ok well first and formost step one would be that the cooling system would need to be drained and flushed includeing overflow bottle if you have one. i would suggest reverse flushing the radiator so that any rubbish in the top of the radiator is not pushed towards the bottom and block anything, to do this remove the radiator turn it upside down jam the garden hose in the lower radiator hose hole and let the hose rip. once done reinstall the radiator with hoses disconected, remove a heater hose from the back of the block if it is easy to get at if not remove your thermostste houseing (probably due to replace thermostate anyway) do the same wit the garden hose in the thermostate houseing to flush the entire engine, or fluch through the heater hose which ever option you choose.
ok now onto the easy part one you have flushed the system connect all hoses back up and put thermostate houseing back on, turn your heater to hot and fan to full blast, pour coolant/water into radiator untill radiator it full !!!!LEAVE RADIATOR CAP OFF!!!! this is very important to bleed the system properly.
next fill a 2Ltr soft drink bottle up with water or coolant which ever you are going to run. start the car and let idle untill thermostate opens keep and eye on radiator water level and top up as the air is being bled from the system once the water level is fairly consistant (topping up has not been done for at least 1 minute) place the 2Ltr bottle upside down over the radiator car hole ensureing there is a tight seal and squeeze the bottle slightly and release this will help to force out anymore trapped air pockets in the system and will show you if the system does infact require further bleeding. be carfull as the bottle will get very hot after some time. once the system is fully bled replace the radiator cap and top the overflow up to full line, go for a drive and check temp gauge to ensure the system is working correctally, check your heater and make sure it is infact heating and not blowing cold air, if it is you will have to flush the heater core to remove any foreign matter blocking it.
some helpfull hints.
if you are running only water in your system you will allways have some sort of an overheating problem remember that water evaporates and it will cause steam pockets withing the cooling system.
if you have allways had a car that runs a little on the hotter side then normal try adding a bottle of lucas super coolant or redline water wetter they help to neutralise the water in the system from turning to steam.
remember to check your cooling system at every service interval just to save any headaches that may arise later on.
allways adress a small coolant leak weater it's from a hose gasket or alot of dissapearing water asap, a little water lose and turn into a major problem.
if you have a blown headgasket stop driveing and fix it you will indeed destroy your engine if on the oil side you will require the oil pan and rocker cover to be removed and whole engine detoxed to get rid of all the water which can be a nightmare for any body mechanic or not, if on the cylinder side you can cause major damage to piston rings, valved etc if bad enough you could hydraulic the engine and snap a con rod or crank.
in the mbs the cooling system was never the greatest on a longer then normal run suggestions would be to upgrade to an aftermarket thermo fan, replace the termostate to a colder type and remove jiggler pin or uprage radiator to something with a thicker core (would need to be custom built).
last and not least never ever mix differnt types of coolant together do not mix different brands, all brands and types are differnt, meaning green doesnt mix with red coolant and TYPE A doesnt mix with TYPE B coolant, be aware of your required coolant if you have trouble remebering write your part numbers down on a note pad and store it in the glovebox.
