50/50: STILL THE BEST MIX 
Duramax radiator and cooing system maintenance tip can save money for pickup fleets
The GM heavy duty 6.6L Duramax LMM owner’s manual supplement says to change radiator coolant every 5 years or 150,000 miles.
But Rod Halsten, a GM master technician and long-time diesel mechanic, says to let the plastic overflow reservoir be your guide.
“If the coolant is red/pink, there’s no need to flush the system. If it’s light brown, like that in Big Red, it’s getting time for a radiator flush and coolant change.”
“If the coolant reservoir shows a dark ring around the top level or the fluid is brown, it’s really run its course and needs to be changed immediately,” says Halsten.
Halsten used Mobil Delvac Extended Life Coolant/Antifreeze when he flushed the cooling system in Big Red. Mobil Delvac’s coolant, which uses an Organic Acid Technology (OAT) formula, is good for 600,000 miles.
Barkley techs used a MotorVac automated system to do the radiator flush and coolant exchange.
The machine swapped 4-1/2 gallons in about 5 minutes once it was connected to the truck’s upper radiator hose. Fast and efficient. Perfect for the fleet shop.
“Water is the best coolant, but it creates rust and scale, which plugs the cooling system and heater cores. Antifreeze is the best protectant for a pickup’s cooling system, but it doesn’t dissipate heat well,” explains Halsten.
“That’s why a 50/50 mix of distilled water and antifreeze works best.”
