Pros and Cons for Elimanating AST
 

What are the pros and cons for elimanation the AST?
and if there are no real cons then why dont people just take it out alltogether instead of replacing it with a aluminum one?

I believe M2 sells the removal kit for like $80 which would make it cheaper to remove the AST then replacing it, plus it would free up more room in the engine bay.

actually the by pass kit is only 60

I am not an expert....but there must have been some reason for Mazda to put the AST in the car. I would guess that eliminating it "could" cause some problems.

I have heard of some issues with eliminating it. However, I have never seen, or heard any documented problems with the elimination of the AST. Personally, I just replaced the plastic one with the Pettit racing unit.

I never looked inside the stock one to see the fins...but I might have to check that out.

Later,
Patrick

I think there are quite a few people here that have eliminated the AST and have had no problems.

My take on it is almost the same as pweizman. Mazda put it there for a reason, so I would just replace it not eliminate it.

I've been told the function of the AST is to eliminate the air bubbles in the coolant which come from the cavitation of the water pump. From what I understand these bubbles can cause miniature hot spots in the engine.

People say they don't have any problems after eliminating the AST, but then we also see a large number of blown engines, so I'm with the 'keep the AST' school of thought.

thers no "fins" in it...theres nothing..if i can get the pics hosted i have some good ones..all that the ast is is just a empty box, but the bottom line has a pin hole in it..kinda like the size of the stock boost pills...so water dosent flow through it as opposed to the rad...its there to elimninate the bubbles, granted thats mazda's explination, but how come its not on any other rotary engine????..i know someons gonna say b/c you need extra coolant for more cooling capicty, then how come the put a POS rad it it? the things like less than 1 in thick, plastic tanks...and a 195 deg thermo...seems like they made a mistake...i eliminated mine with no ill affects i knwo of..but i dont drive mine every day, so the bubles have time to dissapate in the over flow tank...it helps get rid of the bubbles but if 1 bit of air is hiding in the system its gonna have bubles....i say elim..but if u eanna pay 1XX.XX$$ for a tin can, go ahead..:rolleyes:
len

I've done both ... currently on the elimiation kit. The 1st & 2nd gens don't have an AST. It was an experiment .... who really knows if it worked. Some say the AST helps with extra coolant during engine transients .... but does it make a difference?

You can order the 2nd gen filler neck and get a pressure cap from your auto parts store for a total of $40. This is all M2 does ....

i am with spyfish on this one.

puma

from rob robinette site:

The air-separation tank is in parallel with the radiator. Once the thermostat opens, the hot coolant bypasses the radiator to pass through the tank, and is returned, hot, to the water pump inlet to re-enter the engine housing ports.

It's purpose is first to collect air/vapor in an upper, stagnant chamber. Then by thermal expansion of the fluid and gas, it purges the collected air into the vented overflow bottle by way of a 3rd hose that ends in the bottle below the coolant level. Air bubbles rise to the top and vent to the atmosphere. Upon cooling-contraction, coolant from the bottle is pulled back into the system.

The coolant that flows to the separation tank comes from the top of the thermostat housing, where a mini chamber is cast into the housing. The entry into this chamber can be seen after removing the fill cap as a 10mm hole. The only chamber exit is the hose to the separation tank. The purpose of the mini-chamber is to encourage any air that is passing below, from the open thermostat to the radiator, to rise up and be sent ( with coolant ) through the small bypass line to the separation tank.

Problems With Tank Removal:

IMO, simple removal of the tank and splicing the lines is not recommended for two reasons: First, it provides a bypass to the radiator that is not cooled. But more importantly, it encourages any air that may collect at the top of the housing to be pushed through the engine passages when the thermostat is open. Remember that air collection and movement to the separation tank was the primary function of the mini-chamber at the top of the thermostat housing.

bubbles are bad for cooling, mm-kay?

Thanks. I knew I read some where there were some bad things about eliminating the AST....

Many people have done the elimination with no problems though....so do what you wish.

To each his own....

Patrick

BTW: The 2nd gen does have something similar. My '86 that I had did not come with it, but when I started having air bubbling out of the overflow tank, the dealership added an AST type device. I think there was a TSB on it. Anyhow, I think the latter years of the 2nd Gen have a similar device.

My thinking is that if Mazda went to all the trouble of engineering it, it must be there for a reason.

I'd either just replace the stock one or go with a Pettit type unit.

Just my 2cents...

The other reason for an AST in the 3rd gen is because the top of the radiator is much lower in relation to the engine than in the first & Second Gens (air always rises to the higest point in the coolant loop)

ok well riddle me this how come the ast is lower then the top of the thermo neck?...if you do the elimination it(the top of thermo neck) is the highest point in the coolant system:D

I got rid of my ast and so far I have had no ill effects. i don't really think you need any kind of kit. all you need is a radiator cap from an '86 and a couple of small clamps. I got the kit with my ic and I didn't even use a lot of the stuff.

Well you hear people say "I've had no problems" but how do you know? It's not like elimination is gonna make the car fire funny and sound different and in most daily driven situations the temperature increase is not noticable. But to allude to a point before, no one can possibly run a controled experiment to actually find out if the bubble pockets cause motors not to last as long because there are just too many other factors involved. So really it's impossible to conclude one way or another, but cooling theory suggests the AST is beneficial and elimination is harmful.

I've always said to keep it in. Mazda did 7 years R&D on this car, which carries a lot more weight with me than some backyard experiment and "the previous RX-7s didn't have it" logic.

just for shits sake...7 years of R&d and they came up with a plastic box with a seam you can pratically pull apart by hand??:rolleyes: they over enginered almost every other system but put that pos on one of the most vital systems....boggles my mind...ive never see a pettit or one of the others but is the bottom nipple only a pin hole? like the stock..if not its the same as eliminating it...the small hole on the bottom is there to restrict coolant flow through the can...basically it just lets the air bubles in but keeps the coolant flowing hrough tha rad wich is how the stock dose..this is the biggest problem with the elim..you just jump the hose from the top to the bottom..givin a easy bypass arround the rad..its not that much but if u wana do it tap and thread thrmo nipple..put pipe plug in, and get the bottom nipple on rad welded closed(only on aftermarket rad).....i think its all a matter of opponion. just liek who uses preston, texacobrand..peak...its all what u want...
but you are right mazda put it there for a reason:D
https://www.rx7club.com/vforums/atta...&postid=224912

Yeah Bacon, the splitting seams are kinda funny when you think about it. I guess that's what happens when they don't have 5-10 years to really field test everything and then prototypes get shifted towards mass-production. Plastic-tanked radiators split over the years on all kinds of cars, and the FD3S runs hotter than most cars and is driven harder. So I guess it's pretty easy to see why the split happens and how Mazda overlooked it ... but it is kinda silly. I guess if they had more field tests of production versions then they would've corrected it and this thread and debate wouldn't exist. :)

true true....
heheh..so dose the 98-99-00 have a meatal one? or one @ all?

if it still has the plastic one, mazda must just be idiots:rolleyes: :D

I eliminated mine and have seen no problems. I've heard of the Pettit AST having problems - either leaking or overflowing - can't remember which one. As far as Mazda doing R&D on the FD is funny. Look how many "stock" FDs needed engine rebuilds at 40K or new turbos at 50K. Their coolant seals that they spent so long researching usually fail. I was at KDR with my car with a coolant seal failure and needed a new engine. There were 18 other FDs up there that need the same thing. They put one of the most complicated twin-turbo systmes in a car that periodically works if at all. When it does work, it rules - when it works. Ever try troubleshooting 400 miles of vacuum lines? Why didn't Mazda put an aluminum AST in the car to begin with. The stock one is awful. I don't buy the Mazda R&D thing. It took aftermarket tuners to come up with ways to fix a lot with what they did wrong. They did make us a sweet car, but could have spent a little more time R&D about reliability.

Buy the R&D thing or not, there had to be a perfectly good reason for them to add something like an AST to a cooling system. That's my point ... and cooling theory/physics/chemistry supports it.

I've said it before and I'll say it again ... the car should've never been sold to the public. It can't be treated like the average consumer car and the price range it fell into made it affordable to idiots or people that don't know any better. It's higher maintenance and requires more knowledge to own than a Ferrari, yet it fell into a Corvette price range. Ferrari owners know and can afford to have their weekend driver pampered by a mechanic. Most Corvette owners just have erectile difficulty and owning the car is mindless. The FD fell into this same demographic and who was gonna tell them what they have to do to keep the motor from popping ... the salesperson?!

First I'm going to piss some of you dorks off! You know that the FD is a great car but was made with a few well known design problems. If you do not know what they are, then you do not have the experience with this car so do not have the right to make qualified judgements yet. With these known problems, some of you still have the stupidity to say "The AST must have a purpose, they made it that way". DOH!!!!!!!!!!!!!!!!! Ask some owners who have real heavy experinece working on FDs what they think of many of Mazdas FD designed parts.

Even with the AST removed, there is an area for air bubbles to collect and be expelled. That is right under the cap on the thermostat housing. These so called bubles can still be expelled into the overflow tank.


Now lets talk about air bubbles. The only air bubbles (we are not talking about steam) that can form are from the disolved air in the water used in the cooling system. This is a very very small amount and once it is expelled, it is gone. The only real air bubbles to contend with are the ones present when the cooling system is first filled. These are trapped air, not dissolved air. These will free up and move around during the first few days of running the engine. It is very easy to check you cooling system after cool down for a few days after refill if this worries you.

If this still bothers you, find your mother to hold your hand!

i must say i agree with cewrx7r1, there are so many parts that are too much complicated and other parts that have been put there for nothing. There is security over security over security. People who knows their car and knows how to do the maintenance on them don't need those securities.

Example, the double throttle actuator. People are removing it without havng trouble, you just have to be carefull when the car is cold. This was one security that someone who knows how to drive won't need it. Or the PCV valve.

Everything is way to much complicated on this car, just look at the brake fluid reservoir... or worst, the sequential turbo system...

My main goal for the next year is to get rid of every protection or double protection so that the car wil get easier to work with.

i will do every single mod like that on rob robinette site's

puma

My only two cents is that with the aluminum AST I don't have to worry about it exploding and I can hold a little more coolant than without it.

Agree....if it didn't need the AST you think Mazda would put it in the thousands of rx7 they made? They would save themself some money to just not install it at all.

Like DK said, HOW would you know if there's any immediate ill-effect when it's eliminated? You don't, and when your engine is blown, you think it's oh I ran lean...high boost...bad tuning...cold weather...that's bullshit!!!

Why do we have so many blown Rx7? Because people think they can start removing things from the Rex because they think that they're better engineers than the engineers that built the car. I have to admit, a lot of upgrades we do is much better than the stock ones but that's UPGRADE...putting better parts in PLACE of the inefficient stock parts.

So for your own shake, please pay a little more and get an AST from Pettit or something.


IMO.

Mark

The ol' "Mazda knows what they're doin so leave it there" argument makes sense but doesn't persuade me that much. Its not like mazda put in everything the car needed...AHEM boost gauge! even t2s had it.

cewrx7r1 noted that with the elimination kit the job of the ast is still performed which is true. so i'd lean towards tossing it. i've done it 2 3rd gens in a row now. and as for people's engine's blowing up possible due to this...you can tell why an engine goes upon breakdown. i haven't heard the 'my seals went when the car overheated because i bypassed the ast'. granted there may be some other mysterious drawback, but has anyone seen it?