So the car sat for 4 years with water in it... the thermostat housing ( i think that's what its called, new to rotary) so it's rusty and I'm wondering if it'll be okay to run this car? so it has compressions from what we've tested. when we drained the water it was clear. once we took the radiator off that was a different story the water was the same color as the cap. Also, the heater core lines are rusted when I took off the hoses. any help would be a lot, thank you!

 

As a first step, you might want to try flushing out your coolant system (https://www.rx7.org/Robinette/flush.htm).

 

Wow that is rusty! It looks like the nipple for the AST hose broke/rusted off, you may need to either replace that housing or drill/tap that spot for a barbed fitting.

Yeah, do a full flush and get it as happy as you can. If there's damage done, it's done, nothing to worry about on that now.

May want to think about just getting all the coolant hoses new from Mazda (I think it's around $120 for all of them) and maybe get a new water pump too.

Fill with 50/50 Prestone green coolant and distilled water. I buy a gallon jug of full strength Prestone and a gallon of distilled water from the grocery store, much cheaper than buying Prestone's pre-mix coolant. But, that will be after you get done doing a full flush and get it as clean as you can.

Dale