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Registered
1986 Deville Sedan 4.1 V8
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14 Posts
Discussion Starter #1
Hi everyone, just a question with regards to my Cooling fans which I think are not kicking in.

I have changed both the Relay and Temperature Switch and did the check to confirm the both motors are OK by bypassing the relay, the fans run fine. As I am always cautions when a car has no temperature gauge only a light I have fitted my own gauge which is the old style reading all the time. According to this the temperature will reach well over a 100 degrees but there is NO sign of the fans kicking in, checking the codes and there are No faults found on the system.

1. At what temperature should these fans kick in.
2. Can I wire a bypass switch in to work in conjunction with the current standard set up as a few people have said to me not to tamper or change anything with the electrics on these cars.

Thanks in advance for any help as its now driving me nuts finding the issue.
 

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2004 Deville
2004 Deville, Silver, Gone, but not forgotten, 1972 Eldorado, 1974 eldorado, 1975 CDV
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645 Posts
Someone please correct me if i'm wrong, but if i am not mistaken the fans will kick on at around 210-215 degrees and shut off at about 195. You could wire a switch from the fan relay and mount it on the dash somewhere, that's what i did with one of my firebirds.
 

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Super Moderator
White Diamond '03 DHS (with DTS floor shift)
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86,575 Posts
Sounds to me like you are over thinking this. Not sure what temperature the fans activate on the 4.1, but the normal operating temperature should be around 200°. You have not mentioned anything of any concern. If you are not overheating, things are most likely operating as designed.

If you want to check the fan operation, I think, even on an '86, the fans came on when A/C is selected. Turn on the A/C (or defroster) and then check to see if then fans are running.
 

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Registered
1986 Deville Sedan 4.1 V8
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14 Posts
Discussion Starter #4
200 degrees Fahrenheit is around 93 degrees centigrade which is what my gauge reads in but it goes well over to around 230 degrees Fahrenheit making me think they are not kicking in. I don't use the car much over the winter months and as it get pretty cold here they don't kick in as much as during the summer months obviously. Me just being over cautions as a mechanic but is there a way to fit a bypass switch in the circuit just a fail safe and put my mind at rest. Thanks.
 

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Super Moderator
White Diamond '03 DHS (with DTS floor shift)
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86,575 Posts
I'm sure it is possible to wire in an override switch, but it should not be needed if everything else is in good shape. I think you first need to figure out why you are getting up to 230°. A fan override would be a bandage, and most likely a temporary one.
 

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Registered
1985 Fleetwood 75
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345 Posts
I believe on your car fans are controlled by a fan control module that is attached behind front left headlamp. This is a variable speed fan control module connected to the body control module. BCM has firmware that has a programmed on temperature for fans. I believe starts fans turning about 110*C full one about 130*C and off about 95*C. Thermostat these motors about 95*C opens. Motors are run hot for emissions that is why oil cooler. Temp sensor on motor feeds BCM a temp value converted to coolant temperature in bcm, also senses the AC liquid line when working will also turn on fans about 57*C.
You can test fan circuit with on board diagnostics. Hold Warm and off buttons together about 3 seconds on HVAC controls, display goes to segment test then displays codes then to .70 waiting for commands. Press the defrost button next to auto should then display F8 for fan testing mode hold the fan high button down and fans should start turning on all the way up to full speed. This confirms BCM has full control of the coolant fan circuit. If problem it is probably the fan controller behind headlight, needs new mosfet transistors. Note case heat-sink is live so do not short heat-sink to ground.
BCM firmware versions have programming for coolant fan on and off temperatures. Motor temp and ac freon liquid temp.
Use bcm diagnostics to confirm all your temperature sensor inputs are reading ambient temperatures.motor temp sender has fail problems due to connectors or wiring to bcm.
The relay you talk about only enables the circuit when key is put to run position. I think later models went to a 3 relay type fan control circuit with fans put in a series parallel combination circuit for two level speeds. Look behind headlamp due you have this module.
Use the diagnostics to do the tests.
An external temp analog gauge is smart move as overheating is not good for these motors. whc cad put idiot lights for such high end cars who knows.
Temp also controls when motor goes closed loop >70*C for o2 sensor operation and when transmission torque convert will use lockup.
 
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