Overheating Trouble!

[07Burb]

The short story is my 5.3 gen 4 won’t stop overheating.
 

The long story is all my trouble started when the engine ate an AFM lifter and the camshaft. I deleted the AFM through a cam, cam sprocket and chain, lifters, valley plate, and oil pump replacement along with an ECM tune.

 

After putting it all together it ran fine for an entire month. Then the engine burned white smoke on two seperate occasions. A week later, it overheated and continues to do so still. 
 

I have replaced the thermostat, water pump, expansion tank, and radiator. I have pressure tested the system (held pressure over night) including the tank cap. I have tested for exhaust products from cold through all heated up on two occasions and the test was negative both times. I boiled both the new and old thermostats and both opened like normal and similarly. I have verified coolant flow and that all hoses are installed correctly. I “burp” it by following the 30 second intervals of 3000 rpm process. 
 

It will run for an hour plus in my garage at idle with the cap on and the cap off. The overheating happens when the engine is under load. It seems like there is pressurized air being introduced into the system causing it to have air pockets and boil over which then blows a bunch of coolant out of the expansion tank pressure relief. 

 

My dad is a mechanic and I did all the work with his help, we are both stumped. I know the first suggestion will be a head gasket but wouldn’t the pressure test and exhaust product test rule that out? Any thoughts?

[Mikebtte]

When it is overheating have you checked temperature drop acrossed the radiator? Make sure it is not clogged and cooling.

[07Burb]

Yes there is a measured temperature difference (with a temp gun) from the upper to the lower hose. I even installed a clear hose between the upper hose and the radiator to verify flow. It is pumping coolant and obvious when the thermostat opens up. 

[07Burb]

Both the upper and lower hoses get really hard like they are excessively pressurized when up to temp. 

[txab]

Sounds like head gaskets. you can get test strips that should determine if exhaust gas is present in the coolant. And yes you can have a pressure test hold and still have a head gasket leaking. Cylinder pressure is greatly higher than cooling system test

[07Burb]

I twice performed the test with the block tester where the blue fluid is supposed to turn yellow if there are exhaust products in the coolant. Negative results both times.  

[sefiroxx]

Compression pressure is 10x the designed water pressure.

Pull the plugs and see if one is steam cleaned. Do one at a time and do compression test.

[mjm-1957]

Were the correct head gaskets used? GM or aftermarket? When the strike was still going on we could not get GM head gaskets and attempted to use aftermarket ones and some were missing steam holes and had no holes where the original ones did. Something to check.