Hi guys, I’ve got a stock 05 WRX Wagon (well it has a cone filter and Prodrive exhaust but no map or anything) and if I sit on the motorway the temp gauge sits up at the line before scary heat, and equally if I give it some hard acceleration it gets hot pretty quick.

Just wondering if my potentially old and crappy Cone air filter is to blame or something else?

any advice much appreciated 

It's not your crappy cone filter, I would guess its more likely to be your water pump over time impellers wear down reducing the flow rate as the water isn't circulating as fast the system is unable to cope with higher temps under load  

or the cooling system could just need a flush which is where I'd start first.

 

That sounds like it could be just it! Thank you very much, will get that looked in to.