GMC Yukon XL 2000–2006

▸Known issuesCastech cylinder head porosity crack (gradual coolant loss)1

1. Manufacturer communication2001–2006 GMC YUKON XL DENALI ・ 2024-03-19

   Internal Coolant Leak from Cylinder Head Location

   1. 1Fault

      • Leak
      • Some vehicles may experience a gradual coolant loss over time.
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   2. 2Finding the cause

      Possible causes

      • A very low percentage of cylinder heads manufactured with an embossed Castech logo may develop a porosity crack in a very specific area.

      Steps to confirm (in the document’s order)

      1. Check whether the head is a Castech casting by looking for the casting logo on top of the intake port, under the rocker arm support rail and in the spring deck cavity portion of the cylinder head.
      2. If the head is a Castech casting, inspect the area around the five oil drain holes for witness marks indicating coolant seepage over time.
      3. The crack can be in any of the five cylinder head oil drains and shows as a clean or shiny area on an otherwise stained surface.
      4. Pressurizing the cooling system at this time may reveal coolant, air, or a combination weeping in the described area.
      ↓→

   3. 3Correction

      Repair

      • If inspection reveals evidence of coolant witness marks, replace the entire cylinder head assembly.

      Caution

      • If the cylinder heads are not a Castech casting, follow normal diagnostic procedures in SI to determine the cause of the coolant loss.
      • If no evidence of coolant loss is found on inspection of Castech casting cylinder heads, follow normal diagnostic procedures in SI to determine the cause of the coolant loss.
   Read the sentences of the record

   From the manufacturer’s document

   • Applies to：Applies to 2001-2006 GMC Envoy, Jimmy, Sierra and Yukon models, among other listed GM models, with the 4.8L, 5.3L or 5.7L VORTEC GEN III, GEN IV V8 engine.
   • Condition：Some vehicles may experience a gradual coolant loss over time.
   • Cause：A very low percentage of cylinder heads manufactured with an embossed Castech logo may develop a porosity crack in a very specific area.
   • Confirm：Check whether the head is a Castech casting by looking for the casting logo on top of the intake port, under the rocker arm support rail and in the spring deck cavity portion of the cylinder head.
   • Confirm：If the head is a Castech casting, inspect the area around the five oil drain holes for witness marks indicating coolant seepage over time.
   • Confirm：The crack can be in any of the five cylinder head oil drains and shows as a clean or shiny area on an otherwise stained surface.
   • Confirm：Pressurizing the cooling system at this time may reveal coolant, air, or a combination weeping in the described area.
   • Repair：If inspection reveals evidence of coolant witness marks, replace the entire cylinder head assembly.
   • Caution：If the cylinder heads are not a Castech casting, follow normal diagnostic procedures in SI to determine the cause of the coolant loss.
   • Caution：If no evidence of coolant loss is found on inspection of Castech casting cylinder heads, follow normal diagnostic procedures in SI to determine the cause of the coolant loss.

   Open the manufacturer’s document (PDF) ↗ The points above were read from this document.

   Remedy

   This bulletin advises the technician of possible location of an internal coolant leak from a specific cylinder head and location.