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2003 chevy trailblazer_ls_ext
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24 Posts
I just received my Trailblazer service manual on CD ROM from GM Parts and Operations. Here is a direct quote concerning the operation of the fan clutch:

The PCM commands the cooling fan to 100% under the following conditions:

*Engine coolant temperature exceeds approximately 129°C (264°F).
*The transmission oil temperature exceeds approximately 151°C (304°F).
*A/C refrigerant pressure exceeds 1655 kPa (240 psi).
*When certain DTC's set. These include P0116, P0117, P0118, P0125, P1481, P1482, and P1484.

After reading many of the posts here concering engine a trans temps during towing I thought it would be a good idea to post this here. What alarms me is the extreme temps that these are allowed to reach before 100% cooling is commanded.

A few questions:

1) My temp gauge only goes up to 260 so why is the coolant allowed to reach 264* before 100%? Doesn't a 50/50 mix of ethylene glycol/water start to boil at this temp under 15 psi?
2) Dosen't the transmission fluid begin to cook at temps below 304*. My '03 TB came with Dexron 3 or 4 not Dexron 6.
3) I know that the fan does cool at a reduced coupling (< 100%) below these temps but why would we ever want them to get this high for the sake of saving a little fuel?
4) Can the PCM be re-programmed to command 100% at reduced temps? Would a tune do this?

Please,.. any and all comments welcome!
 

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2002 olds bravada
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2,369 Posts
hm..its funny how the PCM commands the fan clutch to run at full potential AFTER everything starts to boil up and fry..:rolleyes:
 

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2002 olds bravada
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2,369 Posts
I'm pretty sure anyone with a TechII can command the PCM when to turn the fan clutch onto full power..
 
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