FikseRxSeven

it sparates the air from the coolant

tampaFD

i got that but why design one in the first place?

GarageBoy

Once air gets trapped, fluid isn't going to move as well.

tampaFD

agreed, but there are alot of people who are having positive results with it removed. what gives?

-=RX-7 KID=-

maybe it has something to do with every one using aftermarket rads? Any one see better results with stock rad?

jspecracer7

The volume of the filler neck is small in comparison to the AST tank. The AST because of it's larger volume can hold/trap more air than just the filler neck alone. Once your cooling system has had the air bubbles removed, the AST tank has no purpose.

FikseRxSeven

does it matter whether i get an s4 or s5 filler neck?

teknics

bla bla its the only rx7 that has an ast..... and was there a radical change in how engines are cooled between 91 and 93? nope, then it's just excess, chop it out.



kevin.

Silver Ninety Three

I usually eliminate them. I have been running without one for 4 years now and no problems. The only reason I see why mazda put it is to help bleed air out of the coolant system after flushing it. Without the ast it is a bit harder to get the air out. Get rid of it for simplicity. Use a2nd gen fillerneck top tha has the nipple on the side. The newer ones are one piece so make sure you get the 2 piece one.

teknics

i figure by 2 piece you mean the s4 aluminum piece? 86-88 = s4 (u have a 2nd gen u know that probably lol)



im asking cuz martin told me and i asked if he needed s4 or s5 cuz im having an s5 neck made in aluminum for my car and if it was an s5 he needed an aluminum one is better then the stock plastic s5 piece. but my s5 is one-piece and i think the s4 is 2 piece and metal so i guess you're referring to that one.



does the s4 neck bolt right up to the 13brew? cuz i know to put an s4 neck on my s5 i need to change out the whole waterpump.



kevin.