overheat one day, fine the next

[Jasminka]

Yesterday I was cruising down the highway, noticed the temp guage was almost at the H mark, so pulled over. We lifted the bonnet, the overflow container is half full and the serpentine belt is there. Ambient temperature was 30 at the most. So walked down to nearby coffee shop and had lunch. Came back to the car, no sign of coolant leaks. Then chose a route home with no hills and fewest traffic lights. The temperature guage got up to 3/4 (it is normally at half). Checked it over again this morning and took it for a drive. It behaved itself - only got up to halfway.
So, is this a sticky thermostat?

 

[fxxxrr]

i find that my level in the radiator seems to drop after a hot drive, eventually it get slow and car runs hotter than i like it to,

i would check your actual level in the radiator

 

[deserthead]

Air bubble in your cooling galleries, more then likely. How long since the last flush?
I would check that first and if all good, then I would be considering the temp sender sensor might be stuffed. There are 2 on the VS, one for the ECU and one for the gauge. Your gauge one might be on the way out.

 

[VT&VX]

How old are your hoses?
Have you recently replaced a hose with a faulty one?
Has that new silicon hose lost a layer and now it is travelling through your cooling system?

Try removing the thermostat when you flush the cooling system. Drive around without the thermostat for a week. Check the thermostat by putting it in a tin can of boiling water on stove top. Check it opens and closes when it is supposed to.