GM Buick/Oldsmobile/Pontiac/Full-Size 1975-1990 Repair Guide

Cooling System


The efficiency of the radiator can be seriously impaired by blockage of the radiator fins. Leaves, insects, road dirt and paper are common obstacles to fresh air entering your radiator and doing its job.

Large pieces of debris, leaves and large insects can be removed from the fins by hand. The smaller pieces can be washed out with water pressure from a garden hose. This is often a neglected area of auto maintenance, so do a thorough job.

Bent radiator fins can be straightened carefully with a pair of needlenosed pliers. The fins are soft, so don't wiggle them; move them once.

Anytime you check the coolant level, check the radiator cap as well. A worn or cracked gasket can mean improper sealing, which can cause lost coolant, lost pressure, and engine overheating (the cooling system is pressurized and the radiator cap has a pressure rating above the pressure of the system).

A worn cap should be replaced with a new one. Make sure the new cap has the proper pressure rating for your vehicle's system; this is usually marked on the standard factory cap. Never buy a cap having a rating less than the pressure of your vehicle's system.

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.


A quality, ethylene glycol coolant containing corrosion inhibitors and compatible with aluminum engine parts, meeting GM Specification 1825-M should be used. Antifreeze concentration should be high enough to maintain freezing protection down to -34°F (-37°C).


It is best to check the coolant level when the engine and radiator are cool. Buick, Oldsmobile and Pontiac vehicles covered in this guide are equipped with coolant recovery tanks connected by hoses to the radiator and mounted on the inner fender skirt. If the coolant level is at or near the FULL COLD (engine cold) or the FULL HOT (engine hot) lines on the tank, the level is satisfactory.

Check the freezing protection rating at least twice a year, preferably in mid-fall and mid-spring. This can be done with an antifreeze tester, the use of which is detailed under Cooling System in this section.

Never add coolant to a hot engine. Stop the engine and allow it to cool. Then, start it to circulate coolant uniformly through the block and add coolant slowly as the engine idles. Otherwise you risk cracking the block. The coolant recovery tank is the only accurate place to check the coolant level; however, coolant can be added to either the tank or directly to the radiator. NEVER REMOVE THE RADIATOR CAP UNTIL THE ENGINE HAS HAD AMPLE TIME TO COOL TO BELOW OPERATING TEMPERATURE.

If you find the coolant level low, add a 50/50 mixture of ethylene glycol based antifreeze and clean water. Do not add straight water unless you are out on the road and in emergency circumstances; if this is the case, drain the radiator and replenish the cooling system with an ethylene glycol mix at the next opportunity. Modern ethylene glycol antifreezes are special blends of anti-corrosive additives and lubricants that help keep the cooling system clean and help lubricate the water pump seal, which is why they are recommended by the manufacturers.


See Figures 1, 2, 3, 4, 5 and 6

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 or once every two years.

  1. Drain the existing antifreeze and coolant. Open the radiator and engine drain petcocks (located near the bottom of the radiator and on the side of the engine block, down low, 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.

  1. Close the petcock or reconnect the lower hose and fill the system with water; hot water, if possible, if the engine has been run. Fill slowly with the engine idling.
  3. Add a can of quality radiator flush to the radiator, following any special instructions on the can.
  5. Idle the engine as long as specified on the can of flush, or until the upper radiator hose gets hot.
  7. Drain the system again. There should be quite a bit of scale and rust in the drained water.
  9. Repeat the rinsing process until the drained water is almost completely clear.
  11. Close all petcocks and connect all hoses.
  13. Flush the coolant recovery reservoir with water and leave empty.
  15. Determine the capacity of your vehicle'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.
  17. Run the engine to operating temperature, then stop the engine and check for leaks. Check the coolant level and top up if necessary.

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Fig. Fig. 1: To drain the coolant, first locate the radiator drain cock

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Fig. Fig. 2: Loosen the drain cock to drain the coolant from the radiator

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Fig. Fig. 3: Locate and remove the engine drain plug

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Fig. Fig. 4: Before filling the cooling system, be sure the engine drain plug is reinstalled and the radiator drain cock is closed

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Fig. Fig. 5: Once the radiator has been filled, fill the coolant reservoir to the proper level

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Fig. Fig. 6: Recheck the coolant level after the vehicle has reached operating temperature