I am a service center owner and technician of over 40 years in SC. Recently, a 2003 Camry LE w/ 70,000 miles came into my shop with a coolant leak. I consulted this forum and others to find proof of the same instance in the Toyota Camry. I write this in response to some posts I read on this site. This is to be informative for those in similar situations.
To do the exam, we pressurized the cooling system and put the car up on the lift. We immediately noticed coolant leaking from underneath the plastic INT intake Manifold in the rear of the engine. I also noticed a Large piece of foam rubber between the Intake Manifold and the Engine Block and Head. This was blocking our view of the leak. We could only see that the leak was behind the foam piece. The only option to discover the source of this leak was to remove the plastic intake manifold, which I did. After this was removed, it became obvious that coolant had been leaking a minor amount for quite some time due to build up between the cylinder head and block.
The only option left is to remove the head, which requires an exstensive disassembly (R and R cylinder head). After Loosening the bolts in sequence, I notice the head bolts in the back of the engine are loose. From my experience in the field, I can confidently conclude that this only means one of two things: The bolts were left loose at the factory, or the Bolts are stripped. ( I commonly have seen stripped bolts in the Aluminum Cadillac North Star Block discovered through leaking coolant.)
Next, I removed the head and sure enough, one bolt came out with aluminum in the thread...thus indicating a stripped bolt.
MY THEORY: The placement of the (insulation) foam rubber piece between the Intake Manifold and the engine block created an uneven dispersion of heat, creating "metal fatigue" in the aluminum block allowing the headbolt to strip.
If Toyota had out an Aluminum Manifold instead of Plastic, there would have been no need to insulate (w/ foam piece), thus eliminating the probem.
The only solution to this problem is to unforunately replace the engine. The cost to repair it otherwise would be substantial. This is an engine defect and we WILL be seeing more of this.