2007 Cadillac STS Owner's Manual - Page 400

By this time, the coolant level inside the coolant surge tank may be lower. If the level is lower, add more of the proper mixture to the coolant surge tank until the level reaches the FULL COLD/FROID line on the side of the coolant surge tank. 5. Then replace the pressure cap. Be sure the pressure cap is hand-tight and fully seated. Start the engine and allow it to warm up. How to Add Coolant to the Intercooler System Fill Neck (4.4L V8 STS-V Engine Only) 3. Fill the coolant surge tank with the proper DEX-COOL® coolant mixture, to slightly above the FULL COLD/FROID line on the side of the coolant surge tank. 4. With the coolant surge tank pressure cap off, start the engine and let it run until you can feel the upper radiator hose getting hot. The upper radiator hose is the largest of the hoses which comes out of the radiator, on the passenger side of the vehicle. Watch out for the engine cooling fans. If you have not found a problem yet, turn the engine off and allow it to cool down, then check to see if coolant is visible within the horizontal tube section of the fill neck. If coolant is not visible, add a 50/50 mixture of clean, drinkable water and DEX-COOL® coolant to the fill neck. Be sure the Intercooler System, including the Intercooler System pressure cap, is cool before doing so. See Engine Coolant on page 389 for more information. 400