Is this thermostat?

I am a new owner of a BMW x5
I too have experienced the no heat in car, I was out the other day and thermometer flew into red after only driving 25 mins
I stopped turned off engine started up again and all was ok
My mechanic has said it's defo the thermostat....however on going in the engine discovered under the rocker cover cap was White milky residue under cap.....not used any extra water and dipstick oil is clear.....I called the garage I bought from and he fully assured me it is a common fault on these engines E53 3litrei and he says that there is a conversion for the rocker cover breather pipe, and said no way was it the head gasket!!!!!!!! And also he said that problem only seems to happen on cars under 100k mines only done 73k
I am new to BMW so can't say either way.....as normally these indicators as already suggested are head gasket....I do have this car under warranty so he knows if it went pear shaped!!!!!what would happen
Hope this helps!!!!! With any similar faults / answers

Help us help you better by giving us some details/information about which of the multiple X5 models you have. There are multiple engines & transmissions etc...and you have no signature with vehicle details...nor did you mention anything about which X5 model/model year/build date your vehicle is.

• 3.0i (m54)
• 3.0d (m57)
• 4.4i (m62TU)
• 4.6is (m62TU)
• 3.0d (m57n)
• 4.4i (n62)
• 4.8is (n62)

Thank you
sorry its a 2002 X5 3.0LITRE I PETROL as i put (E53) I thought
thanks again

It seems like you have air trapped in your cooling system. I'd check the coolant level and bleed the system first.