"Discussion" in another group

It would have to be overfilled by a lot, but yes, overfilling can cause hydraulic lock. To cause hydraulic lock, the pan would have to be filled enough to submerge the crankshaft and fill the air space under the pistons.

How much oil? If you are meaning "hydraulic lock" not allowing piston / crankshaft / internal component movement by overfilling a bit, I don't think so. If you mean filling the entire crankcase, maybe. If you fill each individual cylinder with oil, yes. Overfilling your crankcase oil can result in a loss of fuel mileage, interruption of normal design oil flow causing lack of lubrication, foaming, excessive emissions, and probably a few more that Ray O can elaborate on. It is usually highly recommended that the crankcase oil fill level does not come into contact with the crankshaft unlike an air cooled motor that has a splash lube system that normally uses a "paddle" bolted on the bottom of the rod bearing.

I doubt if 3 quarts over in a 4 quart system is enough to cause hydraulic lock. I've seen fast lube places and DIY-ers drain the automatic transmission oil and then add 4 or 5 quarts to the crankcase without causing hydro-lock, although the transmission tends to get trashed. You get the problems from possible foaming, but the engine usually doesn't run very long after they figure out that the vehicle won't move.

BTW, draining the transmission fluid seems to be a less common mistake these days. I think it became prevalent when transverse-mounted drivetrains were introduced and people didn't know what they were looking at from underneath.

Econo lube replaced my cousin /roommates engine after they filled it twice doing a oil change. It blew a big hole in the block before she got it into 2nd gear.

Lets see. Hydraulic lock would only occur if the movement of the pistons were prevented by the lack of a compressible substance... Oil. You would pretty much have to get every drop of air out of the system. Even in the event that you did, usually one piston is moving up while the other is moving down. It would seem to me that this would relieve any pressure build up from other pistons going down. I would vote no. But I'm not a physicist... yet. :)