I've only been wrenching for 50 yrs so this should be easy for me.  Did timing belt, water pump, etc.  Car was fine but for a water pump leak.  All back together and I cant get the bottom hose hot.  Thermostat isnt opening my guess.  I've put a known good one in and another.  Everything is fine with no thermostat, good circulation, etc.

I've burped it to the best of my ability.  Pulled a heater hose, pulled the throttle body hose.  There is no air in the system.  Thermostat is inserted into the block, tit out.

Not head gaskets, car was perfect before I apparently borked it.

What in the world am I missing??

5 hours ago, opus said:

I've only been wrenching for 50 yrs so this should be easy for me.  Did timing belt, water pump, etc.  Car was fine but for a water pump leak.  All back together and I cant get the bottom hose hot.  Thermostat isnt opening my guess.  I've put a known good one in and another.  Everything is fine with no thermostat, good circulation, etc.

I've burped it to the best of my ability.  Pulled a heater hose, pulled the throttle body hose.  There is no air in the system.  Thermostat is inserted into the block, tit out.

Not head gaskets, car was perfect before I apparently borked it.

What in the world am I missing??

Bad water pump? Maybe something dislodged and clogged a line?

It runs fine without a thermostat? How long was it driven without one?

How do you know it ran fine before all the work? Is this someone else’s car who told you that or you’ve been driving it for years?

You seem adamant it’s not, but this is the classic start of a case that ends up being headgasket. 

New water pump.  I flushed the block both ways and there are no blockages, nor clogged lines.

This is my car.  Its not the headgaskets.  I ran it 20 miles with no thermostat.  Its a new long block I built 9k miles ago.  I've been driving it daily with no issues.  You dont just drain coolant one day and have it all fall apart the next day.  There was nothing wrong with the car before I drained the coolant.

What I am thinking is that pure water is boiling fast, creating steam pockets and not letting the thermostat open.  Now that I have slept on it some.

You can always put the thermostats in a pot of water and bring it up to temp and watch them open.  

If you have a bottom radiator hose hot, you have flow through the radiator.  Proper coolant is a good thought and pretty cheap. 

I’d drive it and shut it off before it overheats so much it bubbles out, but after it gets warmer than normal.  Do that a few times and see if there’s coolant loss/air in the radiator and reservoir. What happens:

1. Levels all normal?

2. Radiator is low?

3. Radiator and coolant reservoir are low?

4. Or is it overheating so badly and quick that test isn’t possible?

Good, sounds like head gaskets but glad it’s not.

Those engines run fine on pure water, it will not overheat because it has pure water in it.

cool lower hose is indicative of air in the system which prevents coolant flow under certain conditions.

aftermarket thermostats and water pumps aren’t known to be be high quality. But those don’t explain your symptoms  

 

 

Using a Stant thermostat.  A thermostat is a thermostat.  Either it works or it doesnt.  I have put 2 of them in boiling water and the both open evenly.  2 days ago, the thermostat was fine.  I've done at least a handful of these with no issues.

When it was good and hot, I popped the thermostat out....the one that I have been using with no issues......it was still closed.  I honestly think its steam pockets thats causing it.

Lower hose is cool but trust me, there are no air pockets.  I pulled every line off the top of the engine and bled it that way.

Water pump has good circulation with the thermostat out.

You need a factory Subaru thermostat. The aftermarket one's never work correctly on Subarus. TAMA is the OEM manufacturer. 

Subaru uses a cold side control and it seems to be a problem for the aftermarket units. 

Also if you ran it without a thermostat and that is your basis for assuming the head gaskets are good - that's a false assumption. In fact we often gut the thermostat on cars that have internal HG failures to buy the customer a few months to figure out their situation since they won't overheat with the thermostat pulled. I've had customers gut the thermostat and drive 3 hours to my shop on vehicles that absolutely had fire ring HG failures and wouldn't drive more than 15 minutes with a thermostat in place. 

Edited May 13, 20232 yr by GeneralDisorder

The thermostat was just fine before I put the pump in, its not that.  There was never an issue until a pump the water pump in.  Head gaskets dont go. bad by putting a new water pump in. 

I do however think its the aftermarket pump I put in, cavitation.  I ran it without a thermostat for 20 minutes.

Disregard my advice and experience at your own risk. 🤷‍♂️

GD

23 hours ago, opus said:

I honestly think its steam pockets thats causing it.

Lower hose is cool but trust me, there are no air pockets. 

uh, seems to me if you are getting "steam pockets" then yes, there ARE air pockets... you need air to get steam,... Just sayin

and I will agree with GD about the aftermarket t-stat.. get a proper OE one and refill with the nose in the air... fill thru upper rad hose first, then radiator..

I've never had issues myself with aftermarket T-stats but I have found have crappy water pumps where the impeller falls apart or slips on the shaft.  If you are 100% certain about the integrity of all the other work you did and that the engine condition was fine before the repair, how can it be anything other than the replacement pump? With that in question, how are you actually determining that you have "good circulation"? 

same as Subaru  :::Stant 48457

Thats what it was.  Pump was either creating too much suction or thrashing too much air, etc.  Pulled thermostat, opened it up and stuck an aspirin in it to hold it open.  Put it back in, all is now right in the world.

Air lock ? I used to have this problem with an ol 96 outback I posted about here several years ago. Once I put the car on ramps and opened the bleeder valves on the radiator I was back in business.

 I hope you’ve already figured it out 

good luck

Edited June 3, 20232 yr by Toadspit