So, my thermo neck was cracking and slightly leaking allowing air into my cooling system. Finally got the parts this morning and it took roughly 30 minutes to do.

Got the parts from mazdatrix. Aluminum neck, stant thermostat, and associated o-ring.

My original thermostat was well worn and so was the o-ring. The o-ring was all flat and deformed so it definately needed replacement.

So here is what I found when I removed the thermostat. A piece of what i think is outer coolant seal. It is black and rectangular shaped, not round. It has faint lines on 2 sides and smooth on the other 2. The piece is about half an inch long.

I don't have time to take pics, but I will tonight of the old thermostat and the piece of seal that was lodged in it.

 

That sounds like a piece of coolant seal to me.

 

And that is the strange thing...I have no signs of coolant seal failure at all.

I am not loosing coolant, I don't have exhaust coming out of the radiator, it is strange.

I am going to take a picture of it later today and post it. Been busy and havent had a chance to do it.

 

The black coolant seal is on the outside, so if it were leaking, it probably wouldn't be in the combustion chamber.

 

^ That's true.

OP: Do a pressure test on the coolant system. And is this a rebuilt engine?

 

Nope, original engine from factory.

I don't have a pressure tester on hand so I'll have to get my hands on one.

Also, I do routine and rather thorough checks in the engine compartment every week and there is no coolant leaking anywhere. This seal is relatively straight so I would imagine it would have come from the straight side of the rotor housing it this is what it is. Definately no leaks there.

I am taking a picture right now...I'll post it up.

 

Here are pics....

First two for detail, last for size comparison.

 

Still looks like a coolant seal to me.

If you can't pressure test it, try the bubble test.

 

Now I have done that, and no compression loss that I can tell.

Freaky.

 

Wait... maybe others will confirm but I say no to coolant seal upon seeing that. That looks like the t'stat neck to water pump housing gasket. It pinches off when you tighten it, hanging off the sides (or in yoru case internally). It kind of looks like plain rubber. The coolant seal doesn't look like that IIRC. Plus you say no leaks, inside or out. Finally, the initial leak was in that area.

 

Nope, the thermostat neck oring looks totally different, and it was all intact still attached to the thermostat when I removed it. The original leak was a large crack in the plastic neck.

 

Son of a bitch.

I did an engine bay inspection today and found that the aluminum thermostat neck I bought from mazdatrix has 2 casting flaws in it. There are two small cracks. One at the base of the neck, at the flange, and the other just all alone on the neck itself.

What a pain in the ***. My last part I bought (not from mazdatrix), the water pump, didn't have the pulley boss pressed on correctly. Now this? I HATE having to redo repairs due to faulty parts.

Will I have to get another freaking o-ring for the thermostat too?

 

That is NOT a coolant seal IMHO. Looks more like the thermostat O-ring.( I assume your S5 then)

Are you sure the cracks on the thermostat neck aren't just casting marks? Ive seen front covers and a few various other parts with "cracks" that really are just casting marks. Take some pics for more opinions.

 

Nope, not casting flaws, I thought that is what they where during my initial inspection of the part before putting it on. They are leaking slightly and leaving that "trail of tears" dried coolant crud.

I'll get some pics tommorow.

 

Bummer to hear....

 

Why don't you see if they'll replace it?

 

Have had other things going on, so I just now called mazdatrix this morning....

GREAT GREAT company. Took all of 5 minutes. They are sending me a new neck and oring for the thermostat, and a prepaid box so I can send the defective neck and the now unreusable oring back to them. Badass customer service. They didn't even question me about it.

 

there's no possible way that the outer coolant seal failed and went into the cooling system. don't ask me if it is or how it got there, just throw it away and forget about it.

/thread end