WaLieN

Well, I recently installed a Greddy SMIC. The place where the AST bracket is located is lower than the stock IC's bracket. This causes the AST to sit a little lower (~2"). Could this possibly effect the level of the coolant that I see in my coolant filler neck? Lately, I have noticed that if I fill it up to the top, it'll eventually end up back to the same position again. I did notice that it was puking a little coolant out of my overflow tank after filling the coolant to the top rim at the coolant filler neck (I didn't fill it at the overflow tank). Also, my overflow tank is actually alittle bit overfilled (far above the "F" mark on the dipstick). One would think this is a blown o-ring, but I never get a low coolant light after a few weeks of driving.

I am thinking that the height of the AST location in relation to the coolant filler neck can cause this to happen. I have seen a few people with the Greddy SMIC relocate their ASTs to a higher location (equal or above that of the filler neck cap). From the pics below, you'll notice that the Greddy SMIC causes the AST to sit way below the stock location, far below that of the coolant filler neck.

Heisenberg

iTrader: (3)

I am gonna take a guess at this and sombody can correct me if im wrong. The point of the ast is to get the air out of the cooling system. In order to do this it needs to be at the highest point of the system. From my understanding, the proper way to fill the cooling system is to open both caps and fill the system from the filler neck on the motor. When you do this the air is able to escape from the ast. If you have the ast sitting lower than the filler neck you wouldnt be able to put as much coolant in, if you have both caps open.

adam c

iTrader: (2)

Just make a little bracket, and raise it back to the same level it was at. That should solve any potential problem.

WaLieN

Yes, that is what I had planned. I just don't understand why Greddy made the AST bracket so low.

jic

iTrader: (1)

i have the exact same problem as you. no coolant leak anywhere but the coolant seems to go somewhere everytime i check it. i have a greddy smic and notice it sits much lower than the stock position. ill try to relocate it and see what happens. anyone have any good ideas of how to make a bracket to have it sit higher?

WaLieN

Have a rectangular piece of metal with a hole along the middle so that you can adjust the height as you please.

Kento

I think for the same reason that I wonder how they can deem a piece of sheetmetal with tabs and a square piece of thick rubber (which is actually intended for the IC to rest on top of on the crossmember) as "ducting".
I have the Tri-Point AST which sits higher, so I haven't had this problem with disappearing coolant.

WaLieN

Good point, Kento. The coolant doesn't really disappear, the overflow tank just leaks out coolant when I fill the coolant filler neck to the brim.

Retserof

iTrader: (1)

If I recall, the stock AST is lower than the filler neck and other parts of the cooling system, but is higher than the bottom tank of the radiator.

It is more likely that the problem is due to a bad AST pressure cap or a kink or an air leak in the hose from the AST to the overflow tank. The coolant can't be fully recovered from the overflow tank if the cap or hose aren't OK. The coolant level at the filler neck drops and the overflow tank eventually dribbles out some coolant.

DamonB

Yes on both counts. The height of the AST has nothing to do with your problem.

If the overflow is getting too full that can only happen due to a problem either with the pressure cap or the vent line. The coolant level is going down and the overflow is overflowing because the coolant is being pushed into the tank when the engine is hot, but it's not being recovered back into the system as it cools. This leaves the coolant level in the thermostat housing slightly low and the overflow overly full.

When topping up the system fill the AST and cap it first since its cap is lower than the filler neck. Once the AST is full and capped then top up the filler neck. The coolant level will stay just below the top of the filler neck if the caps and hose from the AST neck to the overflow tank are good.

Gamezilla

Mine does the same crap. I have an aluminum AST thats been moved that sits a tad lower than stock position. Still sits high in the engine bay. If I take the cap off the filler neck the coolant will slowely drop and disapear, but if I fill it up it just spits it out the overflow. I get a solid 83C everywhere I drive. Highest I ever get is 85 after some spirited driving. If you arent having cooling issues I wouldnt worry about it.

Julian

iTrader: (14)

The function of the AST is to be the high point for air to migrate to. I mounted my AST with a piece of aluminum square tubing such that the discharge height was same as stock.

jic

iTrader: (1)

hey julian..i was wondering where you got that cf duct for the greddy smic
ive been running my greddy smic with the stock duct for a while..and i dont think thats a good idea

WaLieN

The AST cap and coolant filler cap have been replaced recently (<5k miles) w/ OE parts. I also inspected them to see if they have any warped seals, all checked out fine. Also, that is the way I tried filling it last time. Is there something that I may be overlooking?

DamonB

Must be. Just think about this for a second. The cap on the AST is the gateway to the line which goes to the overflow and that cap is set to a certain pressure. Where the AST is mounted has nothing to do with coolant getting into or out of the overflow.

When the coolant gets hot it expands and when pressure exceeds the rating of the cap coolant can proceed out the cap and through the line to the overflow. After shutdown and the coolant begins to cool off the coolant volume inside the engine "shrinks". This creates a vacuum that sucks the coolant back out of the overflow and into the AST. If there is even a small leak in ANY coolant hose or cap this will act as a vacuum leak and so when the engine cools it won't refill as it will suck air rather than coolant.

Check the caps and their necks again. Check the fit of all the hoses on the AST and engine. Check the fit of the overflow hose to the neck and the overflow tank. A tiny leak at any of these places will cause your problem.

The height of the AST cannot cause the problem you have.

DamonB

No it's not. The AST is not the highest point in the system, the filler neck is.

If you tried to make the AST the highest point in the system you'd have to cut a hole in the hood.

DaveW

Absolute correct! Check those hoses and caps!

WaLieN

I was under this impression as well, thanks for the advice Damon. I took a look at the AST coolant lines last night and found that the one leading to the radiator was somewhat kinked due to the lower mounting position of the Greddy SMIC. I rerouted it (causing a huge mess along the way) and hopefully that might have fixed it. I'll keep you guys updated.

DaveW

I doubt that this hose could cause your problem (unless it was completely shut off) of low coolant in the engine and excess coolant in the O-F tank - it would just restrict the flow through the AST to the radiator. The coolant would still be sucked back from the O-F tank, regardless.

KevinK2

This means one of these is true:

A) those 3 10mm hoses are not connected properly

B) you have a proper sprung cap, leaking internally at the ast << best bet

C) you have the wrong cap at the ast, with no coil spring.

Retserof

iTrader: (1)

Actually, if your AST is mounted lower than stock, it would have a slightly easier time recovering coolant from the overflow tank as the system cools.

Most likely the problem is an AST that blows but won't suck, due to a bad cap or a small air leak somewhere between the body of the AST and the bottom of the pickup tube in the overflow tank.