What causes the oil to come out the dipstick?

Usually only three reasons why the engine oil will come out of the dipstick.

1 - The engine oil level is above the maximum limit set by the manufacturer

or

2 - The crankcase is being over-pressurised

2a - the cylinder pressure is escaping into the crankcase and effectively blowing it out of the dipstick tube

2b - the engine breather system is blocked or not operating as intended

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Check the engine oil level (on flat ground) and ensure the level is between the marks indicated on the dipstick.

Carry out a compression test to ensure the cylinder compressions are all at the acceptable level specified by the manufacturer.

Check the engine breather system and clean any debris or residue from within.

N.B

This problem can be caused by just one or a combination of all three possible areas so my advise is to check all of them regardless of maybe finding the oil level being too high.