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[catera00]

Hi, I have a 2000 Cadillac Catera (America obviously). This is my first post here but I've gotten a lot of good info from this forum already.

So heres my question:

My cooling fans usually start up when my temp gauge gets to one line above the halfway mark. This will bring the temp back down.  But sometimes the fans dont start till it gets in the red, overheating area of the gauge. So now the red temp light comes on and the fans start and the temp goes immediately back to normal.  I know there are 2 sensors in the radiator. Are they responsible for turning those fans on?


I'm just trying to figure out why the fans are waiting so long to start cooling the engine. They should start before it gets overheated.  Thanks for any help!

[TheBoy]

If same as UK cars, there are temp switches in the rad. On UK petrol cars, this is a single dual temp switch mounted in rad just under top hose.

Does that make sense?

[catera00]

If same as UK cars, there are temp switches in the rad. On UK petrol cars, this is a single dual temp switch mounted in rad just under top hose.

Does that make sense?

Yeah I've sen that sensor. There is one under the top radiator hose and one below it on the bottom of the radiator. Does it decide when the fans come on? Does dual temp mean it turns on the fans at 2 different temps? Like 1: when it needs to cool down a little and 2: when its overheating? Thanks for the quick response.

[TheBoy]

If same as UK cars, there are temp switches in the rad. On UK petrol cars, this is a single dual temp switch mounted in rad just under top hose.

Does that make sense?

Yeah I've sen that sensor. There is one under the top radiator hose and one below it on the bottom of the radiator. Does it decide when the fans come on? Does dual temp mean it turns on the fans at 2 different temps? Like 1: when it needs to cool down a little and 2: when its overheating? Thanks for the quick response.

There are 2 temps, on UK petrols, its a single 3 pin sensor, on other cars it may be 2 seperate sensors.

Again, on UK cars, the first setting is just above normal running temp, turns on fans at lowish speed. As temp approaches 100C (212F), it turns on fans at high speed.

From memory, these are normally open, so bridging with a paperclip will prove fan motors, relays and fuses.  Slow speed fans can remain on with ign off, but I think high speed fans need ign on.

I have some UK wiring diags if you need to delve further

[catera00]

If same as UK cars, there are temp switches in the rad. On UK petrol cars, this is a single dual temp switch mounted in rad just under top hose.

Does that make sense?

Yeah I've sen that sensor. There is one under the top radiator hose and one below it on the bottom of the radiator. Does it decide when the fans come on? Does dual temp mean it turns on the fans at 2 different temps? Like 1: when it needs to cool down a little and 2: when its overheating? Thanks for the quick response.

There are 2 temps, on UK petrols, its a single 3 pin sensor, on other cars it may be 2 seperate sensors.

Again, on UK cars, the first setting is just above normal running temp, turns on fans at lowish speed. As temp approaches 100C (212F), it turns on fans at high speed.

From memory, these are normally open, so bridging with a paperclip will prove fan motors, relays and fuses.  Slow speed fans can remain on with ign off, but I think high speed fans need ign on.

I have some UK wiring diags if you need to delve further

Actually that answers my question because that would explain why it only turns on when the temp gets very high. Its not turning on when temp goes a bit over normal. So thats the malfunction. I just need to make sure I get the correct sensor now. I assume one is for low temp and one is for high temp. Ones on top of the radiator under the top hose, and the second is about 12" or so lower than the first. Thank you very much!

[catera00]

on second thought, do you think my problem is with the temp sensor or could it be the relay that it triggers?

This is an excerpt from an article I read about the car's cooling system:

100°C (212°F)
The primary fan is energized at low speed using a resistor; the secondary fans are energized in a series (half speed).

105°C (221°F)
The primary fan is still energized at low speed; the secondary fans are switched to full speed.

110°C (230°F)
The primary and secondary fans are at full speed.

[TheBoy]

on uk cars, we have slow speed (fans in series) and high speed (fans in parallel).

Playing about bridging the sensors will show which one does what

[Andy B]

on second thought, do you think my problem is with the temp sensor or could it be the relay that it triggers?

This is an excerpt from an article I read about the car's cooling system:

100°C (212°F)
The primary fan is energized at low speed using a resistor; the secondary fans are energized in a series (half speed).

105°C (221°F)
The primary fan is still energized at low speed; the secondary fans are switched to full speed.

110°C (230°F)
The primary and secondary fans are at full speed.

A certain Terry Wong on the Yahoo Catera group has the bridge connections for the purple test point in the fuse/relay box under the bonnet/hood. It shows which connections to bridge & which fan(s) should run and at what speed.

[catera00]

ok I'll check it out. Thanks again