Does anybody know if a bad thermostat would make the electric fans turn on? I have recently noticed my fans running on high without the temp gauge being above "normal" temp. As long as I have owned the car I have never heard the fans turn on before.... I tested the fan relay to confirm it is working properly as well as checked that the fans are both working as they should. The first thing I replaced was the temperature sensor because it seemed like the easiest (and cheapest) place to start. Now that I know the relay, fans and sensor are in proper condition, I am wondering if the thermostat could somehow be the culprit? I have no idea what else to check?? Coolant level is fine and still pink in color, and the overflow is at proper level... I hate not know why things are happening, lol.

Thanks in advance for any input!!

 

The fans switch on when the temp gauge reaches approximately mid way. Their job is to keep the engine at around that temperature.
The thermostats job is to block coolant flow until the engine reaches operating temperature and then open to allow coolant to circulate through the radiator.
If it stays closed then your temp gauge is going to rise fast.

If your temp gauge is showing mid way then normally the fans will cycle but if your environment is hot or the engine is generating a lot of heat, then the fan stays on until it succeeds in cooling the engine down again.

As I said to someone else recently, if you are really worried, get a laser thermometer and measure the temperature of the radiator core (NOT the AC Condenser!!) and of the engine block.
Sometimes it's easiest to measure the temperatures of the top and bottom radiator hoses. One is coolant coming from the engine to the rad (hotter), the other from the rad to the engine (cooler).
If any of those are above 220F then you have a problem, possibly with the Thermostat or the coolant/water pump. Otherwise just ignore it.

 

Thanks Boomer!!
The temp gauge has never gone above 1/2 way on the dash, but I am wondering if the thermostat is opening juuuust a little slower than it should so the fans kick on until it opens fully? I am going to replace the thermostat and refill the coolant this weekend as a precaution. I have no idea how long it has been since that service has been accomplished. I have owned the car for 2-years and not done it yet. It is fall in Wisconsin and the temps are gong to drop fast, so it'll be good to know its fresh coolant. I appreciate your reply and thoughts!!

 

In Wisconsin you are unlikely to have overheating problems.
Yes, fresh coolant is a good idea but I don't think the Thermostat change will make a difference.
However, once done you should have peace of mind.
Personally, I don't think you have a problem.

 

So, as a follow up I drained the radiator and replaced the thermostat this morning and it solved my issue. Now, I didn't think it was going to because when I looked at the coolant, it appeared to be brand new! Clear and pink, when I got the thermostat out I also was surprised to see that it also looked NEW!! After cleaning the mating surfaces and getting everything back together I was worried that it wasn't going to make any difference... I fired it up with the heater on high, and let it run for 20-25 minutes and then took it for a spin for another 20-25 minutes and I never heard the fans kick on, which was a great relief!! I did also notice that the fans were actually running, but at such a low speed that I couldn't hear them, so I assume that I had never heard them kick on medium/high speed before and they must have always been running as when they should have but I never noticed. I've included pictures of the old thermostat and coolant after I drained it. I'm amazed at how clean the inside of the radiator and thermostat housing are for a car that has 299,000 miles!!!

 

For others following along at home... is your A/C compressor running? (i.e. Your A/C is on)
Running the A/C will make the fans run so they pull more air through the condenser.

Also, the temperature gauge is a dummy gauge. There's a pretty wide range of temperatures the coolant will be at and the gauge will sit in the middle (something like 176F - 220F, don't quote me on those numbers). The fan usually triggers around 208F or so (again, rough number, I can't remember exactly).
The best way to know is to get a scan tool with live data output so you can read the OBD2 data for the ECT value (engine coolant temperature).

There's a chance the thermostat was fine and your system just needed some air bled out. Keep an eye (or an ear) on it, but not too hard--you'll go crazy.

 

It appears that every time I turn on the heater the A/C light comes on, so I assume the compressor is running. When I got home the other night I grabbed my IR temp gun and the upper hose was 187F and the hose just outside of the thermostat was 104F with an outside temp of about 40F. The fans had been running for the entire 10 minute drive home at a level that I could hear them inside the car. When they are on "low" or whatever I cannot hear them inside the car. I do have an ODB2 and a cheap tablet, but I always seem to have issues getting them to communicate.... I'll try to get them to play nice and try to get some data, which I should have done originally but I'm a stubborn old F#$% and thought it would have been easier to diagnose. I guess air could have been an issue, but it had been quite awhile since I had the radiator cap off, and where else would air get into the system? Thanks for the reply and suggestions!!

 

To me those temps sound entirely normal for a fully warmed up engine.
Coolant from the engine towards the radiator = 187F, coolant from the radiator to the engine = 104F, and the temp gauge in the middle.
I think it is more likely that you have something that is making your fan noisy like a leaf or piece of plastic in there, or maybe the fan control unit is busted.