loosing coolant over a couple of days. any experience on where it's going? 150Km

Unless you have money to waste I suggest you have the cooling system pressure tested to find the leak. You need to stop driving this car until you fix the leak. The water pump is driven by the timing belt. Unless you want to blow a head gasket. Go to www.alldatadiy.com to get all the factory info you need to do this job. It will cost you $26.95 for a full year. For $26.95 you will get any info that pertains to your car. It is the same info that professional repair shops pay for.

If its not on the ground, pull the engine oil dipstick. If its milky or has water in it sorry, bad juju. Does the cab of your rig smell like coolant ( hot and musty ) or any wetness on the passenger side floor or behind the glove box/air bag. If so your looking at a heater core/line issue. As for as changing the water pump, if the rig has a mechanical fan ( driven off the motor and water pump ) pain in the butt if you dont have the right tools. If the vehicle has electric fans your ok. Just remember to drain the cooling system first.

The way an automotive shop would locate the leak is by removing the radiator cap and attaching an adapter that screws on in place of the radiator cap. Something that looks like a bicycle pump with a pressure gauge attached to it is used to "pump up" pressure to simulate pressure generated when the cooling system is at operating temperature, the leak is then found sometimes it is obviously leaking from a coolant hose or cracked housing, failed gasket or water pump, sometimes the engines cooling system needs to be inspected from below or inspected using a mirror and flash light. If the coolant loss is still evasive dye can be added to the cooling system that may indicate the source of the leak. A mysterious coolant loss may even be a sign of a head gasket that is not sealing well. It is possible the water pump is leaking but don't jump to conclusions it may be as simple as a hose or seal.

Autozone has a loaner radiator pressure tester,in wich you can check for leaks ,be careful not to pump up the pressure past what your cap shows its rated for