Chevrolet 1979 Light Duty Truck Owner's Manual page 88

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Wait until the pressure is relieved (indicated by a hissing
sound), then press down on the cap and continue to tum it
to the left.
CAUTION: To help avoid the danger of being burned, do not remove
the radiator cap while the engine and radiator are still hot. Scalding fluid
and steam can be blown out under pressure if the cap is taken off too
soon.
2.
When the cap is removed, run the engine until the upper radiator
hose is hot (this shows that the thermostat is open and the coolant
is flowing through the system).
3. Stop the engine and open the radiator drain valve to drain the
coolant. (Drainage may be speeded by removing the drain plugs
in the block.)
4 . Close the drain valve (install block drain plugs, if removed). Add
water until the system is filled and run the engine until the upper
radiator hose is hot again.
5. Repeat steps 3 and 4 several times until the drained liquid is nearly
colorless.
6. Drain the system and then close the radiator drain valve tightly.
(Install block drain plugs, if removed.)
7. Disconnect all hoses from the coolant recovery tank. Remove the
tank and pour out any fluid. Scrub and clean the inside of the tank
with soap and water. Flush it well with clean water and drain.
Reinstall the tank and hoses.
8. Add enough ethylene glycol coolant (meeting GM Specification
1899-M) and water to provide the required cooling, freezing, and
corrosion protection. Use at least a 50 percent solution, -34•F
(-37•C), but no more than a 70 percent solution. Fill the radiator
to the base of the filler neck and fill the coolant recovery tank to
the "Cold Level" mark. Install recovery tank cap.
9 . Run the engine, with the radiator cap removed, until the upper
radiator hose is hot.
10. With the engine idling, add coolant to the radiator until it reaches
the bottom of the filler neck. Install the radiator cap, making sure
that the arrows on the cap line up with the overflow tube.
It is the owner's responsibility to:
•
Maintain cooling system freeze protection at -20•F (-29.C) to
ensure protection against corrosion and loss of coolant from
boiling. This should be done even if freezing temperatures are not
expected.
•
Add ethylene glycol base coolant that meets GM Specification
1899-M when coolant has to be added because of coolant loss or
to provide added protection against freezing at temperatures lower
than -20"F (-29.C); -35•F (-37•c in Canada).
NOTICE: Alcohol or methanol base coolants or plain water alone
should not be used in your vehicle at any time. They will boil at a lower
point than that at which the hot light indicator (or temperature gage)
works, and they do not provide proper protection against corrosion.
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