Wait, what? No thermostat in motor? I thought you said it was stock. You should run a thermostat.

I wonder if the water pump impeller still has all of its blades at full size.

I also wonder about an air pocket.

 

It had a thermostat (tried two) I pulled it out to see if water pump was moving water. It is, and air.

Still don't believe this so I did a compression test
1 170
2 170
3 175
4 180

 

1 - 4 left to right.

 

Plugs look good. Head gaskets are often misdiagnosed using the funnel. Let it warm up, you'll slowly see the fluid level rise as the coolant expands. Then the thermostat will open and the fluid level will fall quickly. That's when you need to stop the engine, pull the funnel, and cap the radiator. Any longer and you're just not allowing your coolant system to operate under pressure, which it needs to, and keep it from cooling properly. Once you do this, let it cool and then watch the pressure gauge. If it immeiately spikes to high pressure, you have a bad head gasket. It should slowly rise until your radiator cap pressure (usually 1.1 bar), then bleed down/up/down etc.

 

Did you pull your coolant out of a pond?

 

That's all I use.

 

So did you determine if it even is overheating yet? Unless I missed it you are getting ready to pull the head but no mention if you verified it.

 

Last drive I let it sit at the pined mark on gauge and I could hear it boiling when I got hood open. The plugs for an few hours of use have signs of heat on the electrode.
Far as I can tell its all it could be. Or cracked block or head.

 

I'd say HG, or a restriction that was missed, or WP. Just because you see flow, doesn't mean the pump is up-to-par. And yea that's some shitty coolant.

 

HG now changed, I'll put rest back together tomorrow. No real determining factor on the cause of the issue other than exhaust valves look a bit hot. Water pump looked ok, timing was right on, and HG looked ok. I'll put it new water pump in and cross fingers.

 

Oh if the head gasket was actually bad, and it was actually over heating, you'll need a new head and valve cover.

 

So I change the head gasket nothing remarkable didn't look bad change the water pump while I'm in there change timing belt start car up idle for 15 minutes brought it to 2,000 RPM started overheating again boiling out of the radiator cap interesting enough one of the heater hoses never got hot I had flush the heater core before had no issues. I've just bypassing the heater core we going to try that would a blocked heater core cause a car to overheat?

 

Bypassed it seems to run fine???

Could a blocked heater core cause over heating?

 

Well answer is YES!
Put many miles on it tonight, no issues. I have owned many Miatas and worked on many and never seen this issue before. Guess what I ll be checking 1st next time.
The new owner picked it up today and is thrilled!
Thanks all!
Now back to the slowest MSM build ever.