Hello After a few weeks of looking around on different site's for my problem and coming up with nothing, I have had to come begging for some experienced wise words!! The car in question in a Range Rover Sport Tdv8 2008 with 128000 miles on the clock. I have owned the car for around 19 month now and all has been running well and really enjoying the car..... BUT i was driving the car the other week and the temp gauge shot up to over heating for the first time since owning the car. I turned the car off straight away and let it cool down. when i checked the coolant level it was empty i was wondering where it had all gone and i originally thought head gasket as there was no leaks from under the car. I filled the car up and got it to a garage and it didnt over heat but lost some coolant. Once at the garage he filled and bled the cooling system but I am getting water flow back through the return pipe into my expansion tank which looks like bubbles which worried us more to head gasket. He pressure tested the system sniff tested and all come back normal so he was happy it isnt the head. I then fitted a new housing which includes the temp sensor and thermostat in case this was causing an affect on the system, while i had the car apart i decided to change the expansion tank for a new one because when I got to it the wire from a previous owner had been cut and hard wired so the coolant low level never come on the dash so I got that back working. I bled the car back up following a procedure i found on one of the forums it was all looking fine with still a return flow from my top pipe into expansion tank it held its coolant on the drive up to temp and produced warm air out the heater indicating it was flowing round the system correctly telling my the water pump is working correctly. so this is where my problem is when cold my car is telling me it has sufficient coolant fluid level just under max. when i start the car its stays at that lever for a short period of time than then disappears pretty quick i am guessing when the thermostat opens. The top hose for the radiator is pressuring the return pipe is flowing into the empty expansion tank and telling me low coolant on the dash, which there is no coolant in the tank between min and max I can just see a bit at the bottom. when i turn the engine off and let it cool down the expansion tank gradually gets the coolant level back to the correct level just under max once it is at a certain temperature. Why is this happening? what would cause it? anything i could look at doing?

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could be air in the system. i think it was a good idea to change the expasion tank, but if there's air, it needs to come out. might happen over time. keep the cooling level on max when cold RRS 3.0 SDV6 HSE Lux
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it does sound as if you have a air lock in the car as you have run it down do a search on here or the sister site disco3 even though they dont have tdv8's in them they have very knowledgeable people as wellthen search how to bleed the coolant as they are not that easy to get right