An engine must have the breather flowing... DON'T block the breather! Your engine needs to breath surprisingly enough, as it heats up the oil expands, oil vapours form and pressure will build up in the engine. If the engine is not able to breath expect the pressure build up to start forcing the oil out of the engine. It will flow out of any hole, I have seen a 6n polo pissing oil out the dipstick and this was a "lucky scenario", the oil could further damage seals and rings, followed by a starvation of oil to the engine...
You get the picture I'm sure.
