Thread: radiator fan problem

My temp gauge has always ran around 160-180. The other day it was up around 200. I opened the hood and noticed the fans were not running. I figured it was the coolant temp sensor. Replaced that but no change. Also replaced the 5 pin fan relay.Nothing. I unplugged the short harness from the sensor and the fans run. When I plug it back in, the fans stop. I would think they would stop when there is no power going to them or is there another source? Any help is appreciated.

replace coolant temp sensor on the manifold cause it feed the gauge in the dash

Do you mean the sending unit for the gauge?

I have looked all over for a sending unit. I have a Haynes manual and it shows th early 3800 but not the Gen II. There is nothing on the front of the motor like it says. This book doesn't show much as far as the 98 motor goes.

I'll try a thermostat tomorrow. This car has never gone past 180 until the other day. All of my cars are 89 and older, so this is new for me. I appreciate all of the suggestions though. Let you know what happens.

I'm putting the thermostat in today. Is there any special way to put the antifreeze in? Do I have to bleed the system?

Installed the thermostat. No change. Unplug harness to sensor, fans go on. Plug it in, they go off. Could it be that the new temp sensor is defective? I have seen it happen.

BB37 Sure. It's a 1998 Grand Prix GT. 3800 Gen II. No mods. So I take it that the gauge should go to 200 degrees before the fans go on? We just bought the car 2 months ago. Should the fans run when the key is off? As I said, I'm unfamiliar with the newer stuff. I have a 71 Torino wagon and a 65 Chevy Van. Newest is an 89 S-10 pickup. The GrandPrix is very cool. I've always liked that body style. Thanks, Crow.

Obviously I have a lot to learn about this car. The car runs steady at 200-210 degrees now. The gauge must have been reading incorrectly. Drove it around for about 50 miles and never overheated. Also, had a noise I thought was an alternator bearing going bad. Removed the belt and saw that the idler pulley was missing. That's right,Gone. Only the bearing was there. and that was locking up and turning purple. Put a new pulley and belt on and all in good again. Love this car.