Radiator fan(s) / Thermostat Questions - GM Forum - Buick, Cadillac, Chev, Olds, GMC & Pontiac chat


1992-1999 Series I L27 (1992-1994 SE,SLE, SSE) & Series II L36 (1995-1999 SE, SSE, SLE) and common problems for the Series I and II L67 (all supercharged models 92-99) Including Olds 88's, Olds LSS's and Buick Lesabres Please use General Chat for non-mechanical issues, and Performance and Brainstorming for improvements.

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Old 08-05-2005, 02:45 PM   #1
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Default Radiator fan(*) / Thermostat Questions

Hello All,
Just bought a used 97 3.8 SE FBI Bonny with 103,870 miles on it.
All fluid levels were fine, Engine runs great, shifts great, A/C works great. Looked in the oil intake and springs and all were nice and shiny. Alarm is a pain though, I think I am getting out the snips.
I'm gonna change the oil, change tranny filter, and flush coolant and wanted to put in a 180 thermostat.
Coolant looked a little mucky on underside edges of cap and on edges of reservoir.
I do not have the owners manual or a Chiltons manual yet.
Two questions:
1. There are two radiator fans.
The drivers side seems to work normal.
The other is on the Passenger'* side of the radiator and does not seem to come
on, I would think it should come on with the air conditioning (right or wrong). If it
should, what could be the problem?
2. Is there anything that may be "tuned" to work off the stock thermostat that will
be adversely affected by putting in a 180 thermostat?
Thanks, Bob
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Old 08-05-2005, 05:06 PM   #2
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1. Yep there is a high and low setting for the fans. both should come on with the a/c.
2. Nope. Nothing has to be tuned. The 180 will work no problem.
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Old 08-05-2005, 05:11 PM   #3
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On the fans, both fans should come on at both speeds. The only thing that changes is the speed they operate at. Once the A/C is requested both fans should come on at high speed.

Each fan has a seperate connector and I believe a seperate resistor as well. (two resistors on the driver side fan) If my hunch is right it'* one resistor per fan.

Another thing to keep in mind is low speed fans turn on at 215 degrees, and high speed fans turn on at 225 degrees or when A/C is requested.
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Old 08-05-2005, 05:14 PM   #4
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1. Both fans should run with the a/c on. They are connected in series for slow speed and parallel for fast speed.

2. The stock pcm will not turn on the fans untill the temps reach 195*f, if you put in a 180 tstat there is a chance the car will be cool enough not to run the fans. There is a fix around this that you can get from zzperformance. its called an 'e stat' and it work real well, I use it with my 160* tstat and have had no troubles with it.
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Old 08-05-2005, 07:12 PM   #5
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PDad...we were both off a little. Trying to supply the best info. so out comes the book.

From the 97 FSM
While in low speed operation the circuit supplies the right side cooling fan motor, the left side cooling fan motor is supplied a feed through a resistor causing it to run at low speed. When high speed operation is commanded the right side fan continues to run at low speed, but circuit B supplies a feed directly to the left side cooling fan motor causing it to run at high speed.

PCM commands low speed fans operation when the following conditions are met:
- Vehicle speed is less than 58 mph
- Engine coolant temperature is above 100 C / 212 F
OR
- Vehicle speed is less than 40 mph
- Intake air temp is above 9 C / 48 F
- A/C refrigerant pressure is greater than 190 psi

High speed is commanded when the following conditions are met:
- Vehicle speed is less than 65 mph
- Engine coolant is above 108 C / 226 F
OR
- Vehicle speed is less than 50 mph
- A/C refrigerant pressure is above 260 psi

So basically from the book even if you are over 226 F your fans shut off once you reach 65 mph. Which makes sense because at that point you are most likely getting more airflow from speed then the fans can deliver.
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Old 08-06-2005, 08:18 AM   #6
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The 2000+ Bonnevilles utilize the series/parallel lash up via relays to operate the cooling fans in slow/fast respectively. Not sure about the 96-99'*, but I think you're right on the money with the resisters being inserted for slow speed ops, Bill.
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Old 08-08-2005, 03:11 PM   #7
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Thanks guys for the information !!
Should be no problem to fix now.

Bob
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