I've searched and could not find any threads directly related to this matter. I'm deleting the AST on the 20b and I have this 2nd gen Filler Cap Neck with the overflow tube. I didn't realize this piece was plastic. I see now, after the fact, that mazdatrix carries this item in aluminum, but too late I already possess the plastic OEM.

How fragile is this mazda part? Obviously its not as durable as aluminum, but what are the chances of this cracking, similar to the failed motors with AST cracks? Would you guys run this plastic neck?




I don't want to risk blowing up a freshly rebuild 20b because of a stupid piece of plastic lol. If it turns out to be a POS, then I'll be forcing myself to spend the $40 bucks on an aluminum or just run low pressure evans.

 

It should last at least 10 years without any need to worry about it. After that the nipple that protrudes can become brittle and break off easily especially when replacing the hose that attaches to it.

The aluminum piece doesn't have the nipple for overflow and would have to be modified to be used as part of an AST delete.

 

I originally did what you're doing.

However, when i drilled and tapped the nipple that you need to cut off that goes to the AST, when i plugged it, the side of the filler neck is really weak right there.

What i ended up doing is just running a hose from that nipple to the nipple on the bottom of the radiator to avoid it happening again.

 

Using that hose as a bypass is thought to allow a small amount of coolant to go "uncooled" before returning to the engine. It's best to block off the t-stat housing and radiator fitting...but if that isn't an option then running the bypass hose is "acceptable" but not optimal.

 

granted, but I figured it was negligible since I didn't want to risk cracking another water filler neck by trying to plug that nipple again.

 

I've never had one break. Been doing this a long time.

 

Ive never had one break in my 10years but they do get briddle. I always get rid of the AST on all the cars that come through here if available.

 

I bought a used one not knowing it was plastic at the time , and mine did break a bit . but it was old and green

 

Thanks, I guess Ill just run this piece for a while.

I actually did not drill and tap that AST line hole. I stuck a bolt into the hole and welded it around the neck with a good bit of filler. Coolant does not leak out and I didn't have to risk cracking/weakening the metal with drilling/tapping.

I think I'm going to do the same for the water pump housing turbo coolant necks as my turbo only uses oil. However, it would be nice to find some quality 3/8" silicon caps that can withstand coolant temps and pressure.

 

Yep your right, I guess this plastic neck is the only option.

I tried to drill and tap my aluminum neck with a 3an fitting, utter failure!

 

+1. when they get old, they change color, from black to green, and sometimes they will start leaking from the bottom, but i've never seen one catastrophically fail