Heat issues in '16 Tiguan

[Call.me]

My 2016 Tiguan, the engine temperature climbs up during longer drives, especially when I'm going uphill or idling in traffic and inside the cabin, the temperature can be very inconsistent, I've already checked the coolant level and the radiator is fine, random chat with a colleague revealed something about a heater core, I'm honestly kind of new to cars, this is my first, so do I have to replace this heater core thing or is it something I can just get my brother to work his hands around?
Asking here coz I need second and third opinions , the last time I took a colleague's word for it , I ended up spending $100 more than I should have

 

[riri19]

Yeah could be the heater core or the thermostat. The heater core isn't easy to replace and usually needs some dashboard work, so unless your brother's pretty handy with cars, it's better to get an expert to check it first. That way you avoid spending extra on the wrong fix.

 

[CometHunter]

My 2016 Tiguan, the engine temperature climbs up during longer drives, especially when I'm going uphill or idling in traffic and inside the cabin, the temperature can be very inconsistent, I've already checked the coolant level and the radiator is fine, random chat with a colleague revealed something about a heater core, I'm honestly kind of new to cars, this is my first, so do I have to replace this heater core thing or is it something I can just get my brother to work his hands around?
Asking here coz I need second and third opinions , the last time I took a colleague's word for it , I ended up spending $100 more than I should have

Have you checked the water pump? If the water pump impeller is failing, then the coolant won't be able to circulate as it should, especially when going uphill. ALso, the cooling fan can be the issue, check for a faulty fan, switch or relay.