I just replaced the upper and lower radiator hoses on my '91 300E. I also changed the thermostat.

I recommend that you premix a couple of gallons of 50/50 M-B antifreeze and distilled water. Then get yourself a piece of hose about 30" long. The ideal thing is to cut the metal ends off an old washing machine drain hose.

Open up the access panel to the front tow hook and you will see a drain petcock for the radiator. There is a nipple on the radiator that faces towards the wheel well. If you then look on the other side of the wheel well, you will find a rubber plug that will give you access to the nipple.

Remove the rubber plug and insert the hose from the outside, through the hole and onto the nipple. Place the other end of the hose in a shallow drain pan.

Remove the cap on the coolant tank to permit the coolant to drain better.

Now reach in and open the petcock with your fingers or use a long screw driver. (NOTE, When you close the petcock, do it finger tight only).

Coolant will drain into the pan.

After the coolant has stopped draining, remove the three bolts holding the cover over the thermostat and then loosen the clamp on the upper hose at the radiator end. Carefully twist the hose to get it loose from the radiator and take it off. Remove the other end of the hose from the cover for the thermostat.

Now loosen the clamps on the lower hose and work it loose.

Replace the thermostat with a new one and orient it the same way as the one you took out.

Install a new lower hose. Orient the clamps according to the marks on the clamp and the hose (if they are there). Tighten the clamps.

Put the upper hose on the radiator and slide the other end over the outlet on the cap for the thermostat.

Bolt the thermostat cover but don't over tighten. If the cover is not aluminum, get the new aluminum version before changing the hoses.

Orient the upper hose and clamps and tighten the clamps.

Remove the drain hose from the radiator.

Put the rubber plug back in the wheel well wall.

Tighten the petcock finger tight. If you use a screwdriver, don't over tighten.

Slowly pour the premixed coolant in the coolant tank. Allow it to work it's way back into the system.

At some point, you will not be able to put more coolant into the tank.

Start the car and let the coolant circulate.

After the thermostat opens, you should be able to add more coolant.

Turn off the engine.

Replace the cap on the coolant tank.

The next morning, top up if necessary.

I should have said that you should run the car with full heat on and the controls set to both upper and lower so that coolant is circulated through the heater core and the defroster. Do this before changing the coolant.

After you have finished, make sure you run the engine the same way to get full coolant circulation.