There is a plastic flap that run along the bottom of the radiator on the front of the car. This is supposed to direct air upwards when driving.
In regards to the fan, is this a 2 speed fan?
What type of gauge are you using? Hopefully not stock.....
1. Add coolant and be sure that your coolant is good. You've done this. That's only STEP 1 in diagnosing.
2. Check your oil level and see if there's coolant present. Coolant in the oil typically looks like a whitish paste. If this is the case, there is a leak internally somewhere. Most likely, your head gasket.
3. You need to do a pressure test on the system while its cool. to be sure you don't have an externally visible coolant leak somewhere. If you find a leak, you need to fix it (obviously). You should also be checking to be certain the cap on the radiator is sealing properly. There will typically be yellow gunk around it if its been leaking. Same with the oil cap. You can rent the tester for free from your local auto parts.
4. Check to see if your thermostat is functioning. Some people can do this on the vehicle by squeezing the coolant hose, and waiting until the thermostat opens. When this happens, you can feel the pressure in the hose change. My personal recommendation is to put it into a pot of water and set it to boil. If its functioning, it will pop open right around boiling temperature. If it doesn't open... it isn't functioning.
5. Inspect the belts and the water pump. Does your water pump have any shaft play? Is the belt installed properly, or failing somehow? You can also manually turn the water pump to be sure its actually movable.
6. Is there any type of blockage to the cooling system? Is your radiator fan spinning, and turning on and off as necessary? Is your A/C installed and does it work? Is it on when you're doing this?
If you're ONLY noticing overheating at high engine loads, I would suspect it isn't a fan related issue since it is new.
2016 VW GTI 2.0 Turbo
1989 Sonic Blue LX Coupe, 349 ci, TW heads, TFS Track Heat Intake, 75mm Accufab TB, 80mm ProM, 30 lb. inj, TKO, 3.73, 31 spline w/ TruTrac, MAC 1-5/8" LT headers w/ H pipe, Flowmaster, electric fan Moates QH
391 rwhp & 424 rwtq...Mustang Dyno 11.5@122mph