I feel liking an idiot asking this, but I don't think I've ever known the right answer: how much oil should you have in your engine (where on the dipstick should the oil be)? Do you fill it up to the full mark?

 

full mark

the bad here is that the top surface of the oil gets in the way of the engie operation and air gets into the liquid (foam). the oil w/ air does several things not as good like dissipate heat etc.

 

The oil level can be ANYWHERE between the "add" mark and the "full" mark - YUP! ANYWHERE in between. Contrary to popular belief, your engine will not explode nor will it suffer irreparable damage if you do not continuously fill it up to the "full" mark. There is no need to drive across town, check your oil and fill up that last "x" on the dipstick for fear of something horrible happening to your engine.

This is about as FALSE a statement as you can possibly see on this forum. The top layer, IF the oil level is between the "add" and "full" marks on the dipstick, will NOT in any way interfere with engine operation.
1. Our engines have an oil splash shield that controls this even if the level has been slightly overfilled.
2. You need about 1/2 qt. overfill before the crank will strike the surface of the oil in the oilpan. It is ONLY then, that you will get that portion of the oil to foam from the physical disturbance of the crank as it slams into the oil. It is this foamed oil that does not lubricate well, nor will it pump well if it should get into the oil pump.

 

Thanks xviper - extremely helpful as always!