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Mark, ASE Certified Technician
Category: Buick
Satisfied Customers: 847
Experience:  34+ yrs Dealership Exp. - Fully State & ASE Certified - GM Master & GM World Class Tech
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96 buick century: wont runs..runs good..highway

Resolved Question:

Hi, I have a 96 buick century with a 3.1 . The electric fan works when it wants to the temp gage goes to three quarters when idling and the fan won't come on . The car runs good and the temp gage stays about half to a quarter on the highway. I put a jumper wire on the fan it works fine ,and replaced the fan sensor on the firewall. Randy.
Submitted: 6 years ago.
Category: Buick
Expert:  Mark replied 6 years ago.
Greetings, my name is Mark.

Do you have 1 or 2 cooling fans?

You keep mentioning "cooling fan" and according to my diagnostics, I am showing 2 cooling fans.

Let me know.............
Customer: replied 6 years ago.
HI Mark ,sorry didn't realize thare was a fan on the outside of the radiator I was just looking at the one on motor side of the radiator I didn't hear any fan so I assume the other fan isn't working but I didn't check it. Randy
Expert:  Mark replied 6 years ago.
Okay, .... No problem on this end. Just didn't want to give you the wrong diagnostics.

As far as "hard" failures go, the computer is the main brain of the whole system. It controls the relays that control the fans. I think there are 3 relays and the computer.

The big factor here is wiring. Open wires, shorted, or grounded. I don't know what kind of experience you have, but finding wiring issues can be tricky. You could start by just replacing the 3 cooling fan relays, and if that doesn't fix it, then you know you either have a wiring issue or a bad computer. We (I) have seen both in the field.

There is a coolant sensor in the lower intake, but the reading goes to the computer and the computer turns the fans on based on the reading.

I do realize you said that when you drive down the road things are okay. And I know you understand that the air flow across the radiator dissipates the heat and you're okay. However, if you do have any cooling issues, it is magnified at an idle. If the radiator is partially plugged with sand or debris, it is going to show up more prominently at an idle.

But I do read where you say when the fans come on, it's okay. I only mention this to make sure we cover all the bases. Water boils at 212 and you gain 2 degrees per pound on the radiator cap. Add 16 degrees and now water is boiling at 238 or 240 range. Now make it coolant, and you raised that up to about 275 or 280 depending on your concentration.

Your cooling fans should come on anywheres between 224 - 228. And then shut off around 200 or so.

I have included a "flow-type" chart diagnostics for your cooling fans. It has the schematic, some description. The file is in a WORD format. CLICK HERE to view the file. Let me know if you have trouble viewing.

The diagnostics do call for some special tools to diagnose. I thought you could read the chart, and maybe it will give you some ideas.
Customer: replied 6 years ago.
I will try to replace the three relays could you tell me exactly where thay are located, if that doesn't work I will replace the coolant sensor and could you tell me exactly where that is located .Thanks Randy.
Expert:  Mark replied 6 years ago.
Your coolant sensor is screwed into the lower intake. Follow the upper radiator hose to the engine. You'll see a "two-wire" connector into a little brass sensor. Takes a 3/4" (I think) wrench. You might have to remove the throttle body to gain access.

Your relays are on what they are calling the "Underhood Accessory Wiring Junction Block" and that is located on the right side of the engine compartment on the strut tower.

Picture below is an "upside" down view of the junction block. You should see a cover on the black box. The cover should have a component "legion" telling you what is what.

Underhood Accessory Wiring Junction Block

Object Number: 399300  Size: LF

Edited by Mark on 8/22/2010 at 6:27 PM EST
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