Why are the fans not working right

PATRICIA FANT

MEMBER
2003 MAZDA 6
3.0L
V6
MANUAL
192,000 MILES

The car started running hot. We found out that the fans were not working and the radiator had a hole in it. So we replaced them both with brand new ones and a new module that connects to the fans.(A little black box) It worked perfect for two weeks then the fans stopped working and it wanted to run hot. So we replaced the coolant temperature sensor and it ran on all day. But now the fans are not working again and we stopped at a red light and the temperature gauge went up 3/4 of the way. But it is fine if we are going down the road. So what else could it be?

1 Reply

STEVE W.

MECHANIC
12,962 POSTS

Going down the road the airflow is enough to keep the engine cool. It sounds like you need to find a shop with a good scan tool that can control the fans and test to see if the PCM has a problem and work out from there.
Check the wiring and power supplies to both fans. Fuses can look good but be blown. The contacts in the relay housings and fuse box can get hot and weaken so they no longer make contact.
As you had a coolant leak that may have gotten into a connector and corroded it or the wiring may have loose or broken internal wires.

I would start by testing the fans with power to be sure that they are still okay.
Then use a scan tool to look at the coolant temperature reported by the sensors. The fans turn on when the coolant is over 203 degrees, or if you turn on the AC.