Originally Posted by remauto1100
What year is your 5.3L ? Any specific target years for the donor engine?
Be aware of this TSB for truck engines with Castech heads if you plan on using stock heads. Not all have the problem, but I'm about to replace heads on a friend's who does.
GM TSB# 06-06-01-019B (came out 06-12-2007)
Subject: Information on Gradual Coolant Loss Over Time With NO EVIDENCE OF LEAK FOUND
2004-2006 Buic Rainier
2001-2006 Cadillac Escalade
2001-2006 Chevrolet Avalanche, Blazer, Silverado, Suburban, Tahoe, and Trailblazer
2001-2006 GMC Envoy, Jimmy, Sierra, and Yukon
2001-2005 Oldsmobile Bravada
2005-2006 SAAB 9-7X
With 4.8L or 5.3L VORTEC GenII, GenIV; V8 engine (VIN's V,T,M,M,Z --RPO's LR4, LM7, LH6, L33, and L59
Some vehicles may experience a gradual coolant loss over time. A very low percentage of cylinder head(s) manufactured with an embossed Castech logo may develop a porosity crack in a very specific area.
Inspect the cylinder head assembly to determine if the casting was manufactured by Castech. This can be accomplished by inspecting for their casting logo located on top of the intake port, under the rocker arm support rail and in the spring deck cavity portion of the cylinder head.
Important: If the cylinder head(s) are Not a Castech casting, follow normal diagnostic procedures in SI to determine the cause of the coolant loss.
Refer to the following illustrations on how to identify Castech casting and/or the very specific areas of the cylinder head(s) for a coolant leak from porosity.
If the cylinder head(s) is a Castech casting (1), inspect the area around the five oil drain holes for witness marks indicating coolant seepage over time (2).
Important: If No evidence of coolant loss is found on inspection of Castech casting cylinder head(s), follow normal diagnostic procedures in SI to determine the cause of the coolant loss.
The crack location can be found in any of the five cylinder head(s) oil drains. This can be seen as a clean or shiny area, on an otherwise stained surface (1). Pressurizing the cooling system at this time may reveal coolant, air, or a combination, weeping in the described area. If inspection reveals evidence of coolant witness marks (1), replace the entire cylinder head(s) assembly.
GM bulletins are intended for use by professional technicians, NOT a "do-it-yourselfer". They are written to inform these technicians of conditions that may occur on some vehicles, or to provide information that could assist in the proper service of a vehicle. Properly trained technicians have the equipment, tools, safety instructions, and know-how to do a job properly and safely. If a condition is described, DO NOT assume that the bulletin applies to your vehicle, or that your vehicle will have that condition. See your GM dealer for information on whether your vehicle may benefit from the information.