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Hi all hope you're all doing well. I have a 2003 convertible beetle 2.0. So far have replace the y shaped cooling flange that blew out, water pump, timing belt, plugs, coil pack, overflow reservoir, and ECT sensor. I am still having issues with the car getting hot so I decided to run a flush/cleaner through the cooling system in case I had any blockages. While I was running the engine for the 20 minutes with the flush in I noticed that the cooling fans were not kicking on and never did. So I turned on the ac to see if they would still auto kick on with the AC and they did taking the temps back down. But I'm wondering where to start with figuring out why they wouldn't come on normally. So far my thoughts are maybe thermostat is stuck closed so the radiator fan switch is not triggering or the radiator fan switch sensor is bad. What do you guys think maybe a fuse or relay? I know I had to replace the coil pack because it got soaked when the flange blew out. Any advice appreciated. Thank you.
 

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Actually thinking about it it's probably not the thermostat given that it started cooling off when the cooling fan kicked on with the AC. So confused!
 

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After a cooling system service; it is not uncommon, to have air pockets in the block and this, can cause a overheating with the cooling fans not coming on. Normally, you should replace the thermostat; when, doing cooling system repairs. The thermostat on these VW's, do NOT; have little jiggle/bleeder valve, that lets coolant in, from the block to the radiator hose. So, some people, drill a small hole; in the thermostat, to make burping, purging the air out of the system easier. The service manual, recommends the use of the vacuum fill too; which, elminates all air out of the cooling system but not everyone has a tool like this.

Check out this video: going over burping of the system techniques, info on drilling the hole in the thermostat and checking for blockages, from the return hose, to the coolant bottle.




thermostat replacement; drilling hole:


 

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Thank you I'll go ahead with the thermostat then. Do you think it could be the switch as well?
 

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The fans are turned on automatically in two ways ; the temperature sensor by the firewall via the FCM and the temperature sensor mounted on the radiator bottom left. The A/c button also turns them on via the fcm but not automatically.
 

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So if it's no coming on automatically without the AC it must be a problem with either the radiator sensor or the sensor is not getting hot enough because of the thermostat not opening up
 

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Smiley is there a probe kit you would recommend that I could use for jumping pin in the connectors together? I'm not super familiar with electrical so it's not something I've picked up for my tool kit yet.
 

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So if it's no coming on automatically without the AC it must be a problem with either the radiator sensor or the sensor is not getting hot enough because of the thermostat not opening up
Kinda like the other way around, if the thermostat stays slightly open the coolant at the radiator doesnt' get hot enough to turn the fans on via the sensor mounted on the radiator, but if the coolant is hot enough in the engine block it should turn fans on with the sensor mounted on the coolant flange by the firewall via the FCM.
 
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