Drove the old girl out for the first time in a while, everything was going great until I noticed the gauge rise during some spirited driving in the rain on a cool day. I let off and it held for a few minutes until it naturally pegged itself just below the red H line
I immediately pull over to stop, the idiot alarm rings, expect to open the hood to an oven.
ICE COLD.
I rip out the air box and yep the hoses and rad are ambient.
Just my luck and it's raining.
The heater blows hot though so that was a blessing. Some kinda cooling can happen.
I walk down the road to a convenience store for water, just happen to have my lisle funnel refill the coolant it puked out and I still can't get the water to flow through the radiator.

At this point I limp it home going 20mph with max heat on and it actually seems to work it's not quite H but just below. Luckily home was less than a mile away. Oil coolers doing their part it seems.

So is this a broken thermostat? It seems like it to me.

If it is should I get OEM or aftermarket? I've seen a few things saying the OEM Mazda keeps falling apart and well aftermarket seems to be the same... Anyone with long term luck with a thermostat?

Should I replace my water pump too? I can't imagine it appreciates boiling temperature and high pressure.

Engine starts hot/cold fine. Luckily so I imagine it's not blown.

 

Sounds like a thermostat yes. The oem mazda ones come with a the gasket now just so you know. You don't have to buy it separately. It wouldn't hurt to replace the pump as well since you're going to drain the system anyway.

Before you install the thermostat, actuate it a few times with your hands. We had a brand new one stick on us. Tore it all down to check it and sure enough it was just really sticky. Broke it free and it was fine after that.

 

I experienced the same thing last October. I had driven the car the previous night without issue. The next morning, I started up to idle up to reasonable temperature, and noticed my coolant temperature was rising very quickly. This was a rather cool October morning. Shut it back off, and the radiator was ice cold. Started again, and had the same issue. This was a new OE 180F thermostat. After getting another OE replacement, I boiled them both and noticed the defective one was cocked as it was trying to expand. It fully expanded, but not until 190-200F. Maybe a bad batch of OE thermostats? Anyway, the new one looked like it was working fine so I installed it. Not many miles since, but it has been working fine.

 

PSA: if you buy a thermostat from Mazda USA you get 8AF6-15-171 -9U which is NOT the OE thermostat!
the OEM is an NTC Mazda Japan (and Canada) sell N3A1-15-171 which is the genuine part. this one needs the gasket N3C1-15-173

i also like to boil my thermostats. the opening spec in the FSM is the MINIMUM, a new thermostat opens more than twice that

 

got mine from atkins which didn't have the gasket.
prob the oem ntc one
car runs cooler now with new thermostat and mazmart waterpump

 

the Atkins one was a surprise, its Motorad i think, and when tested it worked as well as an NTC.

 

Atkins has a habit of passing off aftermarket parts as OEM...

 

I got the parts!
N3A1-15-171 THERMOS
N3C1-15-173 GASKET
They sold it to me as a set.It looks nice, I'll be sure to boil test it hopefully it'll be straight...
this one looks fairly nice, even has a jiggle pin so I don't really need to drill a hole in it.
I'll post the photos later on gonna compress them a little bit for the site.