Did you manage o check the oil? Sounds like it was very low or some coolant got into the oil and was burning off. Neither is good. Hard to say more without seeing it.

 

I checked it when the car is off. I checked the coolant level and it was minimum level. It's not good right? do you recommend me to stay away from that mini?

 

Of all the fluids in a car, only one produces steam. Water has no business being in the crank case. Walk away quickly.

 

its normal when the oil cooler gasket leaks coolant into the oil...

 

If you don't smell antifreeze in the oil or the oil is not milky then it's normal water in the engine. Burning any hydrogen carbon based fuel produces water as a byproduct. The small amount of piston blow by gases condense in a cool or cold engine. Once the engine gets to operating temp it steams off the water and is removed by the pcv system. That's why people with oil catch cans collect so much water, it comes from the fuel. So if you open the oil fill cover at the right time you will see steam coming out of any engine. My 2005 dodge has water under the oil cap all the time. Never any in the oil though. Take a look once the engine has reached operating temp for a little while, the steam will be gone. This is also one of the reasons why oil goes bad, the condensate is acidic and the additives get used up fighting this problem. So a lot of blow by? Do more frequent oil changes.

 

I didn't smell anything and oil was not milky.

 

If the engine was at operating temperature for any period of time, any residual condensation/moisture should have boiled off and been scavenged by the PCV system. Normal operating temps for these engines exceed the boiling point of water.

 

I would be more concerned with the timing chain and vacuum pump. These are the two main engine problems and will detonate one instantly when those two parts fail. Find out the maintenance history of the car and go from there. Check the oil fill cap with the engine running. If the steam is not present then the pcv system is working as it was designed. If you can't remove the cap because the vacuum is to high then the pcv system has failed. Some of these problem are more prevalent on the turbo cars.
do a Google search on how much water is produced by the burning of hydrocarbon based fuels. It is ALOT of water. I'm in Canada and all new homes have very high efficiency furnaces. Drains are installed for the a/c and the furnace condensate. Highly efficient furnaces are also called condensing furnaces. Instead of the water being sent outside with the hot exhaust more heat is extracted and it causes the water to condense. Proper drainage is required as a result of the acidic water. I know this is a little off topic but just trying to help you understand whatsm going on, have a great day!