lowered AST won't allow me get coolant full
 

Due to a new intercooler, I had to re-locate my AST so now it sits about 4-inches lower than stock.

I took the opportunity to flush and replace the coolant (70% distilled water & 30% G-05 coolant), but now I can't get the coolant full when adding from the water neck.

I first filled the AST, capped it (I run a 16-lb. cap), and then proceeded to fill from the water neck, but it would not fill, and eventually the coolant overflow tank, overflowed.

Thinking I had a bad AST cap, I got a new one, and I still have the same problem.

I doubled-checked all hoses, pressure tested the system, and all is good.

Could the lowered AST cause this problem ?

As in, there is now too much water pressure due to the lowered AST, that the AST's pressure-cap won't seal to the overflow tank.

I read this thread, and it shouldn't:

https://www.rx7club.com/showthread.p...ght=AST+height

I've also included pics of where the AST was before and AFTER the relocation (below the intercoolers output).

Thanks in advance,
:-) neil

someone can chime in if im wrong, but isnt the ast supposed to be equal to or higher than the filler neck in the cooling system? ive always thought this but then again i may be wrong.

I just have the pressure cap of the AST removed in the second picture. It is not run without it.

According to the link I posted above, it shouldn't matter if the AST is lower.

Thanks,
:-) neil

The AST does have a pressure cap the filler neck does not have a pressure cap. And i believe the AST needs to be the highest in the system for it to bleed out air.

interesting, that thread was rather informative. sorry i couldnt answer your problem but i learned something!

The mounting height of the AST is not your problem. From your description, I suspect that there is a clog in the hose that leads from your AST to the overflow tank. Even if the hose holds pressure, there is a plastic connector piece that could be clogged.

FYI - I have the Greddy SMIC and have had no problems with filling coolant/burping system using the mounting position that comes with the IC.

there is something wrong with your pressure cap on the AST. the only time iv had this exact thing happen is when the pressure cap had something in it like dirt or rust flakes in the draw back flap of the pressure cap cleaned out it should be fine. being that you changed caps seems you need to verifie that the cap is actually sealing to the AST itself from he sounds of it. its not because its low just something with the cap if you keep filling at it keeps going into the overflow.

z

^^ ditto. Even if you had the AST under the car, the minimal pressure of the water against the cap from it being low in the system wouldn't cause coolant to back up into the overflow tank. It has to be getting by the radiator cap somehow.

Also, with the AST that low, it really isn't doing a whole heckuva lot. I'd just eliminate it, get the FC filler cap and sell the AST.

Dale

As several posts said above, the height of the AST should not make a significant difference in its function. Even the stock AST location is below the filler cap. Since the AST is fed from the filler cap neck, air will still go to the AST and be purged into the OF tank as the coolant expands. I agree that a higher mounting would make it work a tiny bit better, but it should still work at any height, as long as everything is correct in its function.

Coolant cap and car not keeping coolant / coolant always low
 

I doubled-checked the new cap, and the overflow valve is not spring-loaded closed.

I went to the McParts store, and all of the new same model number caps (Stant #331) are designed this way.

I did find a Stant 16-lb. cap (pn# 11230) that had the overflow valve spring-loaded closed, and all is well again.

The only way to check is to inspect the cap from the side to see if the valve hangs down, and to gently pull on the valve to see if it is spring-loaded closed.

I'm wondering if this should be a "stickie" . . .

Check out the pics.

PS: I also found a 13-lb. cap with the spring-loaded overflow valve.

:-) neil

nice job finding the REAL problem glad we could help.

z

Good thread. Linked to it from the FAQ.

ast needs to be higher than the top of the radiator or it won't bleed the air out properly

I never said my AST is lower than the radiator.

My AST is higher than radiator, but remember stock AST is lower than the water fill neck.

:-) neil

Generally, that might be true, but in the case of the FD, coolant circulates from the top of the fill neck through the AST and then into the bottom of the radiator. So the relative position of the radiator top and the AST is not very important. Any air collected at the fill opening (highest point in the cooling system) will wind up in the AST and be purged to the OF tank as the coolant expands.

Dave

Did the overflow tank fill up when you where driving, or just sitting there while you were trying to fill the engine?

Are you sure you didn't mix up the lines when you reconnected the AST?

Mods, please close/lock this thread.

Thanks,
:-) neil

Dale,

you hit the "nail on the head". With it mounted so low, it wasn't acting as an AST, so no air was being "burped".

In short, I had to re-locate the AST to the same height as the coolant fill neck to make it work properly. At the same level as the top of the radiator, is still too low!

More info here:

https://www.rx7club.com/race-car-tech-103/coolant-not-being-sucked-back-908664/

:-) neil

Thread dredge... I'm having somewhat the same problem, every time I drive I lose a fair bit of coolant, and the only place I can see it coming from is from the overflow tank and it's always wet around where the AST>overflow hose that goes into overflow tank, and the small hole that's beside that on top of tank.

Reasons as to why it's coming out there and I'm losing so much coolant that warrents filling up after every drive, and this is like a 30-45min drive...worrys me a bit.

Just switched to alloy AST (mounted same height as filler cap) and flushed system out. Any help to recitify this would be appreciated.

Also thinking perhaps my coolant seals may be on their way out? Not confirmed at all though other than slight bubbling in WP neck.

Make sure you have the right AST cap as shown above.

Then REPLACE ALL hoses between the AST and the coolant-overflow tank. THIS CONNECTION MUST NOT HAVE ANY LEAKS EITHER UNDER PRESSURE OR UNDER VACUUM.

When the engine is hot, and the AST cap pressure is met, coolant flows INTO the coolant overflow tank. As the engine cools (and assuming the coolant system is airtight), a vacuum is created that draws/sucks back coolant from the overflow tank.

:-) neil

are you still using the 11230? pep boys has it in stock across town.
what size is the generic radiator hose?
I have the AST removed, but I want to replace the hose from the overflow tank all the way to the filler neck with one piece