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Discussion Starter #1
I have two questions I’m trying to ask to see what the other cars are doing:
1. With the car in drive and in comfort mode, holding the brake, the idle sits around 650 rpm or so. Is it normal if shifting the mode to sport (again while the car in drive and holding the brake), for the idle to go up to around 750, and then in sport plus for the idle to go to around 1000 rpm?
2. The fan seems to be almost all the time on is slow speed. Even with the outside temperatures in the 30s and 40s. I don’t mean when cold starting but returning from a drive. I let it idle for a number of minutes, fan doesn’t come off that low speed. Normal?
 

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The idle increases in the sportier modes to allow faster acceleration with less lag.

The fan is coolant temperature controlled as far as I know but there could be other factors like oil temp or air conditioning on or off.
 

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My expectation, with weather in the 30F, is that even after a relatively spirited driving, I come home, park, fan is in high speed, then after a while drops down to low speed (AC is not on, nor is defogger), then the fan should stop. It continues at low speed. I may try to really let it idle a long time, to see if it ever turns completely off.
 

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My expectation, with weather in the 30F, is that even after a relatively spirited driving, I come home, park, fan is in high speed, then after a while drops down to low speed (AC is not on, nor is defogger), then the fan should stop. It continues at low speed. I may try to really let it idle a long time, to see if it ever turns completely off.
Normal operation IMO. Mercedes/AMG really did a good job with the cooling system. The car will run the fan til safe temps even if you shut it completely off and it’s still warm, so unless you’re doing something like a track day or autocross and have to worry about heat soaking it you don’t have to really overthink it much. Maybe give it a couple extra mins if you come in hot from street racin some commuter cars in S+ lol, but overall it’s a very robust system.
 

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2. The fan seems to be almost all the time on is slow speed. Even with the outside temperatures in the 30s and 40s. I don’t mean when cold starting but returning from a drive. I let it idle for a number of minutes, fan doesn’t come off that low speed. Normal?
With the engine running it will still be creating heat that needs to be cooled off. This would require the fan to run to cool the coolant. If not the engine could overheat even at an idle speed. In fact, if the coolant is very hot the fan would run after turning off the engine.
 
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Discussion Starter #8
This is about how long the fan stays on in idle, not if it should come on.

When an engine is designed, a thermal balance is calculated.
On one hand, for the engine to have an increased efficiency, it has to warm up quickly, to where the cooling has to be minimal at the warming up stage.
Once the operating temperature is achieved, the thermostat opens and the radiator starts to be put to use.
The temperature can increase further, especially during the summer, or if you have the A/C on.
This is when the fan comes on, with two or maybe more speeds.
The radiator needs to have enough capacity to where during normal operation, the fan doesn't have to be on all the time.

If the fan has to be on all the time, for instance on idle, then there is an amperage demand on the alternator, which causes an increased idle fuel consumption.
Also the fan, like the starter as an electric motor, is designed with a certain duty cycle in mind. That duty cycle is not 100% on.

Now, for a car with Eco Stop engine function, the coolant has to be circulated with the engine off.
When stopped to a traffic light, is where the engine is hot from all that AC usage, and there is no more air flow across the radiator and the coolant pump stops, with the engine. This is where the coolant circulator pump steps in.

Once you have a coolant circulator pump on board, it makes sense to also activate it in order to prevent oil caking in the turbo bearings, which used to be done with a turbo timer, back in the day. The oil is removed from the turbo cartridge by gravity draining and being so hot, it drains easily.
SO as coolant flows through the cartridge water jacket, pumped by the electrical coolant circulator, the oil drips off and the caking doesn't happen.
Caking freezes an oil ring that sits on the turbine shaft and then oil seeps past the ring and into, impeller blades and into the ... exhaust, a potential emissions problem.
 

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I had similar questions when I got mine from out of state last summer. I brought it to a local, well respected Mercedes dealer for a courtesy check and they weren't surpised at all by the question about fan timings, ettc. There is more than one fan and circulation pumps that run at idle and after the vehicle is turned off. They have a fleet of 250s they use as loaners and have had a few 45s and said these things are all just rock solid, last forever, and have a lot of intelligence built in to make the engines last. Said it wasn't uncommon to hear fans and/or pumps cycle for a half hour after driving, nothing to worry about.
 

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Discussion Starter #10
Ok, thanks.
Another question:

do you guys have a flap inside the fuel tank filler neck?
In other words, once you open the fuel door and remove the fuel cap, there is the opening for the fuel pump nozzle, but most cars have inside that neck a steel spring loaded door. When you fill the tank, you have to push the fuel nozzle into the filler neck and open that door inside the filler neck of the tank.
may car doesn’t seem to have this.
 

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Ok, thanks.
Another question:

do you guys have a flap inside the fuel tank filler neck?
In other words, once you open the fuel door and remove the fuel cap, there is the opening for the fuel pump nozzle, but most cars have inside that neck a steel spring loaded door. When you fill the tank, you have to push the fuel nozzle into the filler neck and open that door inside the filler neck of the tank.
may car doesn’t seem to have this.
I do not have a flap inside the fuel filler neck.
 
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Discussion Starter #12
More questions:
Feeling vibrations in idle through the steering wheel is normal? (I may be used to the C63 with the V8 and Hydraulic steering, but seems like there's a low level vibration in the car)
Is there a way to tilt up the sunroof and yet still have the sunroof fabric underneath? I like to park the car with the sunroof tilted up in hot days, but not if the fabric can't be under it.
 

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I believe the fabric must come back, mine is earlier model and it always rolls back before I can tilt up.

No one mentioned this but part of that elaborate cooling also involves a very funny sound I occasionally get when I shut off when hot.....the sound of a flushing toilet I would best describe it as. It's got to be the moving of coolant, but it makes me smile. But on the electric fan, at times mine is on after I shut it off, and what a super quiet fan it is,you'd not know it turned on unless knowing what to listen for.
 

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The turbo revs up to 100,000 RPM. Getting a constant supply of oil to it's bearings is critical.

We used to install turbo timers that would allow the motor to run at idle for a while after you shut the ignition off. Why? To keep the oil pump operating to keep oil going to the turbo while it spooled down.

Not only are you worried about lubricating the bearings, but if the oil simply stops in the turbo it will coke and create big problems as well.

So part of what you are hearing is oil being pumped to the turbo.

Shall we discuss hot spots in motors and the need to circulate coolant to avoid head warpage while we are at it?

Ever walk by a Tesla in the morning when it is autonomously pre-heating the batteries before the driver is ready to leave?

Yeah, lots of stuff going on even if you aren't driving.

Modern cars ...
 
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