[AcesUp]

I think it might be bad.

[335NJ]

Any codes?

[AcesUp]

I haven't brought my laptop down to check. I will in a minute.

When replacing the sensor, is it necessary to fill and bleed the coolant as this DIY states?

http://www.pelicanparts.com/BMW/tech..._Replacing.htm

[dmatre]

If the fan goes full-tilt for no reason, 99% of the time it's 'cause the water pump bought the farm - not due to a faulty sensor. Check your codes soon or you'll be walking home tomorrow.

[fazman]

Originally Posted by AcesUp

My radiator fan just started going full blast a few minutes after start up, while engine is cold. I found this temp sensor at the local pep boys:

http://www.pepboys.com/product/details/9814581/01072

I'm going to pick it up now as I need the car for tomorrow. Will I need any special tools to replace this?

if your near the long island area i'll check your codes for free, more than likely you have a failing waterpump and/or tstat. get it taken care of asap. start with checking your coolant level.

['02onthebrain]

That is the coolant temp sensor in the engine block, but as others have said it is likely not your problem. Your thermostat and waterpump are probably on the way out. You will likely get a P0128 code next for coolant temp too low because the t-stat will stick open.

I just chased this issue down on my 335xi and ended up replacing the waterpump, t-stat, radiator, expansion tank cap and the coolant temp sensor.

But to answer your original question, you just need a deep socket to replace the temp sensor in the block. If you are quick, you can unscrew it without losing too much coolant and swap the new one in. Don't over-tighten because you can snap the head off. Just enough to snug it up. Check the coolant level and bleed the system if you are concerned with any air getting in.