I've got a 2008 Mazda 3i Touring, 5 speed manual, with about 145k miles on it. A few weeks ago, after my wife got home from work, we noticed the coolant temp gauge on the dash was fully at high and there was a slight burning smell. I don't know how long the gauge had been at high, but her commute is about 10 miles in a mix of stop-and-go and highway traffic.
I checked the coolant reservoir (the front passenger side of the engine compartment, right behind the washer fluid reservoir) and it was low. I put in about 1/2 gallon of coolant (premixed), and haven't seen any leaking out since.
At the same time, the check engine light has been on (first on since April). Back in April I had an auto store read the code, and it showed P0446. I didn't do anything to address that at the time, and the auto store didn't clear the code or anything.
Even with the additional coolant, the temp gauge will creep up towards high while driving, but it tends to go back down (to 1/2 or 3/4 of the way to high) as rpm and speed fluctuate. I don't drive it far now, usually only a few miles each way and only a couple times a week.
I had the auto store read the engine codes again today, and this time there were 4. P0446 showed up twice, along with P0117 and P0126. I also noticed a bit of a burning smell from the engine area after I got home.
The last two codes seem to be coolant related, based on my quick Google search, but are they a cause or a symptom? What could be causing my coolant to continue running hot?