Good evening

I bought a 2007 Sport HSE 2.7 about two months and noticed it was using coolant (couldn’t see a visual leak).

It went to the dealer and they initially replaced an o-ring on the oil cooler. A week later, same problem, this time they replaced the oil cooler housing. I’m now facing the same issue again and wondered what could the issue be?

The coolant is lasting around a week, no visual leek. No coolant in the oil. I’m not sure if it’s helpful but once I top the coolant back up the heaters inside blow hot (selected 26 degrees) for around 5 minutes and then it’s just Luke warm air after that.

Take it back to where you bought it (if not private) and get them to repair it. They have to by law.

Hi, I'd be tempted to put a die in the coolent, if it's only lasting a week you would soon be sure of where the leak is. Then go back to who repaired it and show them where the leak really is, assuming it was misdiagnosed but being really polite about it.
I'm pretty sure you can but fluorescent die specifically for this.

You can also get pressure testers off eBay to pressurise the coolant and then you should see where it’s leaking from.

Maybe £20