While driving last night the check engine light came on and it read a code P0128 which means that the coolant temperature is below the thermostat regulating temperature. Last night was the first cold night we've had so I feel like it has to do with that and that the thermostat is stuck open and not broken. If anyone has experienced this before what did you do to fix it. I don't want to replace the thermostat if it can't be unstuck by flushing the coolant.

 

I'm sure now that the thermostat is stuck open, does anyone know if flushing the coolant can fix that, or anything else that can

 

There's only one way to fix a broken thermostat, replace it! You could change fluids for ever and it won't fix what's broken/failed. Consider yourself lucky, if it would have failed closed you would have had overheating issues....Gary

 

Buy an aftermarket one too. Since you have to replace it, just upgrade.

 

After market thermostats are not an upgrade, that's like drive belts the dealerships carry the best quality. His thermostat failed in the best possible way, keep it in the family....Gary

 

^^ +1

If you want an upgraded thermostat go Nismo.

 

My nismo thermostat gave me +10 bhp. It also came with a sticker good for another 5.

 

I probably should have upgraded but I just got the regular one, it was 160 for the thermostat, coolant, and labor

 

Reviving a really old thread. My check engine light came on yesterday and just pulled the same code. I guess mine failed opened cuz the check engine light came on while I was driving, just like the OP. I had just replace the OEM one with a Mishimoto about 6 weeks ago also. Nothing wrong with the OEM one as it was still working like a champ. My friend told me to change it also because I was flushing my coolant to get ready for winter. Lucky I still have the OEM one. Just need a warm place / garage to re-install it. Damn Chicago weather is too damn cold nowadays.

 

Is the Mishimoto one that you put in rated for the same opening temperature as your OEM one or did you go with a lower temp rating?

 

I went with a lower temp rating one. Bought it off fleabay for $60 and the seller did have a 99% rating. Just like this one...............

https://conceptzperformance.com/Cart...on.php?II=5323

Is there a difference? good? bad?

 

That lower-than-spec thermostat is definitely why it's doing it then. The motor isn't reaching the specified coolant temperature in the required time, so it's tripping the P0128 CEL code. Our cars actually run pretty cool for the most part so there's not much of a need to use a lower temp thermostat really. When I drive in temps below 50 degrees, my car tends to hover at around 170 to 173 coolant temp as long as I am moving. That's extremely low for a 3.5 V6. My 2.7 4-cyl Tacoma runs cool as well, and that thing is usually in the 177 to 185 range regardless of conditions. I don't think I've ever owned a car that maintains such a low coolant temperature before aside from my G.