Bought a new thermostat from subaru for my 84 bra, put it in and engine started over heating. Thought maybe it was water pump, so chsnged out water pump, flushed the system and still overheats. Pulled the thermostat and ran it without one, stays cool as a cucumber.

 

 

I tested the thermostat in a pot of boiling water, and seems to open and close. Didnt open far, but im unfamiliar with how much they should open. Its a 88°c thermostat, is that too high of a temp for my engine? Is there something else im missing here?

did you make sure the little air release hold was facing forward?  and did you run it on an incline to burp out the air?  both will help, you probably got an air bubble stuck in the thermostat.

did you make sure the little air release hold was facing forward? and did you run it on an incline to burp out the air? both will help, you probably got an air bubble stuck in the thermostat.

air release hold?

 

I ran it at idle on flat ground, took it for a test drive going both up and down hills and it overheated....

You have to run at idle until the thermostat opens. If the temp goes over normal shut it off. Then add a bunch of coolant. Do not drive before getting that air out of the water pump.

Commonly embarrassing question to answer to a problem like yours ... did ya possibly put the thermostat in backwards?

Meant air release hole, not hold.  Theres a little pin hole in the thermostat that lets air bleed off of the spring.  it is supposed to face forward towards the radiator.  the thermostat will go in any orientation but the air could get trapped and cause the thermostat to not function properly if that hole is facing rearwards. 

 

A lot of time level ground isnt actually level.  some people will jack up the front of the car to get it to purge.  the trick is to get the air bubbles to touch the hole.  its generally not much of a problem, it just bleeds as intended but stubborn ones do exist.

 

if the stat is functional and your not leaking then its likely air.  i dont know exactly how you do it, but start it up cold with the radiator cap off and fill it slowly as the car keeps drinking it.  just mentioning it in case you do something different.  I dont know the whole story from here lol.  after a minute or so it should stop taking water, and then close up the radiator and fill the overflow.  cycle it a few times through the heat range and keep and eye on it.

The thermostat must be installed with the sensor bulb and spring downward.

Commonly embarrassing question to answer to a problem like yours ... did ya possibly put the thermostat in backwards?

 

Lol i questioned it myself too, but no i didnt

You have to run at idle until the thermostat opens. If the temp goes over normal shut it off. Then add a bunch of coolant. Do not drive before getting that air out of the water pump.

Yes of course, i did that