GM Astro/Safari 1985-1996 Repair Guide

Cooling System


See Figure 1

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Fig. Fig. 1: Cutaway view of a typical cooling system flow

For most of the vehicles covered by this guide (except 1996 which use a different type of coolant) you should inspect, flush and refill the engine cooling system with fresh coolant (antifreeze) at least once every 2 years or 30,000 miles (48,000 km). If the coolant is left in the system too long, it loses its ability to prevent rust and corrosion. If the coolant has too much water, it won't protect against freezing and it can boil-over in the summer.

The cooling systems on all 1996 vehicles were originally filled with silicate-free DEX-COOL® coolant meeting GM specification 6277M. The fluid is easily identified because of its orange color (instead of the green we have come to expect from most types of ethylene glycol antifreeze). If your cooling system is filled with DEX-COOL®, then no periodic service is required, other than fluid level checks, for 100,000 miles (161,000 km) or 5 years, whichever comes first. BUT if you add a silicated coolant to the system (even in small amounts) premature engine, heater core or radiator corrosion may result. In addition, the coolant will have to be changed sooner (30,000 miles/48,000 km or 2 years, just like other vehicles not using DEX-COOL®).


See Figure 2

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Fig. Fig. 2: On 1996 models, labels in the engine compartment warn you that special coolant is used

For 1985-95 vehicles use a good quality ethylene glycol antifreeze (one that will not effect aluminum), mixed with water until a 50-50 antifreeze solution is attained. Colder climates require more antifreeze to prevent freezing. Refer to the chart on the back of the antifreeze container.

In addition to the coolant, 1995 vehicles require the addition of 2 sealant pellets (GMSPO No. 3634621) whenever the entire system has been drained and is being refilled with fresh coolant.

As mentioned earlier in this information, 1996 vehicles were originally equipped with GM DEX-COOL® silicate-free coolant. GM does not recommended any other type of coolant for these vehicles. It is easily identified by its orange color.

In all instances, you should premix your coolant and water solution, to be sure you will get the proper ratio of coolant to water. Also, distilled water is preferred as tap water may contain minerals or additives that could be harmful to the cooling system.


See Figures 3 and 4

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Fig. Fig. 3: On all models, the coolant level should be checked through the coolant recovery tank ...

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Fig. Fig. 4: ... and if coolant is needed, it should be added to the tank

The coolant level should be checked EVERY TIME you open the hood.

When checking the coolant level, the radiator cap does not have to be removed, simply check the coolant recovery tank (normally found on the passenger's side of the engine compartment, next to the windshield wiper/washer fluid bottle).

Check the coolant recovery bottle (see through plastic bottle). With the engine Cold, the coolant should be at the ADD or COLD mark (recovery tank about 1 / 4 full). With the engine warm, the coolant should be at the FULL or HOT mark (recovery tank about 1 / 2 full). If necessary, add fluid to the recovery bottle.


See Figures 5 and 6

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Fig. Fig. 5: Cooling systems should be pressure tested for leaks periodically

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Fig. Fig. 6: The freezing/boiling points of your coolant can be checked using a simple, inexpensive antifreeze hydrometer

Never remove the radiator cap under any conditions while the engine is hot! Failure to follow these instructions could result in damage to the cooling system, engine and/or personal injury. To avoid having scalding hot coolant or steam blow out of the radiator, use extreme care whenever you are removing the radiator cap. Wait until the engine has cooled, then wrap a thick cloth around the radiator cap and turn it slowly to the first stop. Step back while the pressure is released from the cooling system. When you are sure the pressure has been released, press down on the radiator cap (still have the cloth in position) turn and remove the radiator cap.

Dealing with the cooling system can be a dangerous matter unless the proper precautions are observed. It is best to check the coolant level in the radiator when the engine is cold. All vehicles covered by this guide should be equipped with a coolant recovery tank which can be checked hot or cold (refer to the level check information earlier in this section). Always be certain that the filler caps on both the radiator and the recovery tank are closed tightly.

Never add coolant to a hot engine unless it is running. If it is not running you run the risk of cracking the engine block.

It is wise to pressure check the cooling system at least once per year. If the coolant level is chronically low or rusty, the system should be thoroughly checked for leaks.

A simple and inexpensive hydrometer should be available in most parts stores to help you test the antifreeze in your system. It will tell you the boiling and freezing points of ethylene glycol antifreeze based on specific gravity. Although this is good in helping to determine the temperature protection it will give your engine, it does NOT tell you how old the coolant it. Even if it tests good for temperature protection, the coolant may no longer be providing corrosion protection and should be changed if you are unsure of its age. Again, the rules on DEX-COOL® are a little different (considering how much longer it lasts and that the ethylene glycol hydrometer readings may not apply) BUT, the principle is the same. If you suspect the coolant in a 1996 vehicle is older than the manufacturer recommends, OR if you think silicate-based coolant may have been added to it, you should probably drain, flush and refill the system.

The pressure cap should be examined for signs of age or deterioration. The fan belt and other drive belts (if equipped) should be inspected and adjusted to the proper tension. (See the information on drive belts earlier in this section.)

Hose clamps should be tightened, and soft or cracked hoses replaced. Damp spots, or accumulations of rust or dye near hoses, water pump or other areas, indicate possible leakage, which must be corrected before filling the system with fresh coolant. (For more information, please refer to Hoses, earlier in this section.)

Checking the Radiator Cap Seal

See Figure 7

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Fig. Fig. 7: Be sure the rubber gasket on the radiator cap has a tight seal

While you are checking the cooling system, check the radiator cap for a worn or cracked gasket. It the cap doesn't seal properly, fluid will be lost and the engine will overheat.

Worn caps should be replaced with a new one.

Checking the Radiator for Debris

See Figure 8

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Fig. Fig. 8: Periodically remove all debris from the radiator fins

Periodically clean any debris - leaves, paper, insects, etc. - from the radiator fins. Pick the large pieces off by hand. The smaller pieces can be washed away with water pressure from a hose.

Carefully straighten any bent radiator fins with a pair of needle-nose pliers. Be careful - the fins are very soft. Don't wiggle the fins back and forth too much. Straighten them once and try not to move them again.


See Figures 9, 10 and 11

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Fig. Fig. 9: To prevent a mess when draining the radiator, place a plastic tube over the radiator petcock

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Fig. Fig. 10: When refilling the system, pour coolant directly into the radiator, then ...

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Fig. Fig. 11: ... top off using the recovery tank (once the sealed radiator is at normal operating temperature)

When draining the coolant, keep in mind that cats and dogs are attracted by ethylene glycol antifreeze, 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. To avoid injuries from scalding fluid and steam, DO NOT remove the radiator cap while the engine and radiator are still HOT.

  1. When the engine is cool, remove the radiator cap using the following procedures.
    1. Slowly rotate the cap counterclockwise to the detent.
    3. If any residual pressure is present, WAIT until the hissing noise stops.
    5. After the hissing noise has ceased, press down on the cap and continue rotating it counterclockwise to remove it.

  3. Place a fluid catch pan under the radiator, open the radiator drain valve and, if access is possible, remove the engine drain plugs, then drain the coolant.

To help prevent a mess when coolant splashes over everything and drips from all points at the front of the vehicle, try placing a short rubber tube over the radiator petcock before opening it. The route the tube down from the vehicle to the drain pan.

  1. Close the drain valve and, if removed, install the engine drain plugs.
  3. Empty the coolant reservoir and flush it.
  5. Using the correct mixture (AND TYPE, refer to the fluid recommendations earlier in this section if you are unsure) of antifreeze, fill the radiator to about 1 / 2 in. (13mm) from the bottom of the filler neck.
  7. Start the engine and allow it to idle as the engine warms-up. As the thermostat is opened, air which was trapped in the engine should be expelled, causing the fluid level in the radiator to drop. Add fresh coolant/water mixture until the level reaches the at the bottom of the filler neck.
  9. For 1995 vehicles, add 2 sealant pellets (GMSPO part No. 3634621) to coolant mixture in the radiator. This MUST be done to prevent premature water pump leakage. DO NOT add the pellets to the recovery bottle since this might prevent the coolant system from operating properly.
  11. Add some of the coolant/water mixture to the coolant tank, but don't go above the ADD or COLD mark at this time.
  13. Install the radiator cap (make sure the arrows align with the overflow tube).
  15. Run the engine until it reaches the operating temperatures, then check the recovery tank and add fluid (if necessary).


There are various methods to flush the cooling system, including power flushing equipment or adapters to attach your garden hose. If special equipment is to be used (such as a back flusher), follow the equipment manufacturer's instructions closely. Also, carefully read the bottle of any flushing solution, to make sure it is compatible with your cooling system components and the type of antifreeze used.

Most flushing compounds attack metals and SHOULD NOT remain in the cooling system for more than a few minutes. Be sure to use a neutralizer in the cooling system IMMEDIATELY after a descaling solvent has been used. Keep in mind that for extremely hard, stubborn coatings, such as lime scale, a stronger solution may be necessary. BUT, the corrosive action of the stronger solution will affect the thin metals of the radiator, thereby reducing its operating life. A COMPLETE flushing and rinsing is mandatory if this is attempted.

  1. Refer to the Drain and Refill procedures in this section, then drain the cooling system.
  3. Close the drain valve and install the engine drain plugs, then add sufficient water to the cooling system.
  5. Run the engine, then drain and refill the system. Perform this procedure several times, until the fluid (drained from the system) is clear.
  7. Empty the coolant reservoir and flush it.
  9. Properly refill the engine cooling system with the correct type and mixture of coolant for your vehicle. Refer to the fluid recommendations and the fluid refill procedures found earlier in this section.