2009 Hummer H3x Owner's Manual - Page 260

5-24 Service and Appearance Care else until it cools down. If coolant is visible but the coolant level is not at or above the FULL COLD mark, add a 50/50 mixture of clean, drinkable water and DEX-COOL coolant at the coolant recovery tank, but be sure the cooling system is cool before this is done. The vehicle must be on a level surface. When the engine is cold, the coolant level should be at FULL COLD, or a little higher. When the engine is warm, the level could be above the FULL COLD level. When the engine is cold, the coolant level should be at least up to the FULL COLD mark. If it is not, there could be a leak in the cooling system. Checking Coolant The vehicle must be on a level surface when checking the coolant level. How to Add Coolant to the Recovery Tank { CAUTION You can be burned if you spill coolant on hot engine parts. Coolant contains ethylene glycol and it will burn if the engine parts are hot enough. Do not spill coolant on a hot engine. Notice: This vehicle has a specific coolant fill procedure. Failure to follow this procedure could cause the engine to overheat and be severely damaged. When the coolant in the coolant recovery tank is at the FULL COLD mark, start the vehicle. If coolant is needed, add the proper DEX-COOL coolant mixture at the coolant recovery tank. The coolant recovery tank cap has this symbol on it. It is located toward the rear of the engine compartment on the passenger side of the vehicle. See Engine Compartment Overview on page 5-10 for more information on location. Check to see if coolant is visible in the coolant recovery tank. If the coolant inside the coolant recovery tank is boiling, do not do anything