Usually my car is just up to temp by the time I get to work, after about 5/6 miles and 13 minutes.

Today it was up to temp half way to work and it was 4 degrees this morning, and I had the heater on at 24 degs

Other mornings it barely gets to half temp, evening on a warmer day.

How so??

Driving slightly more quickly will do it

Running engine to remove frost first?

Time spent in traffic?

Also when its colder, car uses more fuel to keep running, more fuel-hotter engine

You may have had a sticky thermostat before which has freed

Carryi.g weight in the boot.

Same routine every morning.

No idling on driveway, only me in the car, same route.

Same speed as it's twisting country road for most of the way.

I'll just keep an eye on it. I just think it's odd that it's warming up quicker in cold weather!

...... more fuel-hotter engine

actually, leaner fuel mixtures create hotter engine temps due to higher burning temps