Green temp light stays on (after flush & thermostat replacement) Solved!

[Jake]

First off as a new user to this Forum I want to thank everyone who posts here. You have all walked me through many a fix for my 2014 Mirage Manual Transaxle beauty of a car. I have scoured through all the old posts but couldn't find anything relating to the issue I am seeing.
I recently changed out my clutch @ 160,450 miles and since I ended up pulling some cooling hoses for access I decided to drain and flush the radiator as well as get a new thermostat since I was down the rabbit hole. (I didn't want to top off the coolant with a different brand so wanted to start fresh) I purchased an OEM thermostat and installed and got everything buttoned up but now I have my green low coolant temp come on and stay on. Cabin heat feels warm and am comfortable driving, even in the Minnesota winter, but not as hot as when the light goes off. Should I try another thermostat or just put the old one back in since there was nothing wrong with it in the first place. used a coolant vacuum system so I don't think I have and air bubbles or leaks as it holds a vacuum.
Thanks in advance for your advice.

[Fummins]

Are you saying the green light stays on and doesn't go out or that the heater doesn't get hot when the green light is on? The light goes out when the coolant warms up to a certain temp(I dont' know the specs). So it's normal for it not to put out great heat until that light is off and it's driven for a little while.

[Jake]

It doesn't go out. It stays green the whole time.

[foama]

It should go out over about 60°C. Presumably it came with a rubber gasket around the perimeter? If not, thats the problem. Maybe you have a suitable thermometer to check if the new thermostat is shot?

[MetroMPG]

^ Yup, green light goes out around 137 F.

Do you have an OBD2 scan tool? It will show the coolant temperature that's being reported to the ECU/PCM.

EDIT: can confirm that running cabin heat at ~130F will feel warm, but not hot.

[Fummins]

I just pulled a thermostat out, it's impossible to install one backwards so there goes that theory. This one says 87C on it. Mine took quite a while to get warm this morning, warmed it up for 7 mins then drove for another 10 before I had a hint of heat. Even then the air blowing at the floor wasn't warm at all. But as I type this I remembered a bunch of the rubber plugs in my floor were removed and lost...
I don't know much it'd make a huge difference but did you have the jiggle at the top when you installed the new thermostat?

[Jake]

When I ordered a new thermostat it didn't come with a ring. And when I pulled the old one there wasn't a ring... so I just assumed maybe it was and internal gasket in the housing. After trying to install it wasn't fitting right so I double checked and saw that the gasket was left behind. I pulled it and inspected it... it looked fine so I used it on the new one. I also have an OEM thermostat from RockAuto sitting at my door delivered today that comes with an O-ring. Should I try the new one with the new O-ring or the original (which wasn't faulty, I just changed it for the sake of "well since I am down here" with the New O-ring? Also side note... how do you add a thank you to a post? I see them after certain comments and wanted to thank you all properly

[7milesout]

The thanks button is on the bottom left of each reply block.

Not much help but I'm on the side of the fence there was something wonky with the install. Trust the gauge / green light, it's just flowing through the thermostat area with no restriction.

[Fummins]

When I ordered a new thermostat it didn't come with a ring. And when I pulled the old one there wasn't a ring... so I just assumed maybe it was and internal gasket in the housing. After trying to install it wasn't fitting right so I double checked and saw that the gasket was left behind. I pulled it and inspected it... it looked fine so I used it on the new one. I also have an OEM thermostat from RockAuto sitting at my door delivered today that comes with an O-ring. Should I try the new one with the new O-ring or the original (which wasn't faulty, I just changed it for the sake of "well since I am down here" with the New O-ring? Also side note... how do you add a thank you to a post? I see them after certain comments and wanted to thank you all properly

The exact same thing happened to me with the gasket. How about that jiggle valve though.

[foama]

The original OEM gasket has a rubber ring = gasket around it. That gasket has a rectangular cross profile with a "slit" all the way around in which the perimeter (metal) of the actual thermostat is seated. The "Jiggler" (air escape hole) is on top. If the thermostat gasket doesn't seal, warm-up will take noticably longer in summer, and it might never achieve normal operating temp in winter.