Leaking Coolant 1999 Buick Century

2001 Buick CenturyI have a problem with my cooling system in my 1999 Buick Century Custom. I am leaking coolant. I tried stop leak, is not working. I can drive for long periods of time, open the radiator cap without any problem. It is cold to the touch and there is no pressure when I release the cap.


Sounds like your thermostat may be stuck in the open position as well as leaking coolant. Also the radiator cap may be faulty if no pressure is building or you have a large leak. You will need to use a cooling system pressure tester.

How to find leaking coolant

  • With the engine off,  Remove the radiator cap and attach the pressure tester
  • Pump up the tester to apply pressure on the system. Pressure should be the same as the radiator cap. (around 17-20 psi)
  • Look for the leak, put cardboard underneath to help if needed. If no external leak is found, remove spark plugs and look for coolant to come out spark plug holes.
  • Repair the leak
  • Pump up the tester again
  • Watch for the pressure to hold, this indicate no more leak in the system.

Coolant Description

Caution! Antifreeze can be added to raise the boiling point of the coolant, but too much will affect the freezing point. Do not use a solution stronger than 70 percent antifreeze, as the freeze level rises rapidly after this point. Pure antifreeze will freeze at -22°C (-8°F).

GM Goodwrench DEX-COOL® was developed in order to last for 240,000 km (150,00 miles) or 5 years, whichever occurs first. Follow the instructions in Draining and Filling Cooling System . Use only GM Goodwrench DEX-COOL® or HAVOLINE® DEX-COOL® when adding or changing the coolant.

A 50/50 mixture of ethylene glycol DEX-COOL® and water will provide the following protection:

  • Give freezing protection down to -37°C (-34°F)
  • Give boiling protection up to 129°C (265°F)
  • Protect against rust and corrosion
  • Help keep the proper engine temperature
  • Let the warning lights and gauges work as they should.