Chevy Impala SS Forum banner

1 - 8 of 8 Posts

·
Registered
Joined
·
11,032 Posts
The right fan should come on with the AC, and the left fan comes on with water temp.
 

·
Registered
Joined
·
3,008 Posts
With AC off, the secondary will also run when temps are hot enough.
 

·
Registered
Joined
·
1,587 Posts
Scott Mueller's answer has not really been improved upon since the late 90s.
Scott Mueller said:
B- & D-car coolant fans operate under PCM control at the following H2Opump temperatures and A/C system pressures:

Fan ……………… Mode ……… Temp ………… A/C Pressure
Primary (RH)…ON…… 107°C or 225°F……225 psi
Primary (RH)…OFF……104°C or 219°F……180 psi
2ndary (LH)……ON…… 111°C & 232°F……248 psi
2ndary (LH)……OFF……107°C & 225°F……203 psi

Additionally, the PCM will turn off the fans at higher vehicle speeds (above 48 MPH I believe), since running fans can actually impede airflow through the radiator at high speed.
Each fan also has a minimum running time. Once activated, the primary fan will run for a minimum of 50 seconds, and the secondary fan for a minimum of 26 seconds.
Finally, certain Diagnostic Trouble Codes (DTCs) may cause the PCM to turn on one or both fans.
Cars with RPO V08 have a [primary mechanical fan, and a] secondary electrical fan which behaves exactly as spec'd above; I.E.:
'ON' @ 232°F or 248psi (whichever happens 1st)
'OFF' @ 225° AND 203psi (must be under BOTH)
 

·
Registered
Joined
·
3,008 Posts
Does primimary mechanical fan have a clutch or does it run when ever engine is running?

It has a clutch - it freewheels when over a certain speed - IIRC 45 or so. Do yourself and your car a favor and do a mech fan delete.
 

·
Registered
Joined
·
171 Posts
Adjust fan turn on temps

I didn't like how hot the PCM allowed the engine to get before it turned on the fans, so I used Tuner Cat to edit the turn on temps in the PCM so that the primary turned on at 205*F and off at 200*F. I set the secondary to turn on at 210*F and off at 205*F.

FWIW and YMMV.

BTW, I have a NIB GM 3.42 ring and pinion I bought just before our 1995 Roadmaster got totaled. Doesn't take much to total an eleven year old car with 148,000 miles. PM me if anyone is interested. Also have the Owner's Manual and blue vinyl folder, five alloy wheels and center caps.
 
1 - 8 of 8 Posts
Top