2006 Ford Explorer Loud Noise underhood

It sounds like the fan clutch is engaging and you are hearing it. They are loud when the fully engage. Does it sound like a large fan turning on?

Yeah thats exactly what it sounds like. Why would that fan be engaging when my a/c is off? It seems I have plenty of coolant, so I dont think I'm overheating.

Could it be a bad sensor or thermostat?

The clutch fan functions based on a thermostatic spring that expands and contracts based on temp. If the under hood temp reaches a certain temp, it will full engage the fan and that is what it sounds like. If you open the hood, you will see the fan turns all the time when the engine is running. It just speeds up when the temp increases making that noise.

Let me know if you have other questions.

Joe

Ok, when you say the temp. "under the hood", are you refering to the actual engine temp. or rather that b/c it might be a hot day outside the temp. right underneath the hood is really high?

If its the radiator fan clutch turning on louder/faster I would have figured that its trying to increase cool air flow to the radiator b/c the engine is getting too hot.

The fact that the a/c is off, and that fan is spinning so fast I'm thinking 1 of 3 thiings... 1. the thermostat is giving an incorrect reading 2. the engine really is getting that hot (maybe b/c of low/leaking coolant), or 3. its just normal operation of the vehicle and shouldn't be all that worried about it

Sorry this is so wordy. I really appreciate all your help.
Thanks

It is under hood temp. Also, it sounds like it is working correctly. If I remember correctly, there is an electric fan that comes on with the AC which would help keep the temp down under the hood. Thus, the fan wouldn't need to fully engage.

Feel free to ask any questions you may have.

Joe