Until recently, my thermostat rarely went past 20% with the possible exception of hot summer days with the A/C on. Recently it's been going to 40% regularly on mildly cold mornings & evening commutes. If my fuel gauge is right it seems to be burning more fuel than normal as well.

I've checked engine oil and coolant levels (last changed 3 years ago) and they seem fine. After driving 20 minutes to work this morning, the thermostat was at 40% and I let it idle in the parking lot for a minute to see if the fan would kick in. It did not... Any ideas what other tests to run to isolate the problem? Water pump last changed at 90k service. It has 160k on it now... I can smell the hot engine in the passenger compartment now and it sucks..

 

you have a problem with your cooling system if it only gets to 20%. normal is around 40%. so theres nothing wrong

 

Check heater core and hoses leading to it. Fans kick in at about half way point for a short time. If AC is off and your fans are on all the time you are short on coolant and are overheating the engine.