[tranquility]

I tried to google but it keeps misunderstanding me, giving me results about radiator fans, when to switch off the A/C, etc.

Anyway, my simple question is during a hot day, if I use the fan (not A/C), even w the lowest cold setting, the air blowing in is still warmish, so I want to just turn off the fan to avoid that, but in the back of my mind I somehow think that increases the chance of overheating the engine because there's no airflow and the hot air will get stuck in the engine bay??...but that couldn't be the case, right? Engine cooling shouldn't depend on passenger hvac settings?? I'm unsure so I rarely leave the fan completely off, just in case, but please tell me what is the right answer.

[POBEP]

Originally Posted by tranquility

I tried to google but it keeps misunderstanding me, giving me results about radiator fans, when to switch off the A/C, etc.

Anyway, my simple question is during a hot day, if I use the fan (not A/C), even w the lowest cold setting, the air blowing in is still warmish, so I want to just turn off the fan to avoid that, but in the back of my mind I somehow think that increases the chance of overheating the engine because there's no airflow and the hot air will get stuck in the engine bay??...but that couldn't be the case, right? Engine cooling shouldn't depend on passenger hvac settings?? I'm unsure so I rarely leave the fan completely off, just in case, but please tell me what is the right answer.

You overthinking it. It will be fine.
I drive with fan off on occasion (1:5) and never had cooling issue in 13 years.
The electric coolant pump will handle it.

[heavyD^2]

OP's concern was more prevalent in the days of pulley driven mechanical fans when stuck in low speed traffic at high ambient temperatures. It's not really an issue with modern vehicles with electric fan cooling and better engine cooling technologies.

[tranquility]

Originally Posted by heavyD^2

OP's concern was more prevalent in the days of pulley driven mechanical fans when stuck in low speed traffic at high ambient temperatures. It's not really an issue with modern vehicles with electric fan cooling and better engine cooling technologies.

I get what you wrote but my concern about hvac has no bearing regardless of fan system, right?

[Efthreeoh]

The HVAC system has zero to do with engine cooling capacity when both systems are in good* operational states. The blower fan in the HVAC will not affect the cooling ability of the engine cooling system. When not using the AC, the coolest air available is the ambient temperature of the outside air the car is travelling through. It will be a few degrees warmer though, because the HVAC plumbing (vent system) is under the dashboard and windshield and picks up radiant heat and stores it in the plastic, which transfers to the air flowing through the HVAC system. It is perfectly fine to drive the car with the HVAC system turned off. The hot air of the engine bay does not travel through the cabin HVAC system. Hot engine bay air flows out the bottom of the car. The HVAC system draws outside air for the cabin from in front of the windshield. There is a seal between the engine bay and the HVAC intake. On the E9X it is the rubber seal on the lower cabin airfilter tray that seals when the hood is closed.

* in the case where the engine is overheating or running very hot, using the heater can slightly reduce the coolant temperature as the heating core acts as a secondary heat exchanger (i.e. radiator) to bleed off a small amount of heat from the coolant. The passenger compartment gets a bit warm though in the summer.