Symptoms:
Car over heats after 20-30 minutes
Pressure builds very high in the reservoir tank, enough that the release valve opens and causes a 'whistling' sound.
No heat in the cabin.

Vehicle history: No stop leak or any other type products into coolant systems & nothing other than oil into engine. There is no evidence of coolant mixing with oil (I have not removed the valve cover though). The cap of the oil filler had very little milky residue that seemed to be more of condensation. When I drained the coolant there was no evidence of oil on the surface). No other issues until this. Thermostat has been placed correctly into the housing. I do not let the engine run after the 1st signs of large build up in the reservoir & when the gauge starts to climb into the upper 3/4 range + temp reading on my scanner of 235 ish. I also have ordered the GM thermostat and it will arrive on the 30th of Nov. There is an aftermarket Auto Zone one in there now (I did test it in boiling water and it does seem to open & close) but I figured I am so far down the rabbit hole why not order an original t-stat.

Test performed:
Block test - came out negative (color never changed to yellow or brown, stayed dark blue).
Leak down test - there was some loss of compression but all tested tested to the 'moderate/green' indicator on gauge. No other areas can be heard to leak the air.
Vacuumed system with venturi type filler system. System held 25 psi. Refilled system with Dex cool via same vacuum.
Also tried to bleed system by leaving cap off the reservoir.
Disconnected all hoses (lower & upper radiator hoses & heater core hoses) to check for obstruction - none found.
Ran distilled water from top of radiator port and water flowed freely to bottom of radiator exit port.
Started the car from cold with the reservoir cap off to see if there is a sudden pressure release into reservoir - tested negative.
There are NO codes.
Fans turn on (somewhat late in my opinion but they may be set that way. They turn on when the engine is closer to 200-220 degrees
No evidence of coolant in the engine oil or on oil cap.
No bubbling in the reservoir (only vapor/water forms on the top of the canister when pressure begins to exceed the caps maximum).
No stop leak ever introduced into the system.

Replaced:
Water pump
Thermostat
Engine Temp Sensor
Coolant
Reservoir and cap

Is there any other test or procedure I can complete before I make the determination that it is a blown head gasket since it is not really indicating this is the case?

 

I'd check your water temperature manually or with a scan tool. Other than a plugged up radiator or a bad inner lining restriction on the water hose, I'd still go with a bad head gasket.

There is no shame in using Bar's Leak or Alumaseal if the leak is small, but they won't usually stop a large head gasket leak anyhow. Cheaper than doing the head gaskets. They will NOT plug up your radiator, BTW.

 

Thank you - I did do a live scan with my scan tool and was able to see the water temperature from beginning to end (when it started to over heat) if that is what you mean. As soon as I put in the new OE t-stat from GM and if that does not change things I think you will be right - head gasket has failed somewhere.

 

It happens. Particularly if you have lots of miles on the engine. Too, lots of things on vehicles these days are not built well, particularly stuff from Asia, but head gaskets have been leaking ever since I can recall and that's a long, long time.

 

Here is an update. I disconnected the outlet heater core hose while I had the vehicle running. Here is what that looked like (no water from the hose, but coolant spurting from the inlet tube).

Video - 1

 

Was this after you added water or coolant to fill the system?

 

Yes, this is correct.

 

Can you smell any oil or exhaust fumes?

 

None that I can tell.

 

How much longer will it be until your T-Stat is ready to install?