Edmunds Answers



  • zaken1 12/11/11 9:24 pm PST

    Dipsticks usually have a flange or seal at the top that mates with the dipstick tube and keeps debris out and oil in. If this part has been damaged or the dipstick was replaced with the wrong model; it could cause a leak at that point.

    Another thing that can cause oil to come out of the dipstick tube is if too much oil was put in the engine. If the crankcase is overfilled; it will throw oil out, and is also likely to create leaks at other points. This is why it is important to only check the oil when the vehicle is on level ground (checking the oil when the car is tilted can cause the stick to read a quart or more low; when the engine really is full). A false low reading can also happen if the oil is checked as soon as the engine is shut off. It is recommended to wait at least three or more minutes after stopping the motor before checking the oil; in order to allow time for the oil in the upper parts of the engine to drain back into the crankcase.
    The PCV valve may be clean; but if it doesn't block the flow of air when trying to blow through it in the opposite direction; it will cause fuel dilution and oil leakage. Some brands of PCV valves will leak blow back even when they are new.
    If the PCV hose is plugged; cleaning or replacing the PCV valve will still not vent the engine. It is a good test to remove the PCV valve from the valve cover while the motor is idling, leaving the hose connected, and press a thumb against the end of the valve to check for vacuum. The motor should run significantly differently when you plug the valve at idle. If you don't feel suction at the end of the valve; or plugging the end of the valve doesn't change the idle quality; there is probably blockage in the hose or manifold flange.
    If the piston rings are worn, or a piston skirt is broken, or the cylinder walls are scored; this can allow pressure from the cylinders to blow by the pistons and pressurize the crankcase. That will create oil leakage which cannot be controlled. If you remove the PCV valve from the valve cover while the motor is idling; and smoke puffs noticeably from the opening in the valve cover; this is a sign of excessive crankcase pressure. An engine overhaul or replacement is usually necessary in this situation.
    The air that flows out from the motor through the PCV valve enters the motor through a hose from the air cleaner to the oil filler cap. If this hose, or the oil filler cap has been plugged or modified; it can disrupt the engine ventilation, and cause all sorts of weird problems.


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