# Engine Fan Runs Constantly **URL:** \ **Category:** Maintenance/Repairs\ **Created:** [January 16, 2008, 5:23pm UTC](https://community.cartalk.com/t/engine-fan-runs-constantly/9501 "2008-01-16T17:23:38Z")\ **Posts on this page:** 9\ **Page:** 1
**Author:** ![chanyata](https://avatars.discourse-cdn.com/v4/letter/c/a9adbd/32.png) [@chanyata](https://community.cartalk.com/u/chanyata)\ **Post date:** [January 16, 2008, 5:23pm UTC](https://community.cartalk.com/t/engine-fan-runs-constantly/9501/1 "2008-01-16T17:23:38Z")
I just had the timing belt and water pump replaced on my 2001 Subaru Forester. Now I notice that the engine fan runs most of the time, even though the temperature outside is below freezing. I never hear it shut off either. The temperature gauge shows normal operating temperature. Before I take it back to the mechanic, I’d like to have some ideas of what might be happening. Could there be air in the cooling system that’s causing the temperature sensor to think the fan needs to run?? Thanks! ---
**Author:** ![SteveF](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/stevef/32/2_2.png) [@SteveF](https://community.cartalk.com/u/SteveF)\ **Post date:** [January 16, 2008, 6:27pm UTC](https://community.cartalk.com/t/engine-fan-runs-constantly/9501/2 "2008-01-16T18:27:44Z")
Not sure about the Forester, but some cars have more than one temperature sensor – one for the instrument gauge and one for the computer-controlled fan. Also, many cars combine both functions in the same sensor that has two separate components. It’s possible one has become unplugged or simply is defective. But that’s the place to start investigating. ---
**Author:** ![mr\_josh](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/mr_josh/32/3008_2.png) [@mr\_josh](https://community.cartalk.com/u/mr_josh)\ **Post date:** [January 16, 2008, 6:40pm UTC](https://community.cartalk.com/t/engine-fan-runs-constantly/9501/3 "2008-01-16T18:40:52Z")
Could it just be that you’re now very sensitive to what the car is doing, maybe a little more-so than before? Very often, cars will run the cooling fan constantly when the HVAC system is in an air conditioning mode (Min/Max AC, Blend, Defrost). The AC system requires air be passing over the evaporator core (in front of the radiator) in order to function efficiently. When it’s very cold out, try turning your AC system completely off and see if the radiator fan goes off too. If it does, you don’t have a problem. If it stays on, then you might be looking at a sensor issue. ---
**Author:** ![chanyata](https://avatars.discourse-cdn.com/v4/letter/c/a9adbd/32.png) [@chanyata](https://community.cartalk.com/u/chanyata)\ **Post date:** [January 16, 2008, 10:15pm UTC](https://community.cartalk.com/t/engine-fan-runs-constantly/9501/4 "2008-01-16T22:15:15Z")
Thanks. No, the fan is running most of the time, and I’m not using AC, or defrost, or blend. Today I was on the expressway and the temperature outside was in the low 20’s and the fan was still running. It seems very strange that this wasn’t a problem before the new timing belt and water pump were installed. Could air in the system be a possible culprit. ---
**Author:** ![chanyata](https://avatars.discourse-cdn.com/v4/letter/c/a9adbd/32.png) [@chanyata](https://community.cartalk.com/u/chanyata)\ **Post date:** [January 16, 2008, 10:18pm UTC](https://community.cartalk.com/t/engine-fan-runs-constantly/9501/5 "2008-01-16T22:18:42Z")
It seems very strange that the fan only began acting up after the timing belt & water belt were newly installed. Could air in the cooling system be an issue? Today I was on the expressway and the temperature outside was in the low 20’s and the fan was still running. I’ll have the mechanic recheck the sensors. Something is definitely wrong. ---
**Author:** ![Tree\_Hugger](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/tree_hugger/32/53_2.png) [@Tree\_Hugger](https://community.cartalk.com/u/Tree_Hugger)\ **Post date:** [January 17, 2008, 1:47am UTC](https://community.cartalk.com/t/engine-fan-runs-constantly/9501/6 "2008-01-17T01:47:41Z")
No. ---
**Author:** ![NYBo](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/nybo/32/17281_2.png) [@NYBo](https://community.cartalk.com/u/NYBo)\ **Post date:** [January 17, 2008, 4:11am UTC](https://community.cartalk.com/t/engine-fan-runs-constantly/9501/7 "2008-01-17T04:11:39Z")
Damaged or disconnected coolant temperature sensor. ---
**Author:** ![Craig58](https://avatars.discourse-cdn.com/v4/letter/c/3da27b/32.png) [@Craig58](https://community.cartalk.com/u/Craig58)\ **Post date:** [January 17, 2008, 4:13am UTC](https://community.cartalk.com/t/engine-fan-runs-constantly/9501/8 "2008-01-17T04:13:36Z")
That would also be my guess. ---
**Author:** ![hooches1](https://avatars.discourse-cdn.com/v4/letter/h/94ad74/32.png) [@hooches1](https://community.cartalk.com/u/hooches1)\ **Post date:** [January 17, 2008, 4:28am UTC](https://community.cartalk.com/t/engine-fan-runs-constantly/9501/9 "2008-01-17T04:28:05Z")
I would check all the wires to make sure they are connected properly, also if you have a relay (some are interchangable) that you can change out maybe try that (for the fan). Might be a bad temp sensor telling the fan to turn on.