Technical Question

[alp]

Can anybody explain to me why when I start my 1999 T4R the radiator fun always works a full speed for about 30+/- seconds and then slows down and works almost silently. How this stuff works?
Thanks.

 

[MillerPKA]

Its the warm up process...many makes and model do this same thing

 

[alp]

As I understand the fun has a viscous coupling that changes its viscosity proportionally to the surrounding temperature. What I don't understand is why the fun always runs a full speed for the first 30 seconds no matter if it's 100 deg summer or -20 deg winter.

 

[CJ3Flyr]

It has fluid in it. In order for it to be properly engaged or disengaged the fluid has to be in the correct position. The fluid is moved by two things, the valve position controlled by the thermostatic control and centrifugal force. When the vehicle sits (absence of centrifugal force) the fluid migrates to the 'engaged' position. It takes 30 seconds or so to get the fluid back to where it belongs.

It's opposite but similar to checking oil... You never check the engine oil by starting a cold engine, running it one minute then shutting it down to check the oil. Why? The oil is thick and is in all wrong places to give an accurate reading on the dipstick. That's why we check it before we start it or after the engine is warm. (Warm oil can migrate back to the pan quickly.) Either way it's about having the oil in the right place. The fan clutch is similar, during that first 30 seconds everything is ok but the fluid is in the 'wrong' place...

Does that make any sense?

 

[BTO]

Normal for fan clutches. My Tacoma is even louder.
They call it the "morning roar".

 

[manhunter]

My 2002 does the same thing, I always wondered why - now I know.

 

[alp]

It has fluid in it. In order for it to be properly engaged or disengaged the fluid has to be in the correct position. The fluid is moved by two things, the valve position controlled by the thermostatic control and centrifugal force. When the vehicle sits (absence of centrifugal force) the fluid migrates to the 'engaged' position. It takes 30 seconds or so to get the fluid back to where it belongs.

It's opposite but similar to checking oil... You never check the engine oil by starting a cold engine, running it one minute then shutting it down to check the oil. Why? The oil is thick and is in all wrong places to give an accurate reading on the dipstick. That's why we check it before we start it or after the engine is warm. (Warm oil can migrate back to the pan quickly.) Either way it's about having the oil in the right place. The fan clutch is similar, during that first 30 seconds everything is ok but the fluid is in the 'wrong' place...

Does that make any sense?

Thanks Chris!
Now I've got it.

 

[01sr54x4]

:iagree: That was about as technical an answer as anyone could have given. Well done! I always wondered the same thing.