Chevrolet Blazer/Jimmy 1969-1982 Repair Guide

Cooling System


Since the cooling system is pressurized, the radiator cap must not be removed unless the engine has cooled. To do otherwise involves the risk of being scalded by steam. To check the coolant level:


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Fig. Fig. 1 To fill the radiator, remove the cap by pressing down and turning it counterclockwise

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Fig. Fig. 2 Use a funnel to avoid spillage when adding coolant to the system

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Fig. Fig. 3 To add coolant to the recovery system tank, remove the cap ...

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Fig. Fig. 4 ... then add fluid until the level indicated on the side of the tank is reached

Without Coolant Recovery System
  1. Allow the engine to cool.
  3. Turn the cap counterclockwise to the detent. It is a good idea to wear a glove or use a thick rag for protection.
  5. If there is still pressure in the system, its escape will make a hissing sound.
  7. When there is no further hissing, press down on the cap and continue turning it counterclockwise to remove.
  9. The coolant level should be 1 1 / 4 in. below the bottom of the filler neck hot, and 3 in. below cold. Overfilling will result in coolant loss due to heat expansion.
  11. If the coolant needs to be replenished, add equal amounts of anti-freeze and water.

Never add large quantities of cold water to a hot engine. A cracked engine block may result.

Anti-freeze solution 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.

  1. If the coolant level is frequently low, refer to the Troubleshooting charts in for diagnosis of the problem. Also see for coolant draining and refilling.
  3. Replace the radiator cap.

With Coolant Recovery System

If you have a coolant recovery system, coolant level checking is easy. The level in the plastic catch tank alongside the radiator should be between the FULL COLD and FULL HOT marks with the engine idling at normal operating temperature. The radiator will be full. Add coolant only to the tank; don't remove the radiator cap. If you do remove the cap, you will allow air into the system. Steps 6 and 7 "Without Coolant Recovery System" apply to this type, too.


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Fig. Fig. 5 To drain the radiator coolant, open the petcock located at the bottom of the radiator

The cooling system in your vehicle 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 (48,000 km) or once a year.

When draining the coolant, keep in mind that cats and dogs are attracted by ethylene glycol anti-freeze, and are quite likely to drink any that is left in an uncovered container or in puddles on the ground. This will prove fatal in sufficient quantity. Always drain the coolant into a sealable container. Coolant should be reused unless it is contaminated or several years old.

  1. Drain the existing anti-freeze and coolant. Open the radiator and engine drain petcock or disconnect the bottom radiator hose at the radiator outlet.
  3. Close the petcock or reconnect the lower hose and fill the system with water-hot water if the system has just been run.
  5. Add a can of quality radiator flush to the radiator or recovery tank, following any special instructions on the can.
  7. Idle the engine as long as specified on the can of flush, until the upper radiator hose gets hot.
  9. Drain the system again. There should be quite a bit of scale and rust in the drained water.
  11. Repeat this process until the drained water is mostly clear.
  13. Close the petcock and connect all hoses.
  15. Flush the coolant recovery reservoir with water and leave empty.
  17. Determine the capacity of your vehicle's cooling system. Add a 50/50 mix of ethylene glycol anti-freeze and water to provide the desired protection.
  19. Run the engine to operating temperature, then stop the engine and check for leaks. Check the coolant level and top up if necessary.
  21. Check the protection level of your anti-freeze mix with an anti-freeze 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°F (-15°C), for example.