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Just performed my 5th or 6th oil change and I’m fighting my ocd nature. I always put in 5.7 quarts but when I check the dipstick it shows as being a little over every time by 1 or 2 mm.
Should I worry about the over fill (leaking seals, carbon on the valves…), or just let it go?
Also how much do you guys add? I’m thinking of just going with 5 quarts in the future. Requires the purchase of just one 5 quart jug, no need to buy that extra quart and pour only .7 quarts. Would make life easier, but then I worry about the benefit of missing that extra little bit to help with the life of the oil.
 

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5.7 quarts is the ideal engineered specification, but the real-world tolerance is almost certainly much wider - the crankshaft might start whipping up the oil if you put 7 quarts in it while the oil pump might suck air causing a loss of oil pressure on a steep hill or sharp turn if you put 3 quarts in it. The level of oil in the oil pan is several inches deep. A difference of 1-2 mm is inconsequential.

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Whenever I get a new car, the first oil change I fill with one quart less than the specification, start the car to circulate the oil, then check the oil level to see where it is on the dipstick. If between the marks, I drive it to warm it up, then let it set for a couple of hours to let the oil drain back to the pan. Checking at that time sets the benchmark for how much to add at each oil change which is always less than the fill specification.

After that first oil change, I know how much to bring the level back to just under the full mark on successive oil changes. I never would repeat an overfill if it happened on the first time. That is OCD...one does not repeat actions they feel are incorrect.
 

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Yeah, first oil change I was like, this only takes 5 quarts? Checked the level... right between the lines.... and it's been 5 quarts every change ever since. However... I certainly don't check at every fueling like recommended!

Kind of like the rear diff... says 1.9 but I always need that 3rd quart and add more like 2.1 for the stuff to come out the fill hole.
 

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Seals are not going to see any more oil pressure than usual. One would have to intentionally way overfill……to the point of hydro-locking under the pistons.
 

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Even that's not a concern because the crankcase volume remains the same over each engine revolution since half the pistons are moving up while half are moving down. If you grossly overfilled the engine with oil to the point that it was contacting the bottoms of the pistons, the engine it would shuttle oil between opposing cylinders while attempting to start it. Hydrolocking occurs when there in an incompressible fluid on the top of a piston and the valves close and the piston moves up.

The real concern with overfilling the oil is the aeration that occurs when the level reaches the height of the crankshaft which acts as a beater (think about beating egg whites to make meringue). Aerated oil results in a lower volume through the oil pump and doesn't lubricate or cool as well.
 

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I thought with overfilling (I don't know how much constitutes an overfill) they say that it gets into the PVC and intake. Not sure what ill effects that has. Car Care Nut referenced it's better to underfill slightly that overfill. Just did 1st oil change on the RAV, capacity 4.8, easy to eyeball.
 

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The PCV lines are near the top of engine well above the level of the pistons. In theory, you might get more oil mist being sucked into the intake if the oil level is high enough to reach the crankshaft, but the aeration of the oil is the bigger and more immediate problem.

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Depending on how drunk one is, the motor can be filled with oil way past the point aeration would occur.
 

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A quart high, and you'd have more oil than needed. A quart low, and you'd have less. Either way, proper lubrication will occur.

As @zroger73 outlined above, unless you overfill to the aeration point, it's really not big deal, because the oil will do it's in tended job.
 

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The PCV lines are near the top of engine well above the level of the pistons. In theory, you might get more oil mist being sucked into the intake if the oil level is high enough to reach the crankshaft, but the aeration of the oil is the bigger and more immediate problem.

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What would be best approach to check a PC valve, to determine if its working or needs replaced?
 
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