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

Freeze Plugs


On most cast iron blocks, round metal plugs are used to seal coolant jackets. These plugs allow for a certain amount of water and block expansion should water (without anti-freeze) ever be left in the coolant system. Although the cooling system should NEVER be filled with plain water only, an emergency and unavailability of coolant could force the situation to occur.

In the event that water only is placed in the cooling system and the engine is subject to sub-freezing temperatures, it is likely that the water will freeze and expand. It is also quite possible that the block will expand and crack. If you are lucky though, the expansion may only cause freeze plugs to become dislodged.

During engine block overhaul, it is often standard procedure to remove and replace all of the freeze plugs.


See Figures 1 and 2

  1. Disconnect the negative battery cable, then properly drain the engine cooling system.
  3. If equipped, remove the engine coolant drain plugs (located at the bottom of the block usually near the oil pan rail) and drain the coolant from the block. If the engine is not equipped with coolant drain plugs, drill a small hole in the leaking freeze plug and allow any remaining coolant to drain.
  5. Remove any components that restrict access to the freeze plug or, if necessary, remove the engine from the vehicle for access to the freeze plug(s).

Always wear proper eye protection when using a chisel, especially when attempting to dislodge a freeze plug.

Click image to see an enlarged view

Fig. Fig. 1: Using a punch and hammer, the freeze plug can be cocked and loosened in the block

Click image to see an enlarged view

Fig. Fig. 2: Once the freeze plug has been cocked, it can be removed from the block

  1. Using a chisel, tap the bottom edge of the freeze plug to cock it in the bore. Remove the plug using pliers, but be careful not to score the block or the new freeze plug may not fit well. An alternate method is to drill an 1 / 8 in. hole in the plug and remove it using a dent puller.

To install:
  1. Clean the bore of any debris and make sure it is free of any deep scratches which could cause a leak.

Some auto part stores may offer easy to install freeze plugs consisting of a grommet with metal plates and an adjustment bolt. These plugs are positioned, then the bolt is tightened to expand the grommet sealing the block bore. Although these might be handy to get the vehicle home quickly, they should not be installed as a permanent fix.

  1. Freeze plugs are interference fitted to the block. Make sure you have the proper plug size and an equalled sized driver. The proper sized driver will ease the installation process by preventing the plug from cocking in the bore as it is driven into position.
  3. Coat the plug with sealant, then position it to the bore and drive it into position.
  5. Install the interfering components or the engine, as applicable.
  7. Connect the negative battery cable and properly refill the engine cooling system, then check for leaks.