Cooling fan issues

[caprikid]

Hi

I have a 1.6 16v Astra Artic. Recently the engine has been getting hot in standing traffic. I assumed this was an issue with the fan. I therefore removed the plug from the sensor on the back of the radiator and used a paperclip to connect two terminals. When doing this, the fan spins literally about once and then stops and will not turn again, no matter how much I wiggle the clip. The plug is of the two pin type, so I assume single speed fan. I then removed the cooling fan and bench tested it and it works fine. I assume that this must be some kind of electrical fault rather than a temperature sensor issue given that it only spins once? I'm not great with electrics (but keen to learn). I have access to a multimeter and have the wiring diagrams in the Haynes manual. I was just wondering if anyone had any general pointers for diagnosing the issue, can think of anything else I may have missed or whether there are any common issues that may cause this. Thanks in advance Mark

 

[Mr.Negative]

it's not a sensor, it's a thermostatic switch that makes a connection when a certain temp is exceeded.

If you were to bridge the pins in the connector (rather than the thermostatic switch that is screwed into your radiator) and it runs then it would suggest it's the thermostatic switch at fault.

 

[Mr.Negative]

I believe you will also need the ignition on to test bridging the pins too.

 

[MrBird]

I concur, if the fan runs fine on tbe bench.
I have a spare new thermo switch, yours for tbe postage.

Fitted a new radiator and orderd the switch just in case.

 

[caprikid]

it's not a sensor, it's a thermostatic switch that makes a connection when a certain temp is exceeded.

If you were to bridge the pins in the connector (rather than the thermostatic switch that is screwed into your radiator) and it runs then it would suggest it's the thermostatic switch at fault.

Hi Thanks for the reply. My mistake regarding it being a switch. When I do this (bridge the pins in the plug), the fan runs for a second and then stops but the fan itself runs fine on the bench. This is what made me think the switch was not the culprit but some electrical issue. Do you think it may be worth changing the switch initially as a precaution?

 

[caprikid]

I concur, if the fan runs fine on tbe bench.
I have a spare new thermo switch, yours for tbe postage.

Fitted a new radiator and orderd the switch just in case.View attachment 21962View attachment 21963

That's really kind of you thank you for your offer. Do you mind letting me know details for doing this? I am still slightly concerned about the fact that on the car the fan runs for a brief second only when I bridge the switch rather than continuously which is what made me dismiss the switch in the first place but I guess it's worth replacing to eliminate this as a possibility. Thanks again both of you for your help and for replying so quickly. I really appreciate it

 

[MrBird]

I seem to remember that you can put the switch in boiling water and the resistance changes

 

[Mr.Negative]

Hi Thanks for the reply. My mistake regarding it being a switch. When I do this (bridge the pins in the plug), the fan runs for a second and then stops but the fan itself runs fine on the bench. This is what made me think the switch was not the culprit but some electrical issue. Do you think it may be worth changing the switch initially as a precaution?

hmm... ok. if it's the plug (not the switch that's screwed into your rad) and it runs the fans for only a second it sounds like a relay at fault? (that's if they run a relay? ) mines been messed around with (by me) and I cant remember if it is through a relay so need to find out if they do (cant remember).... you need to find out if the fan is controlled through a relay and then you're best swapping for a good known working one to test..... usually 4 pins on a relay (low voltage/signal side & high voltage/ampage side) you can also bridging the high ampage side (will be the two thicker wires into the relay) to test but be warned! - if you do try to test relay by bridging use thick gauge wire and watch out for sparks! far from ideal way.

 

[Andy Ramdidin]

From what you say, ie fan spins briefly when thermoswitch plug terminals are shorted, it does sound a 90% certainty that the fan's relay is at fault. Sounds like the relay contacts are bouncing open after briefly closing. You will have to find the location of the relay, most likely under the bonnet in a black box with other electrical relays, or possibly it could be under the dashboard in or near the fuses panel. Once you've located the relay, quickest thing to do would be replace it with a new relay. Whilst you're looking at the fuses, you might want to replace the fan fuse. Weird things, like oxidation of fuse terminals, can happen.