I have problem that my cooling fans turn on to early (before 200-210 F). How can I adjust then the fans starts and stops. I guess I need a OBD tool to set this in the PCM? And what brand, do I have to buy Tech 2? Or is it any other way to adjust fans start/stop?

 

To adjust the fans you should find someone with HP tuners. Normal OBD2 scanners will not allow you to edit programming.

I really don't think you need to reprogram anything unless someone was already in there messing around. You do need to what is wrong with the system. If you are going by the factory temp gage then there is a a lot more chance that gage is wrong compared to the computer sensor.

 

I read a text on Internet that GM had a lot of concerned new owners called their dealers regarding to their temp gage went up and down between 180 F - 210 F all the time. GM did something so the temp gage so the was steady at 200 F. Interesting if it could be confirmed in this forum.

 

I believe they turned it more into a 'dummy' gauge later on, 2000 maybe just like the oil pressure gauge change.

I genuinely don't think there's anything wrong. My fans cycle consistently, and often. Guage is always around 180-200 at the worst of times, and below 180 at the best, always fluctuations. Nothing to worry about man, the guage are never a fully accurate representation either, unless they're manual guage you've installed yourself.

 

what thermostate are you using? sounds like you may have a 180 thermo with a tune for a 160. or visa versa. or you got air in the system.

 

I have a new 180 F (the old one I installed for 4 years ago was also a 180 F). I don't think there is any air left. I have bleed and vacuum cooling system several times, and also drove the car. The temp never pass 210 F, but then the fans turns in, around 200 F, temp turn down to 180 F. I'm think the PCM start temp for fans is set to different than stock in PCM, as you said.

Settings for fan start to run should be:

FanMode Temperature A/C Pressure
================================================== ========================
Primary (LH) or Dual Low-speed Fan(s) ON: 108 C 226 F 248 psi*
Primary (LH) or Dual Low-speed Fan(s) OFF: 105 C 221 F 208 psi*
--------------------------------------------------------------------------
Secondary (RH) or Dual High-speed Fan(s) ON: 113 C 235 F 248 psi
Secondary (RH) or Dual High-speed Fan(s) OFF: 110 C 230 F 208 psi

*Note - this information is probably incorrect, although it is quoted from
the service manual.

 

How are you actually measuring the temp of the engine? The factory gages are and have always been crap. Have you looked at what the temp sensor for the computer is showing the computer?

 

test both coolant temp sensors.

4th Gen LT1 F-body Tech Articles

 

I measuring with both gage, OBD and digital meter. Yesterday I changed temp sensor, but no change. Fans starts to early anyway.