so i know my AST is plumbed "wrong" (i replaced the stock AST, and that's how that thing was routed then). question is, how should i run the lower hose, off the AST, into the radiator? i read 4 threads, got 4 different answers.

also, i have .9 pressure caps, both brand new. another case of many answers...from reading up, it should be no spring on the AST, and a 1.1 bar for the main filler neck? what's ideal?
and please, don't laugh at the filters.

 

The lower hose runs down to the radiator nipple for it.

The top most hose runs to the coolant overflow tank.

The middle hose runs from the coolant filler neck.

 

yep. but aftermarket full aluminum radiator with no nipple. so how should i go about attaching the bottom AST hose?

any other hoses nearby i can run a T to? i want as little failure points as possible in the cooling system...thanks.

 

It looks like you have the Dr. Frankenstein equivalent of the AST-delete modification, but with an AST. I'm amazed that it works. If it does work, I would use a flat cap on the main filler neck and keep a 0.9 bar pressure relief cap on the AST only. (Since the main filler neck has no nipple of its own, using a pressure cap there isn't really appropriate.

With your current radiator having no bottom nipple, you might want to do the AST-delete modification the right way. (Cap the existing nipple located below the current filler neck. Replace your current filler neck with a new 2nd gen RX7 filler neck (one with a nipple) and connect that new nipple to the overflow tank. Use a 0.9 bar cap on the new filler neck. Remove the AST.

 

Boy, lot to look at in that picture .

First, with a normal AST set up, you have a flat cap on the thermostat housing, a hose running from the thermostat housing to the side of the AST, and a hose running from the bottom of the AST to the bottom of the radiator. The AST has the spring cap.

Since you don't have the radiator nipple it would be a huge pain to try and make that work and it's just not worth it. Get the FC cap assembly and a new O-ring that goes between the cap pedestal and the thermostat housing. You can either buy the Mazda part (about $40 or so from Ray Crowe) or get the Banzai Racing part that's aluminum.

With that new cap neck, you will cap off the nipple on the thermostat housing that currently goes to the AST. The hose that goes to the overflow tank hooks to the new cap neck. Spring cap on the new cap neck. Good to go.

Next you REALLY need to get an intercooler duct NOW. Without that duct it's functionally like running with no intercooler, you can get to dangerous intake air temps very easily. That coupled with the intake being so far back and not getting good clean air is a time bomb.

Dale

 

i purchased the ast, as the one in the car was destroyed, and leaking from the cap once the car warmed up. wanted to keep it "stock", but if a delete is a better option, delete it i will do..

this setup really doesn't work. i am losing water somewhere. water loss doesn't appear to be from the exhaust. no drips i've found. i may not have it fully burped/bled out of air to date.

my overflow tank is not sealed at the filler cap. i had to replace the neck tube. i see no leaks there. it is sealed as expected everywhere else.

front was wrecked. so in due time, i've realized i will never get a stock airbox back into this thing. i also can't run a factory passenger side headlight. outside of that, everything seems to have
been pulled back to where i can somewhat work with it. the battery tray absolutely sucks.




that is where the intercooler sits in stock format at least, correct? i see the plastic ductwork that should be there (looking at images). of all the extra parts i took out of that front end, i didn't remove anything that looked like that. i'll go source one, or fabricate something. thanks.

i actually am going to run a hose thru one of the fixed headlight openings to that intercooler as well. i figure that will direct some cold air fed to it directly.

i'm also not against putting a couple of extra holes thru the front bumper, if that can help with cooling at all.


thank you for all information.

 

this might sound dumb...but if i have a nipple 1 inch under the filler neck, why would i cap that off, then install a filler neck with a nipple? is it taller in height, or serves another purpose?

i purchased a new .9 bar filler cap from japan...now i'm learning it's not really useful in that location. the ast came with a new .9 bar cap, so that's in play as well. both original caps on the car when i save it, basically sucked, so they had to go. both of them were also springed. 1 stant (garbage), and the filler neck had a no name 1.3 bar cap, iirc...

 

just get the stock ducting.

 

A pressure cap has an upper seal and a lower seal. The lower seal is sprung and opens when pressure limit is exceeded, allowing coolant or air to pass the lower seal. Normally, the cap is on a neck with a nipple serving the space between the upper and lower seals, so the coolant or air that gets past the lower seal is stopped by the cap's upper seal but can flow out the nipple to the overflow tank. The nipple located 1 inch under the filler neck is the wrong place (if you are modifying the system to eliminate the AST). It is below the cap's lower seal rather than between the cap's upper and lower seals. When the AST is eliminated from the RX7's system, you need to replicate the AST's pressure cap, neck and nipple arrangement in another location -- the new 2nd gen. filler neck, with a nipple and a pressure cap does this.




Here is a useful explanation of how a pressure cap works, and why the nipple to the overflow tank has to be located between the cap's upper and lower seals:
https://professionalawesome.com/how-...nd-race-ready/

 

that...make sense. thank you. so a stock FC 1988 - 1991 rx7 filler neck will work? or do i stick with a brand new neck?

everything's been new for the most part so far. just curious more than anything.


oh, and i highly doubt stock anything in front of the engine pulleys, will work on this car anymore. no point in a stock intercooler duct...car didn't have one when i got it, so that's all new news to me.

but, i can fabricate a duct for the intercooler.

this car ate a tree.

 

Good luck getting that straightened out.

Your current filler neck and the AST will not be used. The AST delete modification uses the nippled filler neck from a 1986-1988 FC RX7 to replace the stock filler neck. If you find a used FC neck, just be sure to replace the O ring under the current filler neck with a new one and use a 0.9 bar pressure cap on it.

Or, order an AST delete "kit" (FC neck, cap, O ring, etc., whatever you need) from Ray Crowe.

Or, you can order the deluxe billet version of the nippled filler neck from Banzai Racing, designed to be a direct replacement for the 86-88 FC RX-7 plastic filler neck. It comes with stainless bolts and an O ring, but a pressure cap is extra.

 

thank you. i'll check all the options.

car drives straight, so that's good. i hit some metal on the driver's side with a full right turn, so there's some more banging out still to do.

but yep. where i am now, not much else will fit in without cutting parts up. driver's fender front bolt hole wasn't even close. the secret? well utilized zip ties.

 

thank you all again. grabbed the banzai replacement since it's aluminum. cooling system now seems to be working well, drove the car 25 miles yesterday, only had to add a couple of ounces of water after it cooled down.

the car is still "burping" out the air in the system, i'm sure.



where can i source the duct? only see a RHD option on eBay currently.

 

That duct should be a piece of cake to find used. No difference JDM or US, but the later JDM cars did have a different duct as they revised the front end. Any you find in the US will most likely be a US part.

Dale