Have the sys pressure tested only way to find a leak. These vehicles have cylinder head porosity cracks that are hard to see. The coolant has to go somewhere, if it's internal it might be a leak that is very small and hard to see. Here is some info: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. 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.
I've replaced alot of heads for this problem, pressure test it and check for leaks, it's gonna be internal or external. Post back with any other questions.
Wednesday, January 7th, 2009 AT 10:23 AM