If you discover engine coolant running out from under your car, you may have a radiator leak. If the leak is small, you can probably repair it using the tips given here.
Step 1: Add stop-leak coolant Add a stop-leak coolant to the radiator for a more long-term fix. Be sure to follow the manufacturer's directions.
Step 2: Add mustard or pepper Try adding 2 tablespoons of mustard powder or ground black pepper to your engine coolant if you have a small radiator leak. The mustard or pepper will migrate to the leak and form a temporary seal.
TIP: Adding mustard or pepper is only a temporary fix, and must be repeated each time you turn off the engine.
Step 3: Consider welding Consider welding cracks or multiple radiator leaks if you have the expertise and equipment. Otherwise, you will probably be better off replacing the radiator. Enjoy a stress-free ride.
Step 4: Check radiator hose Pull the car over to the side of the road if you are driving it, and check for a broken radiator hose. In an emergency, you may be able to repair it with duct tape.
FACT: Plastic-tank radiators are nearly impossible to fix. Copper-and-brass models, however, are fixable.