyting internally.
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Re: Oil Usage and Sealed Oil Filler Cap
Dennis, I remember distinctly this question coming up when I was pit crewing for a '60 SCCA race Corvette in the early '60's. Engine did the same thing, ate oil with a solid breather (which was standard issue) and did not consume near as much oil with a vented breather. In prepairing for the 6 hour race at Marlboro, MD we couldn't decide which one to use. Due to the length of the race, we knew we would have to add oil at a pit stop if we used a non-vented cap. I can't remember what we did. It was common knowledge to drill a 1/4" hole on the breather tube a little ways up from the lower end. The hole was supposed to help something (ain't memories great!) I think I put one on my '56 (certainly no SCCA racer car). I might be able to give you a measurement. Personally I'd go with a vented cap and when judged, put the non-vented cap on. -
Re: Oil Usage and Sealed Oil Filler Cap
Dennis, I remember distinctly this question coming up when I was pit crewing for a '60 SCCA race Corvette in the early '60's. Engine did the same thing, ate oil with a solid breather (which was standard issue) and did not consume near as much oil with a vented breather. In prepairing for the 6 hour race at Marlboro, MD we couldn't decide which one to use. Due to the length of the race, we knew we would have to add oil at a pit stop if we used a non-vented cap. I can't remember what we did. It was common knowledge to drill a 1/4" hole on the breather tube a little ways up from the lower end. The hole was supposed to help something (ain't memories great!) I think I put one on my '56 (certainly no SCCA racer car). I might be able to give you a measurement. Personally I'd go with a vented cap and when judged, put the non-vented cap on.Comment
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Re: Oil Usage and Sealed Oil Filler Cap
Is the breather installed beneath the intake manifold that leads to the road draft tube?Comment
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Re: Oil Usage and Sealed Oil Filler Cap
Is the breather installed beneath the intake manifold that leads to the road draft tube?Comment
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Re: Oil Usage and Sealed Oil Filler Cap
Paul, yes the canister under the intake is installed, in fact I replaced it during the last rebuild. Jim, thanks for the input, I know about the memory problem and I was planning to use the vented and show with the non-vented. My only concern is what is wrong? Was this a design problem? Has others experienced this or are all of the 340hp engines in Corvettes that are trailered? I sure do not want to damage the engine, but want to be able to drive it.Comment
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Re: Oil Usage and Sealed Oil Filler Cap
Paul, yes the canister under the intake is installed, in fact I replaced it during the last rebuild. Jim, thanks for the input, I know about the memory problem and I was planning to use the vented and show with the non-vented. My only concern is what is wrong? Was this a design problem? Has others experienced this or are all of the 340hp engines in Corvettes that are trailered? I sure do not want to damage the engine, but want to be able to drive it.Comment
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Re: Oil Usage and Sealed Oil Filler Cap
I agree with Jim - having spent a fair amount of my career in engine design and development, it's academic that a crankcase vent system needs both an intake and an exhaust in order to be effective; there are lots of ways to do that, but on our early Corvette engines, there is NO air intake for the vent system when using the sealed cap that the judges want to see. On my '57 270, I use the vented cap all the time except when the car is shown (Jim, this is why the 1/4" hole was recommended near the base of the filler tube for "severe service" applications). The breather canister in our lifter valley is actually a sort of (crude) air/oil separator and airflow regulator (more like a fixed orifice restriction) for the road draft tube, whose end shape and position generates negative pressure inside the tube. On more recent engines, the PCV valve acts as both a check valve and flow regulator, and the engine eats its own crankcase fumes via manifold vacuum.Comment
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Re: Oil Usage and Sealed Oil Filler Cap
I agree with Jim - having spent a fair amount of my career in engine design and development, it's academic that a crankcase vent system needs both an intake and an exhaust in order to be effective; there are lots of ways to do that, but on our early Corvette engines, there is NO air intake for the vent system when using the sealed cap that the judges want to see. On my '57 270, I use the vented cap all the time except when the car is shown (Jim, this is why the 1/4" hole was recommended near the base of the filler tube for "severe service" applications). The breather canister in our lifter valley is actually a sort of (crude) air/oil separator and airflow regulator (more like a fixed orifice restriction) for the road draft tube, whose end shape and position generates negative pressure inside the tube. On more recent engines, the PCV valve acts as both a check valve and flow regulator, and the engine eats its own crankcase fumes via manifold vacuum.Comment
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