Quote:
Originally Posted by PC/SR
The crankcase is pressurized by cylinder blowby, no matter the condition of the rings, there is some blow-by. Putting the end of the drain tube in the oil isolates the tube from the blow-by pressure. It is at the atmospheric pressure at the rear of the bearing that is open to the air. If there were enough crankcase pressure, oil could be forced up the tube, but I have never heard of that. The amount of pressure needed to raise the oil up and out through the tube could be calculated.
The oil in the bearing can be and is pressurized from the crankcase to some extent, but that pressure has to overcome the resistance of clinging to the bearing, and moves slowly. Also, when oil in the bearing migrates rearward to the open area and galley at the rear of the bearing, where it is collected, it is at atmospheric pressure and drains down the tube by gravity. There is not much oil that gets back there if the bearing is assembled property and the galley area is able to collect it and direct it to the tube, into the pan.
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PC, you don't have to push the oil up and out the tube, all you have to have happen is for the oil in the tube to stop flowing. Once the flow is stopped by the crankcase pressure caused by the up and down movement of the pistons, the oil returning through the rear main oil tube will overwhelm the slinger trough and run out the rear into the flywheel housing and out the cotter pin hole. I have personally had a tube fall off in my car and the leak was major and embarrassing to say the least. I have also rebuilt several engines with modified tubes that were too short that leaked quite badly.
Randall and George are right, especially George and his assessment of the pump's role in this. If you don't think the tube length matters, just cut one off 1" short and get ready to carry a gallon of oil with you on even short runs.