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Coolant temp drops at idle, rises once moving

5K views 8 replies 5 participants last post by  Chase_fg1 
#1 ·
Hey y'all. I have an 06 FG1 and when it's extremely cold outside (like -10 or colder, I've found that if it's more than -10 it doesn't happen at all), she won't warm up at idle, but once I get going she warms up again.. until I hit a stop light, then the coolant temp starts dropping as if I've turned the car off. And once I start moving again, sure enough the temp rises back to normal. I've had 4 other cars and this has never happened so I know its not just the extreme cold. Thermostat stuck? Maybe it's just the guage acting funny? Anyone have experience with this? Let me know, thanks in advanced!
 
#7 ·
Replace the thermostat and bleed the system. Should most likely fix it.

My drive to work yesterday was -18F and once it warmed up the temp never fell.
You can also boil your old thermostat and see if it opens. Make sure to boil it in distilled water otherwise it will get all covered in oxidation from the minerals in tap water. I bought a cheap thermostat from the autoparts store once, and it looked like a piece of garbage so I decided to boil test my old one, and it still worked fine so I put it back in and bled the system and my issue went away.
 
#8 ·
On my 2008 EX, the gauge started acting this way when the weather got as cool as even 50 degrees.
I replaced the thermostat and problem went away.

Maybe it's just the guage acting funny?
The first thing to try is once the car is warmed up, give the gauge a stern talking to and let it know this is serious business and quit acting funny!
On a serious note, it is not likely the gauge.

She's only got 89000 miles, I got the car with 80000 miles. ... Also, ive only lost a very small amount of coolant since I got her (I'd say barely a quarter of a quart)
So about one cup. In 9,000 miles if that is all it has lost, I would chalk it up to some evaporating and there may have been a little air caught in the system.
If you had a serious problem, it would likely lose a lot more than that. Although to be fair, it is never comforting to have to top off fluids. ONE thing though - if you are checking fluids on a cold engine, the drop in temperature will make them all look a little low because of contraction. I always check all mine when the car is warm from driving.

You can also boil your old thermostat and see if it opens. Make sure to boil it in distilled water otherwise it will get all covered in oxidation from the minerals in tap water. I bought a cheap thermostat from the autoparts store once, and it looked like a piece of garbage so I decided to boil test my old one, and it still worked fine so I put it back in and bled the system and my issue went away.
I would think if someone were going to go through all that hassle, might as well just replace the old one.
 
#9 ·
On my 2008 EX, the gauge started acting this way when the weather got as cool as even 50 degrees.
I replaced the thermostat and problem went away.


The first thing to try is once the car is warmed up, give the gauge a stern talking to and let it know this is serious business and quit acting funny!
On a serious note, it is not likely the gauge.


So about one cup. In 9,000 miles if that is all it has lost, I would chalk it up to some evaporating and there may have been a little air caught in the system.
If you had a serious problem, it would likely lose a lot more than that. Although to be fair, it is never comforting to have to top off fluids. ONE thing though - if you are checking fluids on a cold engine, the drop in temperature will make them all look a little low because of contraction. I always check all mine when the car is warm from driving.



I would think if someone were going to go through all that hassle, might as well just replace the old one.
Awesome, I've already got the OEM thermostat and likely gonna do it soon. Hopefully it's as simple as that.
 
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