See Figures 1 and 2
The proper coolant for your GM truck is a 50/50 mix of ethylene glycol antifreeze and water. Alcohol or methanol base coolants are not recommended. Antifreeze solutions should be used, even in summer, to prevent rust and to take advantage of the solution's higher boiling point compared to plain water. This is imperative on air conditioned trucks; the heater core can freeze if it isn't protected.
See Figures 3, 4, 5 and 6
The coolant level should be checked at each fuel stop, ideally, to prevent the possibility of overheating and serious engine damage. If not, it should at least be checked once each month.
The cooling system was filled at the factory with a high quality coolant solution that is good for year around operation and protects the system from freezing down to -20°F (-32°F in Canada). It is good for two full calendar years or 24,000 miles, whichever occurs first, provided that the proper concentration of coolant is maintained.
The 1973 and later cooling system differs slightly from those used on 1970-72 trucks. The 1973 and later system incorporates a plastic expansion tank connected to the radiator by a hose from the base of the radiator filler neck. The hot coolant level on 1973 and later trucks should be at the FULL HOT mark on the expansion tank and the cold coolant level should be at the FULL COLD mark on the tank. Do not remove the radiator cap to check the coolant level on 1973 and later trucks. On 1970-72 trucks, the cold coolant level should be approximately 3" below the bottom of the filler neck, and the hot level should be 1 / 2 in. below the bottom of the filler neck.
To check the coolant level:
- On 1973 and later models, check the level on the see-through expansion tank. On earlier models it will be necessary to CAREFULLY remove the radiator cap.
- Check the level and, if necessary, add coolant to the proper level. Use a 50/50 mix of ethylene glycol antifreeze and water. Alcohol or methanol base coolants are not recommended. Antifreeze solutions should be used, even in summer, to prevent rust and to take advantage of the solution's higher boiling point compared to plain water. This is imperative on air conditioned trucks; the heater core can freeze if it isn't protected. On 1974 and later models, coolant should be added through the coolant recovery tank, not the radiator filler neck.
- Replace the cap.
- Each year the cooling system should be serviced as follows:
- Wash the radiator cap and filler neck with clean water.
- Check the coolant for proper level and freeze protection.
- Have the system pressure tested (15 psi).
If a replacement cap is installed, be sure that it conforms to the original specifications.Tighten the hose clamps and inspect all hoses. Replace hoses that are swollen, cracked or otherwise deteriorated. Clean the frontal area of the radiator core and the air conditioning condenser, if so equipped.
DRAINING, FLUSHING AND REFILLING
See Figure 7
The cooing system in your car accumulates some internal rust and corrosion in its normal operation. A simple method of keeping the system clean is known as flushing the system. It is performed by circulating a can of radiator flush through the system, and then draining and refilling the system with the normal coolant. Radiator flush is marketed by several different manufacturers, and is available in cans at auto departments, parts stores, and many hardware stores.
This operation should be performed every 30,000 miles or once a year.To flush the cooling system:
- Drain the existing antifreeze and coolant. Open the radiator and engine drain petcocks (located near the bottom of the radiator and engine bloc, respectively), or disconnect the bottom radiator hose at the radiator outlet.
Before opening the radiator petcock, spray it with some penetrating oil. Be aware that if the engine has been run up to operating temperature, the coolant emptied will be HOT.
- Close the petcock or reconnect the lower hose and fill the system with water; hot water if the system has just been run.
- Add a can of quality radiator flush to the radiator or recovery tank, following any special instructions on the can.
- Idle the engine as long as specified on the can of flush, or until the upper radiator hose gets hot.
- Drain the system again. There should be quite a bit of scale and rust in the drained water.
- Repeat this process until the drained water is mostly clear.
- Close all petcocks and connect all hoses.
- Flush the coolant recovery reservoir with water and leave empty.
- Determine the capacity of your car's cooling system (see Capacities specifications in this guide). Add a 50/50 mix of ethylene glycol antifreeze and water to provide the desired protection.
- Run the engine to operating temperature, then stop the engine and check for leaks. Check the coolant level and top up if necessary.
- Check the protection level of your antifreeze mix with an antifreeze tester (a small, inexpensive syringe-type device available at any auto parts store). The tester has five or six small colored balls inside, each of which signify a certain temperature rating. Insert the tester in the recovery tank and suck just enough coolant into the syringe to float as many individual balls as you can (without sucking in too much coolant and floating all the balls at once). A table supplied with the tester will explain how many floating balls equal protection down to a certain temperature (three floating balls might mean the coolant will protect your engine down to 5 degrees F, for example).