coolant expansion tank question
 

I am wondering if I misunderstand something about the coolant hoses.
I have an LQ9 6.0l in my '70 Impala, I am using the stock Impala radiator.
~Does the radiator need a pressurized cap?
~The steam hose from the heads has to enter the rad "below" the cap, right?
~There is then a hose going from the rad "above" the cap to the expansion tank, right?
~Does the expansion tank need a pressurized cap also?
~What pressure rating should the caps be?
~Because one of the heater hoses is connected with a T to the bottom of the expansion tank, what prevents the pressurized coolant from the heater hose from going into the expansion tank and filling it?

~Does the radiator need a pressurized cap?

Yes

~The steam hose from the heads has to enter the rad "below" the cap, right?

According to the book "yes", but many people T it into the heater return host or tap the top of the water pump and run it there. Some people cap it off completely, but I don't like that. I'm running mine to the top of the water pump.

~There is then a hose going from the rad "above" the cap to the expansion tank, right?

The hose above the cap on your '70 radiator goes to an overflow bottle. The difference between an overflow bottle and an expansion tank is the overflow bottle isn't pressurized and the expansion tank is. Expansion tanks are typically used when the radiator is lower than the engine.

~Does the expansion tank need a pressurized cap also?

If you ran an expansion tank, it would. But you're going to run an overflow bottle, which is vented to atmosphere.

~What pressure rating should the caps be?

18psi is what the LS1's run stock. The LSx's like to run hot, so you want to run a cap somewhere up there so you aren't boiling over in traffic. A 16psi cap should work fine and you can get one at AutoZone, etc to fit your radiator.

~Because one of the heater hoses is connected with a T to the bottom of the expansion tank, what prevents the pressurized coolant from the heater hose from going into the expansion tank and filling it?

You won't run an expansion tank or the T, just an overflow bottle. The overflow bottle will have one hose feeding off the bottom of it, going to the radiator neck.

Thanks a lot for these infos, I did not know those engines could run without the expansion tank and T in the heater hose, this is easier like that!
What size should the overflow bottle be?

Mine's about 2 quarts.