Loud “Fan?” After startup

[larryq]

Just wondering , when first started, and you take off there is a loud fan sound that goes away as soon as the engine builds up heat
It sounds like a garbage truck.

I know it’s a normal sound, but I’m curious as to what is producing that sound.

thanks
L

 

[Signal73]

It’s the engine fan.

 

[larryq]

Had a feeling that was it, but wasn’t sure .
Thanks!

 

[Tuesdak]

Called “Morning Sickness” and a normal part of engine fan clutch operation. The drain back ports for the silicone fluid lined up when it was shut off and stopped spinning allowing it to migrate into the working chamber locking the fan on. And/Or it was locked in and running when the engine shut down thus still locked in on the next startup.

Rare, but, normal for it to not be locked up on startup.

 

[Signal73]

Called “Morning Sickness” and a normal part of engine fan clutch operation. The drain back ports for the silicone fluid lined up when it was shut off and stopped spinning allowing it to migrate into the working chamber locking the fan on. And/Or it was locked in and running when the engine shut down thus still locked in on the next startup.

Rare, but, normal for it to not be locked up on startup.

Thanks for the explanation. I knew there was a reason it would be locked up in the am but just never read it anywhere.

 

[Paul Binner]

Great explanation!! Would it be best to let it warm up before driving? Meaning, does it cause any additional stress on the fan clutch with it spinning so fast?

 

[Tuesdak]

Great explanation!! Would it be best to let it warm up before driving? Meaning, does it cause any additional stress on the fan clutch with it spinning so fast?

No: The fan runs locked up like this when needed after warm up. Like anything cold one should drive it sane till it warms up. Note all the emissions programming that wants to warm things up as fast as possible: so put a load on it and drive it for the warm up rather than a long wait with the "little heat" Diesels produce when idling.

The fan will kick out faster with higher RPM as the fluid drains via centrifugal force out of the working chamber. It moves slower, thus fan kicks out slower, when it's cold of course.

Point of Fact: on a cold engine I have had the fan come on in 1-2 blocks due to A/C cooling demand. The rare time(s) it didn't have morning sickness.

 

[larryq]

Top marks!
Great explanation!
L