VX Random 3 monthly overheat

[G200Sleepr]

Hi All, I'm only new here but have a question. I have a 3.8L VX. And starting about a year ago, it would just randomly "overheat" for no known reason. It has only done it 3 times ever, the temp gauge will read normal for about 20 mins then suddenly skyrocket to the computer going HOT HOT HOT in about 30 seconds. Only once when I have pulled up has there been any water run out from under the car. Once the car is restarted it is fine and doesn't do it again for a long time. I have tried replacing the thermostat and coolant; There is pressure in my hoses. The only thing I have found is that all three times the heater has been on to some degree. I would think this to be suggestive, however the heater gets used by my partner on almost a daily basis with no troubles. The vehicle has done many highway trips without a single issue and is a daily driver. Anyone who has experienced this before and/or has some suggestions it would be greatly appreciated.
Cheers, Dave

[accentstencil]

It happened to me once and it was due to a bad connection at the plug for the cooling fans, where they plug into the loom. Were your fans on at the time of overheating?

[VYMAD]

It happened to me once and it was due to a bad connection at the plug for the cooling fans, where they plug into the loom. Were you fans on at the time of overheating?

Try this and if that fails, make sure that the cooling system's been air bled properly. Sorry but I have no other suggestions. I take it that the coolant reservoir is at its correct level and raddy full?

[Simonn]

could also be that your cooling system is blocked doubt it though usally only happens to older cars.

[G200Sleepr]

Hi Guys,
Thanks for the responses. Yes my cooling fans are both on and functional. However I will check that again, better to be safe than sorry, right?

I have also checked the coolant and radiator levels, and no probs there, also been bled to the best of my abilities.
Holden suggests maybe an airlock in the heater assembly.
Ah well, its due for new hoses and coolant. I think I shall just let them do their deeds and they will tell me if they come across anything while they are in there. Then it becomes a service warranty job
Thanks for your help all. Dave.