When temperatures are in the single digits, your engine is going to struggle to stay at 190 degrees F or above. I am running a 100% grill block right now with temps in the single-digit range. This is helping the engine run a little warmer and is a quick way to increase the intake air temperature by 20 degrees or so.
Originally Posted by codenamezero
A grill block can be done with $2 worth of pipe insulation from a hardware store. Just cut it to length with scissors (or razor blade) and jam it in your grill. Below is what I run when temps are about 30-50 F. Once temps get colder, I block the grill completely (including the mail slot in my 2015). I have a Scangauge and can monitor my car's coolant temperature.
If you don't have a way to monitor coolant temperatures, always be a little conservative and leave at least a small section of your grill open when the outside temps are above 20 F.
View my fuel log 2015 Mirage ES 1.2 manual: 51.4 mpg (US) ... 21.9 km/L ... 4.6 L/100 km ... 61.8 mpg (Imp)