ok...i do not have an ast. and i recently replaced my filler cap. now the cap is from an ast, since it has to be pressurized. so why is coolant still pissing outta the cap when the car starts to warm up? does that seal on the filler neck ever go bad???

 

ttt

 

you cannot use the ast cap on your filler neck. Switch it out for a radiator cap with the proper psi. Because the ast cap deos not have a spring, your coolant continues to flow into your overflow tank, which then overfills and dumps your coolant out.

 

ive had the ast cap on for over a year with no problems. it only recently started pouring out of it

 

i thought it was the other way around
the ast has a spring while the radiator filler cap doesnt

 

yeah jic you are right. all the write ups that tell you how to eliminate the ast tell you to put that cap on the filler neck

 

flyboyjudge, it's not quite that simple. The pressure-releif cap (marked "0.9bar / 13psi") will vent coolant in order to keep the pressure near 0.9 bar.

Notice that the AST has a line running from the top (near the cap) to the plastic coolant overflow tank. Since your filler neck doesn't have this overflow line, coolant will spill onto the ground when your system pressure reaches 13psi.



This is why people use the FC filler neck, because it has an overflow line built into it.

-s-

 

but it vents enough coolant to where the add coolant buzzer comes on. its just sort of strange that it just started happening outta the blue. thanks for the reply tho

 

How long have you had the AST removed? Did the car always spew so much coolant?

-s-

 

the ast has been removed for over a year...well over a year. no it didnt spew any. recently i installed a greddy two row fmic and had to bleed the whole system and im wondering if the seal on the filler neck itself may have wore out from having the cap on and off soo much recently. the car has over 140k on the clock. maybe 40k on a reman engine. that was my question was if that seal ever goes bad.

 

The seal can go bad, but I think your car's running hotter because of your FMIC.

-s-

 

my temps are mid 80s celcius at all times

 

To eliminate the AST properly, you need to install an FC neck with the overflow nipple which will allow the system to overflow to the resevior. You most likely have lots off air trapped in your coolant system as a result of emptying it for the FMIC install. The seal and the thermostat on the cap can both go bad, replace it with a new one. You still need to burp the coolant system, air will create hotspots which can lead to coolant seal failure.