supracosworth

AST elimination mod -- Instead of getting the FC radiator neck with the runoff tube, is it possible to drill a hole in the FD's radiator and fit/braze a 6mm runoff ? Has anyone done this before?

I'm not trying to save a few bucks but I've ordered the FC radiator neck using the part number rspecified on the Scuderia site but the item turned up to be the same as the FD. The part no. is right its just that the HK distributor can't get hold of the old item anymore.

Rgds

Michael

supracosworth

Sorry that should read radiator neck.

puma

iTrader: (2)

hmm, i jus bought one two weeks ago...

what was you part number?

supracosworth

As I say, the part number is correct but I'm now relocated to Hong Kong and the dealer here can't get hold of the FC item. I thought I read somewhere on the forum that this could be done but I can't find the thread.

lerch32

iTrader: (6)

What is that part number? I need to order one.

XSTransAm

i was actually wondering the same thing??? is this possible? i cant see any reason why it wouldent work?

supracosworth

The FD's radiator neck appear to be shorter than the FC's but I'm not sure without putting the two side by side. Don't know if the runoff can clear the radiator cap.

spurvo

How in the world does this work? How do you maintain pressure in your system this way? Or are you running Evans with 0 psi? Without a pressure cap of some sort (as I understand it, the AST elimination mod just moves the pressure cap to the filler neck) you will just overflow as soon as things get warm (unless you have Evans, and even then some will come out), right?

Or do you mean to drill a hole in the side of the fillern neck and out your own nipple there? You should be able to do this and use a pressure cap right on the filler neck the car comes with, as there is a seat right there that would interact with a pressure cap.

I'm all confused and stuff!

maxcooper

From spurvo's description, it sounds like there is a seat so it should be possible to add a vent tube to the existing FD filler neck. You would certainly need to use a spring cap in that position, as opposed to the simple cap that normally goes there. Also, some FD filler necks do not have a replaceable cap/neck thing anyway so you can't do the normal elimination with them -- I am not sure if they are all the same in terms of having the lower seat or not.

I suggest learning how a radiator cap works so that you can make your determination about whether some AST removal technique will work or not. Here's the scoop:

1. The pressure cap seals against a seat that is down in the hole a bit. It also seals along the top edge of the cap. The vent tube is connected to the system between the two seals on the filler neck.

2. When the pressure in the cooling system exceeds the cap's spring pressue, the lower seal will break and coolant will flow out the vent tube to the overflow tank. When the venting lowers the pressure down again, the cap will seal up again.

3. The cap also has a lightly-sprung valve (often looks like a button on the bottom middle of the cap) that allows coolant to flow back into the engine. When the engine cools, it will create a vacuum in the cooling system that opens this valve, sucking coolant from the overflow tank back into the engine. It is important to have an air-tight vent tube or this suction action won't work. The vent tube will also vent into the bottom of the overflow tank through a tube (typically) so that it will suck coolant rather than air when it needs to drink some coolant back in.

Now that you know, you'll be able to determine the feasibility of a system change and troubleshoot problems in this area. Understanding is much more valuable than a simple answer. Sorry to sound like an ***, but most people seem to be seeking answers, when I think they would be much better off seeking understanding.

-Max

spurvo

Yes, I notice on the replacement water pump housings I've dealt with in the last two months (water pump and housing replacement, engine replacement) that there isn't a removable filler neck section as there was on the original T-stat housing, so the FC filler neck repop for AST elimination wouldn't work there! So they would have to drill into the filler neck to make this work.

I had just read them as saying you could drill into the "radiator neck", perhaps meaning the upper hose mount on the radiator itself, and that seemed a little hinky to me Maybe supracos meant the filler neck...

Brentis

So Max... When the radiator cap allows coolant into the overflow. How does the coolant ever get back into the radiator? This is a basic question I've been thinking about as I recently installed the AST and seem to be losing a bit of coolant and suspect that this is occuring.

Brentis

I ordered mine from mazdatrix. www.mazdatrix.com

mks

Didn't read this?

Brentis

oops. Thanks for highlighting it for me. Makes a lot of sense. I'm wondering if I am having problems because I used the old pressure cap from the orig FD fitting on AST rather than the one that was provided by mazdatrix... The reason I chose the old one was because it was 1.1bar vs. the new one is .9bar or something.

Thoughts?

spurvo

the 1.1 bar has higher pressure. The system will cool slightly more efficiently, but at the risk of failing hoses and/or O-rings due to higher pressure. For that matter, the 1.1 bar cap is probably pretty old and these things DO wear out after a while. Use the new one to see if it pulls coolant back in.

You are most likely losing coolant because one or more hoses has a small leak, which does not allow the system to pull coolant back into itself upon cooldown.

Or you have bad O-rings. Which would be a bad thing indeed. Ask me how I know...

supracosworth

Thanks Max, Spurvo. I have not the opportunity to examine the FC filler neck and was just concerned whether it has any special feature that cannot be replicated by just drilling a hole in the FD filler neck and brazing a runoff tube from it. Guess that's all clear now. I'll give it a try, take some pics and post it up here if it works.

XSTransAm

yes please let me know if it works... I will be doing mine right after you if it does