Effects of engine oil overfill.. help?

HI.. i have a 1994 Toyota Corolla that i have had for a quite a few years. I keep everything in great order on it. a few months ago it started makin a strange noise and i had all the belts and all the hoses replaced under the hood. Friday i took it to get the oil changed. after i picked it up i drove i straight home (which was about 5 mi. from the shop) the next day when i cranked it up it started makin a knocking noise in the engine. It was sitting on a level surface so i pulled the dipstick out and checked the oil level. it was really overfilled. The shop swears they didnt overfill it and that it wouldnt hurt anything.. but I spoke to some of my friends who say that overfilling with oil can cause a great deal of damage. can anyone tell me what those damages might be? if anyone could helpi would greatly appreciate it.

Overfilling the oil in an engine can cause several issues -- a litle bit overfilled, and the crank will start splashing in the oil -- this robs power, and will "whip" the oil in the engine like in a blender -- this will cause air to get in the oil and decrease its effectiveness. Alot overfilled and the oil will create severe pressure resistance inside the crankcase such that the seals in the engine (oil pan, front and rear main, valve cover, and even the head gasket) will begin to leak oil and eventually fail, resulting in a costly repair.

Correct the overfill ASAP by letting oil out until the level is correct. Engine oil is checked when the engine is NOT running -- If you check it while the engine is running it will likely read high -- Make sure you remove the dipstick and wipe it clean before re-inserting it to check the level against the stick "marks."

* The Corolla 1.6L only uses 3 quarts of oil, even with a filter -- 4 quarts is too much.

wal mart constantly over fills.i gave up and bought ramps and do it myself now.