2001 Lumina 3.1 cooling fans don't work

Hi folks, here's my situation

I just bought a 2001 Lumina, 142,500 miles. It has an overheating problem.

Here's the problem -

The two cooling fans that do not engage at any temperature. A/C on or off does not matter. They just don't run.
(It has been near 100 degrees here, and the engine does warm up quickly).

Engine cools fine on the interstate (ram air cooling) but overheats in normal city (stop and go) traffic when the air flow is low. Blows coolant from the reservoir tank. Swallows it from the tank, so I know it's getting coolant both ways. (Radiator cap should be fine.

I switched #1 cooling fan relay with the ignition and the car started fine. Removed the relay for #2 and no effect. No burn marks on any of the relays or connectors. They're good.

Both fans spin freely, but I haven't hot-wired them (yet) to see if they'll run directly. While I'm not surprised to see one fan go bad, two seems odd.

Coolant boils out of the overflow tank when it stops. Otherwise, no other related issues.

To date, I have replaced -

Coolant temp sensor (on the thermostat housing. Not sure if there is another one.
Oil pressure switch
Serpentine belt

What I have not checked -

electrical current to the fans. My guess is both fans are good.

Any good ideas are welcome!

Thanks!

I've got the same issue with my 91.
Does yours get hard to start when it's been sitting off a while (like 30-90mins?)
if you unplug the coolant temp switch, it should start the fans when you turn the ignition on, if your 3100 is like my 3.1. I know I've got power and the motors are good.

Cooling fans should go on at 221 or with the ac, How hot does it get, a bad cap can cause after boil into the coolant jar, many things can cause a true overheat condition , on that engine coolant sludging or head gaskets with old Dexcool are the most common causes.

I replaced my rad cap 2 months ago, because I thought it might have been that, so it wasn't getting the pressure it needed. I even did a coolant flush, to make sure what i had in was good.

In the similar threads just below, I noticed this thread http://www.automotiveforums.com/vbulletin/showthread.php?t=949864 where one message said
All GM W-cars wait on a/c head pressure to turn on the fan(s) at 175 psi the primary fan comes on, and at about 250 head the secondary comes on....
My A/C hasn't worked since we had the car, and even turning the switch on does nothing. I'm about ready to put a manual switch in, to turn the fans on myself.

No problems like that. I just put a manual switch in tonight but plan to find the problem when I have more time.
Yours sounds more like a coolant temp sensor.

I've got the same issue with my 91.
Does yours get hard to start when it's been sitting off a while (like 30-90mins?)
if you unplug the coolant temp switch, it should start the fans when you turn the ignition on, if your 3100 is like my 3.1. I know I've got power and the motors are good.

Thanks, I'll check that one out. My AC works fine. Since I had the hood open, I checked the vacuum lines. The one by the battery is now replaced, it broke apart in my hands.

Manual switch is a good idea, definitely DO put a fuse on it. 30 amp should be more than sufficient. I'm using 16 gauge wire for mine for the time being.

Getting a new radiator cap tomorrow anyway. I don't know how long the current one has been there.


I replaced my rad cap 2 months ago, because I thought it might have been that, so it wasn't getting the pressure it needed. I even did a coolant flush, to make sure what i had in was good.

In the similar threads just below, I noticed this thread http://www.automotiveforums.com/vbulletin/showthread.php?t=949864 where one message said

My A/C hasn't worked since we had the car, and even turning the switch on does nothing. I'm about ready to put a manual switch in, to turn the fans on myself.

Yesterday, it got hot enough for the overheat light to turn on. I was able to cool it some by using the interior fan set on high heat. Way comfy at 95 F outside. lol

At no time did the cooling fans turn on. Engine temp hit the red line in city traffic but was fine on the highway.

I'm getting a new cap tomorrow. Not sure how long the current one has been there but it wouldn't surprise me if it were the original.

Any suggestions on getting the sludging out?

Thanks!

Cooling fans should go on at 221 or with the ac, How hot does it get, a bad cap can cause after boil into the coolant jar, many things can cause a true overheat condition , on that engine coolant sludging or head gaskets with old Dexcool are the most common causes.

No problems like that. I just put a manual switch in tonight but plan to find the problem when I have more time.
Yours sounds more like a coolant temp sensor.

I replaced the temp sensor about 3 months ago. made no difference.