Occasionally your automobile’s coolant reservoir will begin to overflow. This is not something to ignore, but it isn’t necessarily a difficult problem to fix either.
Step 1 - Check for a Broken or Defective Radiator Cap
If your radiator cap has gone bad, it will allow too much coolant to pass by the cap and overflow around it. It’s also the cheapest part to replace. However, if it isn’t the radiator cap, it could be other problems, some more difficult than others to fix.
Step 2 - Check the Thermostat
If the thermostat is going bad, your radiator won’t regulate properly and the amount of liquid allowed to pass through at any given time may be too little or too much. Check and have it replaced if needed.
Step 3 - Check the Water Pump
If the water pump is not operating correctly, and your coolant reservoir is overflowing, there may be too much coolant being pumped through and pressure may be ultimately leading to your reservoir overflowing. Replace it if needed.
Step 4 – Replace Radiator
If at this point your coolant reservoir is still overflowing, the entire radiator may need to be replaced. If this is the case, you can be sure that it will cost you more than just a couple of dollars for parts and labor, and it is recommended that you have the entire radiator replaced by a professional. This is the most unlikely of all the scenarios.