How to Repair a 1990 BMW 535I Radiator

1. Crank the BMW's engine, and allow it to warm so the radiator can move coolant through the cooling system and engine. Observe the radiator's surface area, including the tubes, fins and hose connectors for spewing, seeping or weeping coolant. Observe the area under the BMW for coolant on the ground, which might provide a clue as to the location of the leak. Finally, turn off the vehicle and clean the radiator's surface of any leaves, dirt or other debris that might be obscuring a leak. Rocks and other debris flying at the radiator from the road do more damage to a BMW 535i plastic radiator than a brass radiator.
2. Unscrew metal rings holding a ripped or torn radiator hose in place after the engine has cooled off. Pull the hose away from the connectors, and brush away any debris. Place the new hose on the connector openings, and replace the metal rings, tightening properly.
3. Open the radiator by removing the radiator cap, and pour in a bottle or can of radiator sealant. Radiator sealant comes in both pellet and powder form, and both forms work the same way --- by swelling into leaks to fill them. Drive the BMW for 30 minutes to allow the sealant to circulate through the radiator.
4. Stop the engine, and allow it to cool. Drain all of the coolant from the radiator, and remove it from the BMW. Place the air-free plastic welder over the leak area until it is heated all the way through. Place the air-free welder over the plastic welding rod to melt it into the leak until it begins to take on the color of the radiator. Allow the weld job to cool.
5. Stop the engine, and allow the BMW to cool. Open the radiator plug, drain the coolant, and take the radiator out of the vehicle. Spray water or air to clean any remaining debris from surface and hose connectors. Sand the area of the leak to prep for welding. Heat the area to be repaired with an air-free plastic welder. For surface holes, fill with epoxy. For broken hose connectors or seam leaks, melt a plastic welding rod over the area, and press the broken surfaces together. Both methods require time to set before reinstalling the radiator and refilling the system.