It's late, and my brain is fried. Stock D15Z1 in my VX hatch.

I went to swap my OEM thermostat back in, but discovered the lower bolt on the thermostat housing is rounded. No worries, I just filled it up with water until I can pick up an extractor tomorrow.

As I was burping the system with pure water, there were a lot of fine bubbles. I figured this was normal due to all the air in the system. I let it get up to temp with the cap up, and it was bubbling violently. My heart sank, as I've had head gasket issues in the past.

But then it dawned on me... could it have just been boiling? The cap was off, so it wasn't under pressure = boil-happy water.

I have a feeling I'm dumb.

Once it cools down a bit, I'll put actual coolant in it to verify.

 

when cold is it bubbling violently? that would be exhaust gas bubbles.

 

Nope, cold it just had a stream of fine bubbles, and the occasional burp... once it got hot, it was spewing.

I'll put 50/50 in it in the morning and check again.

 

normal.