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Close to radiator cap?
No, close to thermostat.

If you just changed thermostat and coolant level is close to thermostat (coolant lost just to thermostat level), just fill radiator all the way up, trapped air will bleed automatically when thermostat opens.

Now, if you drain the system, trapped air might prevent coolant from reaching the thermostat, then you "might" need to purge trapped air (I have never done it in this kind of cooling system, jus on my Deloreans)
 

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Trying to remember, doesn't the thermostat have a little automatic bleed valve built into it?
 

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Trying to remember, doesn't the thermostat have a little automatic bleed valve built into it?
Most have it, that's why I said "you might" need to bleed it.

Seems like some still cannot understand this.

62404


THERMOSTAT JIGGLE VALVE AND BLEEDER VALVE
The thermostat jiggle pin is a pin that is located in the small hole in the plate valve of the thermostat and which should always be in 12 o’clock position during installation. It helps bleed the cooling system of trapped air by allowing air to pass into the radiator, after which it can be released from the system.
 

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Looking at Rockauto, there is also a bypass path built into the housing. There is a plug with a Phillips/cross shaped head, but I think if you turn it, you are actually just breaking it. The plug is just needed to cap the open part from the outside, needed to make the closed path in the part. Does that actually turn and work like a bleeder?

UPDATE: SEE MY NEXT POST

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62406
 

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Looking at Rockauto, there is also a bypass path built into the housing. There is a plug with a Phillips/cross shaped head, but I think if you turn it, you are actually just breaking it. The plug is just needed to cap the open part from the outside, needed to make the closed path in the part. Does that actually turn and work like a bleeder?

View attachment 62405

View attachment 62406
I've never tried, I'll never will, not really needed.

According to Sienile, seems like he's done before.

Again, despite what Sienile says, no need to bleed it unless you've drained the whole system.
 

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Ok, so I remembered I still had the original thermostat and housing from our '14. That plug I mentioned, definitely a bleeder screw. It's got an o-ring, a slot up the threads for flow, and the passage is only open to the engine side of the thermo.

There is a jiggle ball, also, built into the housing. It likely bleeds air on its own up to about the 3/4 line on the thermostat so coolant covers the center pin. At that point, the thermo should open when it gets hot and flush the rest of the air.

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Shining a light in through the engine side of the hole shows that the passage comes to an end at the bottom of the screw hole.

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62412
 

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Ok, so I remembered I still had the original thermostat and housing from our '14. That plug I mentioned, definitely a bleeder screw. It's got an o-ring, a slot up the threads for flow, and the passage is only open to the engine side of the thermo.

There is a jiggle ball, also, built into the housing. It likely bleed air on its own up to about the 3/4 line on the thermostat so coolant covers the center pin. At that point, the thermo should open when it gets hot and flush the rest of the air.

View attachment 62408

View attachment 62409

Shining a light in through the engine side of the hole shows that the passage comes to an end at the bottom of the screw hole.

View attachment 62410

View attachment 62411

View attachment 62412
So, what the verdict would be?

Is it absolutely necessary to bleed the system when replacing thermostat?
 

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It looks to me like it's set up to bleed itself and the bleeder screw is optional to use.
 
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And I found radiator cap losing pressure.
This is interesting. What does this mean? Was coolant leaking in the area of the rad cap?
If the rad cap is not sealing to the radiator, you have a problem. I had a similar problem where the cap was not pulled down onto the radiator hard enough to seal. I simply used some pliers to bend/squeeze the tabs or hooks of the rad cap that hold the cap on. This pulled the cap down harder on the rad and the leak stopped.
 

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That self bleeder valve isn't very effective. Never had one self bleed successfully without one of those 2 gallon screw on funnels.
 

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Well, I know I didn't bleed using that screw when I changed the thermostat. Just filled the radiator and leveled up the reservoir after running it. Everything seems fine, and it's been some time, maybe a year or so.
 

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Well, I know I didn't bleed using that screw when I changed the thermostat. Just filled the radiator and leveled up the reservoir after running it. Everything seems fine, and it's been some time, maybe a year or so.
No body does it!

Who in his right mind will risk breaking that plastic part doing something is not really needed?
 

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I've never used a bleeder screw or any other method when changing the coolant or working on the coolant system in any of our cars. I top off the radiator, squeeze the upper and lower hoses to get out most of the air, top off again, screw on the radiator cap, make sure there's enough coolant in the overflow tank, and turn it on to warm up the engine enough till the thermostat opens. I'll do a cold check after a couple driving cycles, but typically I don't have to top off the radiator, maybe add some coolant to the overflow tank.
 

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Who in his right mind will risk breaking that plastic part doing something is not really needed?
The person that designed it? :)
 
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