Check engine light and thermostat

[talljames]

My check engine light (same as service engine soon) came on a week or so ago. Pretty sure it is an open cooling thermostat from what I have read. Temp needle at 12 o’clock and doesn’t drop down to 11 o’clock. Engine appears to still run fine. Need to hook up my foxwell.

Anyway, does anyone have any experience on how long you can drive with a fault open cooling thermostat?

I have a service in early February coming up. Maximum drives are around 45min. I haven’t lost any major coolant. Before the check engine light came on I was loosing little coolant over a long period and forgot to check for a while and suspect I caused the issue then.