What Is Wrong When My Oil Level Fluctuates With the Gas Pedal?
Your car's engine represents a confluence of several technologies and systems, with each affecting another in some way. Although your car's air and fuel systems make it go, the hydraulic oiling system is what keeps it going. Oil level fluctuations don't necessarily mean anything serious, but under certain circumstances such fluctuations can be a harbinger of impending failure.
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Oiling System Basics
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Almost all engines use a wet-sump, gravity-return oiling system. A wet-sump system uses an oil pump to suck lubricant out of a sump, or reservoir, at the bottom of the engine. The pump pressurizes the oil and sends it through the engine's oil galleries, or channels, so that it can travel to the bearings and valvetrain. Much of the oil eventually works its way up to the top of the engine, where it drains back to the sump through a series of holes and channels.
Normal Fluctuation
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A certain amount of oil level fluctuation is normal; the amount varies by engine size, type and cylinder count. Almost all production engines use hydraulic lifters or cam adjusters that contain a plunger or cylinder. As engine rpm rises, the oil pressure increases and the lifters fill up with oil to push the valves open further. While individual lifter/adjuster displacement is fairly small -- typically about 1/2 oz. per lifter -- the engine uses at least two of them per cylinder. As such, the lifters on a typical V-8 engine can pull an extra 8 oz. of oil out of the sump at high rpm.
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Drainback Problems
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If the engine's oil drain-back packages become clogged with sludge, oil will get trapped in the top of the engine and fail to return to the sump. Depending on the size of the passages and the severity of the clogging, the oil might take a few extra seconds to return to the sump or it may not return at all. Slow oil flow is a precursor to complete drainback failure, which is a very bad thing for your engine. Inline engines are somewhat more prone to this type of failure than V-configured engines, which tend to have more and larger drainback holes.
Treatment
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A complete system flush is the only way to eliminate the sludge clogging your drainback holes. It generally takes at least 1/4 inch to 1/2 inch of sludge build-up to clog drainback holes to the point that they affect the oil level, so you'll probably need to run a very powerful oil-flushing solvent through the system multiple times before the problem goes away. Pour some oil-flushing solvent into your engine, then drive it as you normally would for about 20 miles. Drain the oil and change the filter, then replace the oil with cheap 0W-20 weight motor oil and more solvent. Allow the car to sit at a fast idle to about 20 minute, but do not drive it. Drain the oil; repeat this flushing/refilling procedure with 0W-20 oil and solvent until the oil no longer looks like black syrup while draining. Once the oil comes out clean, replace it with a high-mileage synthetic oil and new filter. Here's a tip: to set your car at a fast idle, slide two or three nickels between the throttle bracket on your carb/throttle body and the throttle-stoop plate or adjusting screw.
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