I have a '57 with solid lifters. It uses alot of oil and the mchanic says that part of it is blowby. The oil pressure runs about 60#. I have been told that the problem might be reduced with a vented oil cap. Does anyon have any thoughts on that and if I changed to a vented instead of the correct non-vented cap, approx. how much judging deduction would there be? Thanks
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Re: Engine blowby and oil cap
you need to run a leak down check to see the condition of the rings and then check to see what type of valve seals are on the engine. if it still has the "O" ring and steel cup type i would try changing to the umbrella type to stop the oil burning. -
Re: Engine blowby and oil cap
you need to run a leak down check to see the condition of the rings and then check to see what type of valve seals are on the engine. if it still has the "O" ring and steel cup type i would try changing to the umbrella type to stop the oil burning.Comment
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Re: Engine blowby and oil cap
Rex -
The "correct" non-vented cap was released for solid-lifter engines due to "oil pull-over" problems on cars used for racing, where high-rpm crankcase pressure tended to blow oil vapors out of the vented fill cap as well as out of the road draft tube. The hydraulic-lifter engines used the vented cap, which is the "intake" point for crankcase ventilation, with the road draft tube as the "exhaust" when the car is in motion. This crude system is only effective when the car is moving and a low-pressure area is created at the bottom of the road draft tube to draw vapors out of the crankcase; when the car is sitting still with the engine running, vapors will exit at both the road draft tube AND the oil fill cap, as there is no "suction" at the end of the road draft tube.
I have both caps - the "correct" sealed cap for judging, and the vented "breathing" cap for normal driving; I've put 5,000 miles on my '57 270 since I restored it four years ago (with the vented cap), and have no signs whatsoever of any oil vapors on top of the engine.
Make sure your road draft tube isn't plugged or restricted; also, there is an oil separator "can" at the rear of the lifter valley under the intake manifold whose function is to baffle any liquid oil from exiting through the road draft tube; if the innards of that can are sludged up, the only exit point for crankcase vapors is through the oil filler cap. If your engine hasn't been rebuilt in a long time, you may have a lot of blow-by pressure in the crankcase, which will defeat the function of the ventilation system.Comment
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Re: Engine blowby and oil cap
Rex -
The "correct" non-vented cap was released for solid-lifter engines due to "oil pull-over" problems on cars used for racing, where high-rpm crankcase pressure tended to blow oil vapors out of the vented fill cap as well as out of the road draft tube. The hydraulic-lifter engines used the vented cap, which is the "intake" point for crankcase ventilation, with the road draft tube as the "exhaust" when the car is in motion. This crude system is only effective when the car is moving and a low-pressure area is created at the bottom of the road draft tube to draw vapors out of the crankcase; when the car is sitting still with the engine running, vapors will exit at both the road draft tube AND the oil fill cap, as there is no "suction" at the end of the road draft tube.
I have both caps - the "correct" sealed cap for judging, and the vented "breathing" cap for normal driving; I've put 5,000 miles on my '57 270 since I restored it four years ago (with the vented cap), and have no signs whatsoever of any oil vapors on top of the engine.
Make sure your road draft tube isn't plugged or restricted; also, there is an oil separator "can" at the rear of the lifter valley under the intake manifold whose function is to baffle any liquid oil from exiting through the road draft tube; if the innards of that can are sludged up, the only exit point for crankcase vapors is through the oil filler cap. If your engine hasn't been rebuilt in a long time, you may have a lot of blow-by pressure in the crankcase, which will defeat the function of the ventilation system.Comment
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Re: Engine blowby and oil cap
I have a simular problem in that my 1960 dual quad engine blows a fair amount of oil through the vented cap. This motor was rebuilt 500 miles ago. In place of the road draft tube, I have copied the 61 pcv setup. I have a very good draw through there and my oil seperator can is clean and in place. I suspect that maybe my rings have not fully seated, but I doubt these engines did this brand new off the showroom floor. Would I be able to keep a cleaner top of my engine with the road draft tube in place?Comment
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Re: Engine blowby and oil cap
I have a simular problem in that my 1960 dual quad engine blows a fair amount of oil through the vented cap. This motor was rebuilt 500 miles ago. In place of the road draft tube, I have copied the 61 pcv setup. I have a very good draw through there and my oil seperator can is clean and in place. I suspect that maybe my rings have not fully seated, but I doubt these engines did this brand new off the showroom floor. Would I be able to keep a cleaner top of my engine with the road draft tube in place?Comment
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Re: Engine blowby and oil cap
Sean -
I'd think that your RPO 242-type setup would be more effective, as it draws all the time, whether the car is moving or not, as long as the PCV valve is working. Essentially the same system (except drawing from a valve cover after the rear block vent went away) was used for many, many subsequent model years.Comment
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Re: Engine blowby and oil cap
Sean -
I'd think that your RPO 242-type setup would be more effective, as it draws all the time, whether the car is moving or not, as long as the PCV valve is working. Essentially the same system (except drawing from a valve cover after the rear block vent went away) was used for many, many subsequent model years.Comment
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Re: Engine blowby and oil cap
I have a solid lifter '60 and at hi rpm was blowing oil. My motor was just tired. An engine is a big pump, and when that pressure leaks from the valves or pistons its got to go somewhere, ie out the breather or the road draft tube. I rebuilt the engine and am running a non-vented cap now with no more problem. (knock wood)Comment
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Re: Engine blowby and oil cap
I have a solid lifter '60 and at hi rpm was blowing oil. My motor was just tired. An engine is a big pump, and when that pressure leaks from the valves or pistons its got to go somewhere, ie out the breather or the road draft tube. I rebuilt the engine and am running a non-vented cap now with no more problem. (knock wood)Comment
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