Cylinder Head Cup Plug Coolant Leak - keywords 4.8 5.3 5.7 6.0 L59 LM4 LM7LQ4 LQ9 LR4 LS1 LS6 sealer #PIP3018A - (Jun 15, 2005)
Cylinder Head Cup Plug Coolant Leak
2004-2005 Buick Rainier

2004-2005 Cadillac CTS-V

2003-2005 Cadillac Escalade

2003-2005 Chevrolet Corvette

2004-2005 Pontiac GTO

The following diagnosis might be helpful if the vehicle exhibits the symptom(s) described in this PI.

The customer concern may be a coolant leak.

During diagnosis the dealer will find a leak at a cylinder head cup plug.

If there is evidence of a coolant leak at the cylinder head cup plugs, the area should be cleaned and inspected to determine if an actual leak is present or if it was only a coolant stain. Some engines are built with cooling system sealing tabs. If only a stain is present, it may be the result of the cup plug seeping during the first 15 minutes of operation when the engine was new. The seepage may have occurred before the factory installed coolant tabs dissolved and sealed the plug to cylinder head area. If an actual leak is present, the cooling system should be drained, refilled with a 50/50 DEX-COOL mixture and 4 small sealer tabs. Small coolant tabs are available in packages of 5 (4 oz. each) and the part number is 12378254 (in Canada, use P/N 10953473 and add 1 1/2 pellets). After filling the cooling system, the vehicle should be operated for at least 15 minutes so the area can be inspected for leaks again.

If the cup plugs continue to leak after installing the sealer tabs, new cup plugs should be installed as follows:

Lower the coolant level so there is no coolant in the cylinder heads.
Remove the cup plugs and clean the bores.
Apply Primer N (LOCTITE product number 7649) to the new cup plug.
Apply LOCTITE 620 adhesive to the cup plug bore in the cylinder head. By applying to the separate substrates you avoid any cross contamination of adhesive and accelerator. This will also prevent any potential pre-curing of adhesive that is applied to an activated surface. The vehicle should be allowed to sit for a minimum of 1 hour prior to refilling and testing vehicle.
Note: The LOCTITE products listed in this PI do not have a GMSPO part number. If a dealer has a question about a LOCTITE product, please call LOCTITE at 1-800-LOCTITE or visit the LOCTITE website at

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True Custom Performance Tuning