Redoing cooling system. Have a few questions about proper routing.

[bmorecobra]

So I am in the process of making an oil cooler kit for my car and want to finish off the upper half of the coolant system by doing all AN parts up top. Simultaneously while doing this I figured it is a great time to replace the stock expansion tank with a smaller aluminum expansion tank to give me more room under the hood.

Now, I already have the MMR y-block and block fittings and have been using them for a while, but with the stock expansion tank.

My question is about the stock expansion tank. I want to replace it with a smaller one, one that has a filler on top (so I can add fluid just like with the stock expansion tank). Essentially I want it to act/perform just like the stock expansion tank.

Looking at the stock expansion tank it has the bottom outlet which goes to the lower rad hose, the top outlet which I have recirculated into the radiator, and a pressurized cap. Pics for reference:

However as far as I can tell the pressurized cap is not hooked up to/regulates the small top hose at all. Please correct me if I'm wrong!

From the looks of it the pressurized cap if vented would go to the atmosphere. The small hose simply recirculates back into the system when the coolant level becomes high.
Again, if I am completely wrong on this let me know.

This is my plan to emulate what the stock expansion tank does in a smaller package:

http://www.summitracing.com/parts/aaf-all36115

Using the above tank (3/8" NPT on top side, 1/8" NPT overflow vent on filler neck, and 1/2" NPT port on bottom) I would:

-run a barb fitting in the 1/8" NPT filler neck port back into radiator (with a 16 psi radiator cap)
-plug the top side 3/8" NPT port
-run a barb fitting in the bottom 1/2" NPT port back into the lower radiator hose like stock expansion tank

Would that work? Or should I run the barb fitting off the 3/8" top side port back into radiator instead and then plug (or leave open) the 1/8" NPT filler neck port?

Any clarification is much appreciated. Should look much better when finished.

Thank you in advance!

 

[BeanCrusher]

It seems to me that you would run a hose from the filler neck port towards the ground for overheat/overflow, connect the small hose from the radiator to the 3/8 side port and the lower port to the lower radiator hose like you said.

Running the little hose from the radiator to the filler neck port would mean you are applying pressure "above" the radiator cap.

Your description of the lack of relationship between the cap and the small hose port in the stock tank is correct. I believe that the purpose of the tank is not just to allow for expansion, but to also keep air pockets from forming in the engine coolant passages....I'm not sure where I got that idea, or if it is correct....