Hi,  for no reason my 2001 v6 3ltr has developed what looks like an airlock eg, water bubbling/rising up /down in expansion tank, car has had no problems and I parked it up for few weeks in the cold/snowy weather we have had, and one sunny/warmer day I decided to start the car to keep battery charged, and it started immediately with no noises etc, but it started to overheat and boil in the expansion tank it had water in with antifreeze and wasn' frozen, I have since noticed the heating in car is barely warm ? Making me think it's an airlock ?, sometimes if I rev upto 2000revs the temp gauge goes back down to normal, then I let it idle and it goes back to maximum/overheating, the fans come in very quickly from cold start, but do not obviously cool engine down enough to cool engine and then stay running all the time until just after I turn engine off. I have not driven the car since this problem started only run on tickover. Thanks for reading.  Colin 

Hi Colin

I would first check the coolant pressure cap as if this goes faulty and allows the system to lose pressure then the boiling point of the coolant will be lowered which leads to overheating.

Also, it can in certain circumstances allow air to enter the system, again leading to overheating and also poor circulation of the coolant

Also, its the cheapest and easiest part to replace, so I would definitely start there.

Let us know what you find

Cheers .  Trevor