Cooling system / radiator fans

I cant' say for sure what is going on with your car but if your coolant is really low the temperature sensor may not pick up the heat and turn on the fans. I would have your cooling system checked for leaks and perform a full system maintenance - hoses, flush, new coolant etc. Once the system is full of coolant, check to see if the cooling fans come on when the engine gets hot.

When I purchased the car the previous owner told me that they had to constantly put coolant in so I'm pretty sure there is a small leak somewhere. I was too scared to damage anything internally in the engine so I didn't try to drive it really hard after I refill the reservoir. If I were to turn on my AC at idle , and my fans kicked on would that rule that out ?

The first order of business is to fix the leak!!!

If the leak is from a bad head gasket (high probability) you will need to replace them. Use Subaru brand anti-leak in the radiator, it might help if the leak is very small.

How do you tell if the leak is coming from the head ?

How long have you had this car? I suspect that if you had this car for a while and it hasn't happened before then the radiator cap was the culprit. Radiator caps usually don't come off from overheat so if it was off then it probably was not replaced properly. When you refill the system be sure to put COOLANT back in and not just water

I've had the car for a week. I asked the previous owner of this is happened before and she said it has never happened. I refill the reservoir which nothing but coolant and have yet to drive it since

I know this advice is not well accepted with some members but the fact your driving a 12 year old car and head gaskets ain't cheep ,, I would try the old "Hail Mary" fix and #1 buy a new radiator cap #2 get Barrs leak stopper ,, then put it in the radiator. Odds may be good that it works BTW a perty sure way to tell if the gasket is blown is after the engine is hot (like about 10 miles) see if you exhaust has a lot of vapor ... put your hand close to it and see how much condensation you get ... check your oil, does it smell funny or look foamy?

The car is never had overheating problems just the small coolant leak that I know of. So I will more than likely replace the radiator cap and add that in and see if it works before I go on replacing anything else. And last time I looked at the oil ( a few days ago) it looked fine. No discoloration or foam

Bars Leak is nasty stuff. I would use the Subaru brand anti-leak or Alumaseal.

Why do you say that ?

Barrs leak has always worked for me but other products may be just as good

Have you ever seen Bars Leak? If so you would know what I mean plus people have told me it plugged up their radiator. I have had a 100% success rate for many, many years with the two products I mentioned.

If it were that bad it wouldn't be one of the top selling products /// in addition to that ,,, I told the gentleman to use whatever he feels is best Please use my email to discuss disagreements .. you confuse the people we are trying to help

Calm down, guys. The odds are indeed that the coolant leak is from #4 cylinder, requiring chronic supervision leading eventually to full HG replacement when the leak progresses, or is joined by an OIL leak from the opposite (right) head. There's onlyt a very small possibility that coolant loss is from a loose old clamp or seepage past a seal or wp bearing, in which case the Hail Mary of Bar's or similar (doesn't matter which...just don't use goopy oatmeal) could help. (Subie's red version isn't any better than Bar's...just pricier.) Tyler, if you get a light down under the left windshield to look DOWN at the rear corner of the left head you'll probably see active seepage or residue from seepage when cold overnight. That will confirm your diagnosis. Again, eventually the leak will progress so that it doesn't just seep out via gravity over night, but when parked and eventually actively driving. It is EXTREMELY important to NEVER run the radiator coolant level low, so if the overflow reservoir is empty be sure to fill the radiator EVERY TIME rather than just adding to the external tank; too many times folks run around with a full expansion tank and an empty radiator, blowing the head gaskets wide open indeed! Note also that if the former's happened you may also have now an INTERNAL (high pressure) hg broach which will percolate the coolant from the radiator out through the expansion tank and onto the ground. This will confuse you, as it's a different type of HG failure...but can NEVER be nursed along by adding coolant or any additive. But the first "slow" coolant loss can limp along for a few months-to-years if you're a good "wet nurse". Good luck.

PS The rad caps are very rarely bad, but high pressure percolation can ruin the rubber gasket and blow it off. That's another hint that the HGs are compromised internally indeed.