Weird overheating S54

[Lukem3]

Hey guys desperately asking for some help, I'm a little stumped.

Quick backstory. Head resurfaced and gasket replaced because of bent valves and corrosion on surface of head when removed.
Every single coolant gasket replaced. Brand new waterpump, thermostat, upper and lower radiator hoses, fan clutch, both coolant sensors, overfill tank and hose. Also put a turner power pulley on at this time, without alternator.

Bled system 3 times already. Right after repair, would not hold pressure. Found a faulty waterpump gasket, the one from fcp came with a paper one. Replaced with a metal one from bmw and now holding pressure.

After about 20-30minutes of driving car will overheat when stopped at idle. Gets to the right white mark and i throw the heater one, not sure if it goes hotter don't want to test it out.
If i turn the ac on it will happen even if the motor is colder, only 5 minutes of driving or so. Only happens stopped at idle aswell.

Weird thing is when i start overheating, ill throw the heat on and let it get to center then drive with heat on until i get to my destination. If i shut heater off it won't overheat until the next stop, and it doesn't always do it either. If i shut the car off, when i start it back up sometimes it'll start getting hot right away on startup.

I took the power pulleys off, and it's pretty much the same. Takes a little longer to overheat but it still does it. Before the headgasket repairs it would rarely go above half. But it was also a lot colder, im currently in climates of 90-100°F. Last time driven before repairs was around 60°.
Thinking my aux fan at this point, but everytime i look at it, it turns on when it should. But everytime i look at it it's not overheating. Anyway to test this fan? If it is bad what are my options. Can't find much besides genuine bmw for like $600. Little pricey for an aux fan imo. Any other options or faults i could be looking at. I'm just stumped, doubt it's the headgasket since everything else is perfect. No faults in dme, no mixing of fluids or leaks. Full compression aswell, coolant system isn't over pressurized either. Any help highly appreciated thanks



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[sapote]

When you think the engine is hot, grab the radiator lower hose with you hand to see how hot it is -- can you hold it for 40 sec? Warm but not hot lower hose means not enough coolant flow through the radiator.

Electric fan should run during self-test when engine started up. Check mechanical fan with rolled-up paper.

[Mr.wReckless]

How prone are these engines and chassis' to heat soak? Especially if the radiator is getting old and inefficient on hot days with low airflow?

I've relatively recently refreshed most of the cooling system bar the radiator (2 years ago), and in todays heat (a measly 84F) on a spirited drive up a mountainside, I stopped and let it idle and the radiator and (mishimoto electric) fan couldn't cool the engine down, both water and oil slowly crept up from the middle mark. Same thing happened at a fuel stop. Car was stopped (i.e no engine driven pumps circulating fluids) and at the traffic light both temps started to creep up until I gained some speed. Only after hitting 30 mph it still took 15 seconds or so before the needles were showing a cooling down of fluids.

Water pump I know is new-ish, but not OEM BMW, oil pump I fitted a VAC motorsports upgraded flow version. So I'm wondering whether old and clogged radiators will have a play in this.

Regards

[sapote]

So I'm wondering whether old and clogged radiators will have a play in this.

It sounds like not enough air flow through the radiator. Either the fan not spinning fast or AC condenser/radiator are blocked with debris and dust over the years. I would remove the radiator and shoot the condenser with garden hose water forward and do the same on radiator.