GM S10/S15/Sonoma Pick-Ups 1982-1993 Repair Manual




See Figures 1, 2, 3 and 4

Upper and lower radiator hoses along with the heater hoses should be checked for deterioration, leaks and loose hose clamps at least every 15,000 miles. It is also wise to check the hoses periodically in early spring and at the beginning of the fall or winter when you are performing other maintenance. A quick visual inspection could discover a weakened hose which would have left you stranded if it had remained unrepaired.

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Fig. Fig. 1: The cracks developing along this hose are a result of age-related hardening

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Fig. Fig. 2: A hose clamp that is too tight can cause older hoses to separate and tear on either side of the clamp

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Fig. Fig. 3: A soft spongy hose (identifiable by the swollen section) will eventually burst and should be replaced

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Fig. Fig. 4: Hoses are likely to deteriorate from the inside if the cooling system is not periodically flushed

Whenever you are checking the hoses, make sure the engine and cooling system is cold. Visually inspect for cracking, rotting or collapsed hoses, replace as necessary. Run your hand along the length of the hose. If a weak or swollen spot is noted when squeezing the hose wall, the hose should be replaced.


  1. Remove the radiator pressure cap.

Never remove the pressure cap while the engine is running or personal injury from scalding hot coolant or steam may result. If possible, wait until the engine has cooled to remove the pressure cap. If this is not possible, wrap a thick cloth around the pressure cap and turn it slowly to the stop. Step back while the pressure is released from the cooling system. When you are sure all the pressure has been released, still using the cloth, turn and remove the cap.

  1. Position a clean container under the radiator drain cock and/or engine drain plug, then open the drain and allow the cooling system to empty to an appropriate level. For some upper hoses only a little coolant must be drained. To remove hoses positioned lower on the engine, such as the lower radiator hose, the entire cooling system must be drained.

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 may be reused unless it is contaminated or several years old.

  1. Loosen the hose clamps at each end of the hose requiring replacement. Clamps are usually either of the spring tension type (which require pliers to squeeze the tabs and loosen) or of the screw tension type (which require screw or socket drivers to loosen as applicable). Pull the clamps back on the hose away from the connection.
  3. Twist, pull and slide the hose off the fitting taking care not to damage the neck of the component from which the hose is being removed.

If the hose is stuck at the connection, do not insert a screwdriver or other sharp tool under the hose end in an effort to free it, as the connection and/or hose may become damaged. Heater connections can be easily damaged by such a procedure. If the hose is to be replaced, use a single-edged razor blade to make a slice along the portion of the hose which is stuck on the connection, perpendicular to the end of the hose. Do not cut deep so as to prevent damaging the connection. The hose can then be peeled from the connection and discarded.

  1. Clean both hose mounting connections. Inspect the condition of the hose clamps and replace them, if necessary.

To install:
  1. Dip the ends of the new hose into clean engine coolant to ease installation.

When replacing the heater hoses, maintain a 11/2in. (38mm) clearance between the hose clip-to-upper control arm and between the rear overhead heater core lines-to-exhaust pipe.

  1. Slide the hose clamps over the replacement hose and slide the hose ends over the connections into position.

Draw the hoses tight to prevent sagging or rubbing against other components; route the hoses through the clamps as installed originally. Always make sure that the hose clamps are beyond the component bead and placed in the center of the clamping surface before tightening them.

  1. Position and secure the clamps at least 1 / 4 in. from the ends of the hose. Make sure they are located inside the raised bead of the connector.
  3. Close the radiator or engine drains and properly refill the cooling system with the clean drained engine coolant or a suitable 50/50 mixture of ethylene glycol coolant and water.
  5. If available, install a pressure tester and check for leaks.
  7. Leave the radiator cap off, then start and run the engine to normal operating temperature. When the engine is at operating temperature and the thermostat has opened, continue to fill the radiator until the level stabilizes just below the filler neck.
  9. Install the radiator pressure cap and check the clamped hose ends for leaks.
  11. Shut the engine OFF and allow the engine to cool. Once the engine has cooled, check for proper coolant level in the overflow tank and add, as necessary.