Help!- New Valve Job and Boom the radiator blow up

[LVLT FIXIT]

2 weeks ago I pulled the head on my 1995 Camry (224,000 miles) 5Sfe 2.2 4 cyl. for valve seals (cloud of blue smoke every morning) and it was starting to run hot and use some water (8oz. in 100 miles) - did a full upper while I had the head off. Dye checked for cracks, machined the head, did a valve job – no burnt valves, and used the Fel-Pro 9861PT Perma torque Printoseal valve grind gasket set. Carefully cleaned the block with a razor blade scraper. Then when over it lightly using small circular pattern with 1500 grit sand paper and mineral spirits using a 1”sq. x 8” long cobalt lathe bit as a backing for the sand paper bridging over all holes and cylinders. Block was very flat, no burrs or corrosion. Cleaned all bolt holes with a .38 gun brush, rinsed, blew out and vacuumed them with an air vacuum. Block and head got a full wipe down until cloth was clean using MEK. Sprayed the head gasket with a light coat of Copper Coat and installed the head using new bolts and washer. Torque to 36 ft. lbs. in 3 steps (15,30,36 lbs.) Used a homemade protractor to final torque to 90 degrees in 3 steps of 30, 60, and 90 degrees. All threads and washers where oiled with 10w40 engine oil and hand wiped prior to install. All block threads had an oiled bolt run in to bottom prior to head install after cleaning. Changed oil, and filled the radiator with a gallon of antifreeze (DEX-Cool), the balance with distilled water approximately 5/8 gallon. Purged the hoses by squeezing them several times. Filled to within ½” of radiator neck, and started the car, it ran very smooth. I then topped it off after about 4 minutes run time and put the cap on.
Then the trouble started. The radiator split wide open across the top and a leak at the tank to core crimp seam after 6-8 minutes idle time. Blew steam and water sky high. Apparently I have compression in the cooling system. Currently trying to figure out why this happened.
After letting it cool down I A/C duct taped the top tank, added water and re-started the car with the radiator cap off. Idled fine, no overheating, no obvious bubbles in the radiator. Raised the rpm to 1300-1500 and the temp gauge started to rise. Fans cycle every time the a/c does and the fan cycles on and off without the a/c on above 1200 rpm. I don’t think the fans ever came on before it blew up and it did not seem to be overheating. It all happened so fast, I don’t think the engine had time to come to full operate temp. The car ran approximately 6-9 minutes before the radiator blew up. I then removed the thermostat and checked it in a pan of boiling water on the stove. It worked fine –started to open just before the water boiled and was wide open at the boiling point. I put it back together without the thermostat to check the water flow in the radiator, idled it 12-15 minutes all ok temp normal. Seem to be ok. Put the cap back on and within 2 minutes the temp was rising, at 4 minutes it blew the tape off the radiator. A/C duct tape will hold 30+ pounds of pressure.
I didn’t know where to go next, but that kind of pressure in the cooling system sure looks like a bad head gasket, so I begrudgingly pulled the head. I check the torque at tear down and it was good. Head bolts were new and are within .010 of each other in length. I see no sign of a leaking head gasket. Beautiful text book seal everywhere. Only has 30 minutes run time so not enough time to leave a good water track. Took the head and gasket back to the machine shop to let them have a look. The machine shop owner is a top certified 40 year mechanic/machinist with race car experience in track, drag racing and salt flats, want mention his name here. He rechecked the head for cracks with dye check and found nothing. He called friends and 3 more looked at it – nothing. Rechecked flatness – it was good and the surface finish is very good too. Head gasket has a nice even compressed thickness of .057 at 6 locations around all cylinders.
I brought the head home and duct taped the machined face to seal the water holes, set it on end and filled it with water. 2 hours and no sign of seeping. Then I pressurized the water in the water jacket to 30 psi –nothing again. So then I dumped the water out and set it chambers up level, filled them with water and pressurized the water jacket to 30 psi. Not a single bubble. So I’m convinced the head is not cracked.
Water pump bearing is tight with no end or side play and rotates smooth. I can see the impeller from the thermostat side and there are no missing or damaged fins. It has about .250 to .3125 clearance between the blades and the rear of the housing. The shaft is flush on both ends with the gear and the impeller. Tried to turn the gear and hold the impeller ( hard to do) but could not get any play or slippage of impeller on shaft.
Radiator is 5 years old and very clean inside, same on the 13-15 lbs cap. This will be my 3 nd radiator in this car. They cracked at the top of the tank and leaked but did not explode like this one on 6-8 minutes run time.
I’m lost!!! How can you get that kind of pressure, to blow up the radiator in 6-8 run time and not be able to find a crack in the head or signs of a blown head gasket? I have checked everything I can think of.
Conclusion:
Was it the Copper coat on the head gasket that washed out?
Did the thermostat stick at start up? The engine was open but covered for 3 weeks for the repair.
Some strange design causes a giant air bubble in the head. It did act like it suddenly got water in the head that turn into a steam explosion. The car was still on jacks i.e. front high.
Is it possible to get an air lock anywhere in the 5Sfe engine?
Crack in a cylinder wall? Don’t see one, but no way to check in the car.
Was the radiator old hard and brittle and maybe it just was time to go?
Could I just be getting old a stupid?
Any comments or suggestions would really be helpful and appreciated as I am lost. 48 years messing with cars, even had a cylinder head svc for race cars only before going into jet engine mechanics.
Thanks

[SexieWASD]

The only time that I have seen a radiator behave like you describe is when a stuck thermostat snapped open and flooded an overheating dry block. I would replace the radiator, cap and thermostat (just because they are cheap enough) and give it another go, this time with a pressure gauge on the radiator. It definitely should have taken more that a gallon of coolant to fill both the block and radiator, but even still the 5s's are really easy to bleed. I haven't had a problem yet doing it as you described on these cars. I don't jack mine, I use a lift, so maybe that was the difference? I would leave the copper coat off, just because. The fel-pro gaskets don't really need it anyways.

Even with a full on huge leak of compression into the cooling system I haven't seen it blow a radiator, the cap can usually deal with it ok.

[Mister_Perkins]

Your head gasket will never leak that much compression into your water jacket unless you have a giant hole on the cylinder wall To let all the compression into the water jacket. In that case your motor would more than likely seize on the giant hole. If it did run, your cylinder would fill full of coolant, so when you would pull a spark plug the excess coolant would shoot out of the spark plug hole. Highly Unlikely / virtually impossible without being seized

I would check / replace the cap and also pressure check the radiator. If you think your getting compression into your coolant do a hydrocarbon test. Easy

[JohnGD]

I'd suspect the radiator cap first. The cap only holds 0.9 bar (~13 psi), so it should be letting off the pressure. Some people see bubbling in the reservoir tank when a head gasket blew.

As for the block, with out a magnaflux you won't know if there is a crack in the block. But you should see bubbling in the reservoir tank if there is.

[peshwa]

What was the result of a cylinder leak down test? And a compression test? I usually use a block tester (from my local auto store) to check for exhaust gases in coolant. What color was the remaining coolant when the radiator blew up?

[LVLT FIXIT]

Put the head back on today. Still don’t know what happened. I will finish putting it back together tomorrow.
Dye checked the head again, found no cracks. Pressure tested head with water in the jackets and 30 psi – no sign of leak. Filled the combustion chamber level full and pressurize the water jack with 30 psi – no sign of a crack. Pulled the pump off and pressurized the block – this was a pain. Use some soapy water spray on the cylinder walls and top of block no sign on a leak. Put the pistons 2 each at a time up and soaped around top of each for air bubbles –nothing. The top of the block was seal off as where the heads when I checked them with the 30 psi.
This time around it will have a new radiator (due to blowing up the last one) and cap, thermostat, and another new head gasket, new head bolts again –this time without the Copper Coat on the head gasket.
Note: SexieWASD said 1 gallon coolant was not enough – In the original post note I used 1 gallon of antifreeze and 5/8 gallon of distilled water for a total of 1 5/8 gallon in the radiator/engine = very near the limit for a 5Sfe engine. Note: Mister Perkins – there is no tank left on the radiator, it blew apart 8 minutes after start up.
Thanks everyone for the help.