Engine cooling fan ISX
10-31-2020, (Subject: Engine cooling fan ISX ) 
Post: #1
Engine cooling fan ISX
Hello been awhile and a great forum
I have same truck and it is 2009 T660 Isx 525/1850 motor
Having what I would consider a unique cooling dan problem I run local haul so routine is same every day as far as truck travels When I leave home in the morning after normal truck warm up and get about ten miles on the engine fan tries to come on but does not engage fully and belt is trying to slip as it’s doing this. The engine temps are not demanding the fan be on. When it tries to turn fan on the light is not coming on the dash either. I can also turn on the manual switch and then the fan will turn on fully as normal including the dash indicator showing it’s on. As soon as I shut off the switch the fan will stop momentarily and then try to do a partial engagement again. Here’s the baffling part. After this starts approximately ten miles into morning start it will do this partial fan engagement process for approximately 20 minutes and then it will completely go back to normal or proper running (as needed for normal operating). When I turn on the manual switch I do this to stop the belt from squeaking and to see if would help stop it from happening but it does not change problem
I have changed the solenoid that controls the fan located on firewall but to no avail. This problem occurs every morning of last several days and is almost right to the T as to the timing. Fan is acting like the air supply is is being lost partially (to start engagement process) I have checked air leaks on lines and at connections and see/hear no leaks and with that being said this problem on happens initially in morning and once it returns to normal it will not do again until the next morning
Looking for some ideas as what to check. Could the solenoid do a partial on/off due to a voltage that is not enough or ecm doing something? I guess the biggest mystery is the partial engagement of clutch and the fact that it only happens in morning
Thank you for any support of this weird problem!
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10-31-2020, (Subject: Engine cooling fan ISX ) 
Post: #2
RE: Engine cooling fan ISX
The A/C system if it gets low enough or if high=-pres. sensors is going bad on some trucks will try to switch on the engine fan.


User's Signature: ->: What I post is just my own thoughts and Opinions! --- I AM Full Of S__T!.
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 Thanks given by: Signature620
10-31-2020, (Subject: Engine cooling fan ISX ) 
Post: #3
RE: Engine cooling fan ISX
Why is the belt slipping?? It should not be even with fan on. Is your fan clutch good and tight when you shake the blades?

Have you tried key on engine off to see when fan clutch releases if the fan clutch was leaking air? Mine would leak air when the air was supplied to clutch to release fan.


Just a maybe that the seals in your fan clutch are leaking and when fan clutch warms up it swells the seals to enough to stop the air leak and release the fan.

Is yours a two speed fan clutch?

Just a few thoughts.

Now it being a paccar truck they love to engage the cooling fan when the AC compressor comes on. First time of the day turning on my AC it is just about guaranteed to turn on the cooling fan.


User's Signature: 2015 Kenworth T660
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10-31-2020, (Subject: Engine cooling fan ISX ) 
Post: #4
RE: Engine cooling fan ISX
Was wondering if AC had something to do with it. I have had truck shut off with key on and no signs of air. I have had fan switch on and off of course with engine off to actuate fan and then grabbed blades and no loose movements. Also took belt off with clutch engaged and spun it and tried rocking back and forth and again feels tight and solid
The belt was slipping when the fan clutch is having its fit because when this is happening it’s not fully engaging. So in essence it’s like you are restricting air to fan clutch but not all the way so fan is trying to come on partially and when it’s doing this the belt is gonna slip as the clutch is partially locking up or could be the friction surface of actual clutch disc making the noise. I have turned heater controls off as this happens and nothing changes either (no defrost heat air etc)
The idea that seals may seal after warming may be something. I would think that would do this as soon as truck started in morning but it takes a warm up and about ten minutes of driving before issue starts? I believe the fan clutch needs 100 psi of air to release and I don’t believe it is a two speed
Over the years it’s always either been on or off when working properly
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10-31-2020, (Subject: Engine cooling fan ISX ) 
Post: #5
RE: Engine cooling fan ISX
A lot of fans require air pressure to release, check if the air line is leaking while the clutch is released (generally engine off with key on and air pressure close to Max)
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