Loud fan when starting?

Tiny
EMCCRADY
  • MEMBER
  • 2004 TOYOTA TUNDRA
  • 4.7L
  • V8
  • 4WD
  • AUTOMATIC
  • 260,000 MILES
Last night I got in my truck and started it up and noticed a loud unfamiliar sound coming from under the hood. It sounded like something might've been in the engine fan but from what I can see it's clear, after a few moments or a couple of revs it seems to fade and run normally. It's been in my family and well maintained for the past 15 years never had an issue with this before.
Thursday, December 19th, 2024 AT 7:58 AM

4 Replies

Tiny
KEN L
  • MASTER CERTIFIED MECHANIC
  • 51,603 POSTS
This can happen in cold weather because the fluid inside the clutch fan is more solid and forces the clutch fan to lock up and then loosen up to normal once the temperature is higher, but if you have never heard this noise before even in cold weather the clutch fan should be replaced. Here is the location of the fan and how to change it out. Check out the images (below). Please upload videos in your response of any problems so we can see what to help you with.
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Thursday, December 19th, 2024 AT 12:43 PM
Tiny
STEVE W.
  • MECHANIC
  • 14,515 POSTS
What was the temperature outside? If it was cold that could be the clutch on the cooling fan. They have a fluid inside them that reacts to temperature. When it is cold it gets stiff and needs to warm up a bit to free up. Usually that doesn't take very long because the shearing forces in the clutch generates heat fast. So, you might have heard the woosh of the fan for a few seconds and then it started freeing up. I might suggest having someone stand where they can see the fan with the hood open when you start it the next time in similar conditions. See if the fan spins up very fast, then stops making noise.
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Thursday, December 19th, 2024 AT 12:49 PM
Tiny
EMCCRADY
  • MEMBER
  • 5 POSTS
It was probably 20 degrees out so definitely below freezing. It's been this cold for a while though with no sound before today. I got gas today so I turned the truck off then on while it was warm and no sound.
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Thursday, December 19th, 2024 AT 4:36 PM
Tiny
STEVE W.
  • MECHANIC
  • 14,515 POSTS
Yeah that sounds like the fan clutch doing what they do. Once they warm up even a little bit the tend to become quiet again. Until the engine heats up then the fluid expands and the fan will start to engage until it gets hotter where it engages fully.
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Thursday, December 19th, 2024 AT 7:38 PM

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