[No one]

Originally Posted by baron95

I can't believe people are still repeating the old wives' tale about idling the car to let the turbos cool before shutdown. Are they deaf? Don't they hear the fan and pump going after shutdown on modern cars? My M2 does it plenty loud. My Jeep does it plenty loud.

No, I don't. I park meticulously and it always has the time to cool naturally.

[KevinGS]

Originally Posted by Redd

Here's proof that you should warm up your car.

Top pic are my rod bearings at 90k kms shortly after I purchased it. The car was in generally rough shape and it was obvious the PO had not taken care of it.

Bottom pic are my rod bearings when they were replaced earlier this May 2026 after 80k kms / 10.years of use. The main difference - I always warmed up 1 min from cold start, at least 15-20 seconds from warm start, and I maintained below 3k rpms until oil temps reached 85C.

So yes, warm up your cars.

I have a 2013 M3 with the S65, an engine with known rod bearing issues. And I rarely warm up my car.

And I drive my M3 year round, from 105 degree summer days to 0 degree winter nights. Occasionally in the winter, I warm it up for a few minutes if I need the windows defrosted. Otherwise, I just get in and drive off, even when it's 5 degrees outside. The warm up time is as long as it takes for me to buckle my belt, and queue the song I want to listen to.

My car has 160,000 miles, with its original rod bearings, running just fine.

Having said that, I keep the RPMs pretty low until the oil temperature rises to a suitable point, which could take a while on a cold winter day. Other than that, I just get in and drive off, every time.

So, maybe, your rod bearings looked like that for a different reason.

Plus, I'm fortunate to also have a twin turbo G82 M4, and if I'm ready to turn the engine off right after a super aggressive drive with lots of near-redline shifts, I will occasionally let the car engine run for a few minutes, out of sheer habit. But when I don't, and I just the turn car off right after an aggressive run, the car fans stay on for a while doing their thing. Modern turbos have all those computerized fans for a reason.

Oh, and my M4 has 120,000 miles. Yeah, I drive my cars.

[BruinMan]

What BMW generally recommends:

* Start the engine
* Wait about 10–30 seconds for oil circulation
* Drive gently until the engine warms up

The fastest and healthiest way to warm the engine, transmission, and differential is actually light driving — not extended idling.

Really cold freezing morning - 30 seconds to about 1 minute.

After hard driving or highway pulls, give the engine about 30–60 seconds of easy driving or light idle before shutting it off. That helps reduce heat stress on the turbochargers.

[baron95]

Originally Posted by MJBO

Everything in both photos looks shagged.

Shhhh...don't ruin his "proof".

[baron95]

Originally Posted by BruinMan

What BMW generally recommends:

* Start the engine
* Wait about 10–30 seconds for oil circulation
* Drive gently until the engine warms up

The fastest and healthiest way to warm the engine, transmission, and differential is actually light driving — not extended idling.

Really cold freezing morning - 30 seconds to about 1 minute.

After hard driving or highway pulls, give the engine about 30–60 seconds of easy driving or light idle before shutting it off. That helps reduce heat stress on the turbochargers.

There is a section on BMW manuals for "Highway Pulls"?

A) Highway Pulls, whatever that means is not hard driving.
B) Unless your garage is on the highway, getting off the highway after the so-called highway pulls would be plenty of cool down time.

Do people have any concept of what hard driving actually is? On a typical 30 min track session, I'm at WOT ~40%-50% of the time, and at or above ~5,000 RPM nearly 100% of the time, and the M2 is like "are we just warming up or what?"

[T.R.S.]

Originally Posted by Redd

Here's proof that you should warm up your car.

Top pic are my rod bearings at 90k kms shortly after I purchased it. The car was in generally rough shape and it was obvious the PO had not taken care of it.

Bottom pic are my rod bearings when they were replaced earlier this May 2026 after 80k kms / 10.years of use. The main difference - I always warmed up 1 min from cold start, at least 15-20 seconds from warm start, and I maintained below 3k rpms until oil temps reached 85C.

So yes, warm up your cars.

That's not "proof" of anything.

[pbonsalb]

Originally Posted by Redd

Here's proof that you should warm up your car.

Top pic are my rod bearings at 90k kms shortly after I purchased it. The car was in generally rough shape and it was obvious the PO had not taken care of it.

Bottom pic are my rod bearings when they were replaced earlier this May 2026 after 80k kms / 10.years of use. The main difference - I always warmed up 1 min from cold start, at least 15-20 seconds from warm start, and I maintained below 3k rpms until oil temps reached 85C.

So yes, warm up your cars.

Anyone who knows anything about E9x M3 and the S65 knows that the rod bearing problem those engines have, like the S85, is not due to failing to sit idling for 10 minutes before driving off or turning off the engine. I had a 2008 E90 M3 for 10 years and know a lot, and I changed the rod bearings myself as preventative maintenance. Most of the engine builders attribute the wear to the very tight bearing clearances, which are far below industry standards.

However, some think the 10W60 oil may be too thick for the tight clearance when cold, so your long warm up would help if the oil thickness is the real problem. One engine builder recommended using 5W50. I used 5W40.

An engine builder also recommended running a hotter coolant thermostat. The stock one is around 70C or 160F and that is pretty cold for a modern engine. The oil runs hotter than the coolant. I changed to the engine builder’s recommended 90C thermostat, but that caused the engine cooling fan to run more. Probably coding or a change in the tune could have synchronized them.

From 2008 until 2010, the rod bearings were lead based. The EU banned lead so the bearing material changed. If you had the earlier bearings and looked at them at 60k miles and then changed to the later ones and looked at them at 80k, any visual comparison would not be fair. Also, many shops changing bearings after 2012 use extra clearance bearings to address the overtightened clearance problem. It would also be unfair to compare wear on those bearings to the early bearings when trying to make a case that failure to do long idling prior to driving is the cause of wear on the early bearings.

[RockCrusher]

Originally Posted by baron95

The most important thing is to make sure the engine has reached full normal temperature for several minutes at THE END of the trip. If I need to drive a mile to the gym or the store, I will remote start the car, and or drive longer/harder as needed to make sure oil has full temp for a while before shut down.

Most people worry about the beginning of the trip (when should I start driving, etc?). The focus should be at the end (has the car run enough at temp before shutdown?).



P.S. I can't believe people are still repeating the old wives' tale about idling the car to let the turbos cool before shutdown. Are they deaf? Don't they hear the fan and pump going after shutdown on modern cars? My M2 does it plenty loud. My Jeep does it plenty loud.

My M8 circulates coolant after engine shut down to cool the turbos. But I still will let the engine idle maybe a minute or two if the engine oil temperature/coolant temperature is elevated.

I do this to reduce the wear and tear on the battery which powers the auxiliary electric water pump and radiator fans after the engine is shut off.

[pbonsalb]

If you have just gone on a long drive and the battery is fully charged, will it continue charging during this file procedure or will the idle procedure just drain the battery a little? These cars essentially turn off the alternator whenever possible if voltage is sufficient to safely run the car without charging. After a long drive, the matter might be fully charged and the alternator decoupled. I do not know the answer.

[Efthreeoh]

Having owned BMWs since 1988 and driven well over 1M without an engine failure, I'll chime in about warm up.

You'll find in older BMW owners manuals that the proper cold engine driving protocol is to start the engine and drive at moderate speeds, which allows for the best warm up of the driveline components. The owners manuals define "moderate speed" as avoiding heavy throttle application and remaining under a specified RPM until the coolant temperature gauge needle moves out of the blue zone on the gauge face. For example, my E30 stated not to exceed 3,000 RPM until the coolant gauge was out of the blue zone. My Z3 upped the RPM to 4,000 (smaller 4-cylinder engine).

Yes, some more modern BMWs did not/do not have coolant temperature gauges, but the procedure is the same; cold start/drive away at moderate speeds. As we know the N52 E90 has no coolant temp gauge, so I just drive at moderate speeds until the heater is making warm air. Interestingly, the E90 M3 had a variable redline built into the tachometer to aid the driver in not exceeding maximum engine speeds for a given coolant temperature, which validates BMW's cold engine protocol.

The idea of warming an engine is to give time for the internal metal engine components to expand to their normal operating dimensions for the designed bearing clearances of the engine (just not crankshaft bearings). Metals are very good at conducting heat transfer. The internal components heat up rather quickly considering the high thermal load of thousands of repeated fuel/air explosions inside the cylinders. The warmup period is not to give the oil time to heat up for better lubrication performance. Oils provide lubrication over their weight range (i.e. 5W-30) and don't lubricate better at higher temperatures.

[RockCrusher]

Originally Posted by pbonsalb

If you have just gone on a long drive and the battery is fully charged, will it continue charging during this file procedure or will the idle procedure just drain the battery a little? These cars essentially turn off the alternator whenever possible if voltage is sufficient to safely run the car without charging. After a long drive, the matter might be fully charged and the alternator decoupled. I do not know the answer.

With the engine idling the battery will not supply the electric power to run the fans and the auxiliary electric water pump.

While the engine is running the alternator supplies all the electrical power the engine/vehicle needs. Chances are high the battery is topped up sufficiently and the alternator is not feeding the battery any power.

With the engine running the electric fans are powered by the alternator. The auxiliary electric water pump is not needed. With the engine running the water pump driven by the serpentine belt circulates coolant. And the engine driven oil pump circulates oil.

At idle other areas of the engine also have time to shed some heat load.

At engine idle the exhaust gases are relatively cool and this cools down the exhaust valves (which in turn reduces the amount of heat the exhaust valve seals are subjected to after the engine is shut off) and the cooler exhaust in turn also cools the turbos and at their hottest areas.

Idling also gives the automatic transmission time to shed some heat load.

If after engine shut down the auxiliary post engine shutdown cooling systems are deemed necessary I believe their operating time will be shorter than if I had not idled the engine.

Just to be clear it is not like I feel I have to let the engine idle any real length of time. I do not subject the car to hard driving on the way home from wherever I have been. It is about 3.5 miles from the nearest freeway to my house. This 3.5 miles consists of surface streets with a speed limit of 45mph. Any exceptional heat load that the engine may have from the freeway has been minimized by the time I reach home and have backed the car into the garage.

But I still allow the engine a minute or so of idle time.

[brianeck]

The car is ready to drive upon starting. If your temperatures are mega cold, like 0 Fahrenheit or below your liquids could be running a bit thick, I would always suggest a little warm up in those conditions. Otherwise the car is meant to be driven during warmup - just dont go WOT pedal to the floor until your temperature is above the cold line, once its past there then do as you please.

Its high pressure situations with "slow" liquids that are too cold that cause issues - regular friving is not an issue but pedal down is.

[pbonsalb]

Originally Posted by RockCrusher

While the engine is running the alternator supplies all the electrical power the engine/vehicle needs.

This is the way charging systems used to work back in the old days. But these days, the alternator is turned off much of the time and the battery is used. This is a fuel saving measure adopted by Porsche, BMW and others; another one is specifying thinner oils. Then the alternator is turned back on during deceleration to charge the battery.

What I do not know are all of the conditions when the alternator is drawing engine power. You are suggesting it is always on at idle, but I have not found specific documentation other than the general concept that if the battery is depleted to a certain level, the alternator will engage no matter the rpm or load.

[No one]

Originally Posted by pbonsalb

This is the way charging systems used to work back in the old days. But these days, the alternator is turned off much of the time and the battery is used. This is a fuel saving measure adopted by Porsche, BMW and others; another one is specifying thinner oils. Then the alternator is turned back on during deceleration to charge the battery.

I don't know about these days, but BMW promised the Efficient Dynamics feature of "brake energy regeneration" for my car (page 16 of the brochure) back then. And here is what it turned out to be: https://f20.1addicts.com/forums/show...5#post30143985. The alternator looks belt driven. How they would detach/attach it to the engine is most unclear.

[pbonsalb]

The charging circuit is disconnected so the alternator freewheels and there is virtually no drag when charging is not needed. I agree the braking regeneration thing is a bit misleading. Energy is not being harvested from the slowing of the car but rather the alternator is being allowed to charge the battery during braking and deceleration. There is nothing unclear to me except the exact terms of alternator engagement, and I am not sure it is always engaged at idle producing electrical power like an alternator would in the old days.

Long, long ago, I had a vacuum operated device called Alterbreak that would turn the alternator off when vacuum was close to zero, reducing parasitic drag by a few horsepower. It had an adjustable threshold and an adjustable minimum voltage at which the device would allow charging. Might have saved a tiny bit of gas as well.

[No one]

Originally Posted by pbonsalb

The charging circuit is disconnected so the alternator freewheels and there is virtually no drag when charging is not needed.

I was omitting the fact there was an electromagnet(ic rotor) that could be cut off inside the alternator. It's just not the battery but the rotor charging circuit is disconnected so the alternator freewheels.

[BruinMan]

I see some bad answers and some very good correct answers. This is what I found out for my X5.

2021 M50i relies on BMW’s traditional 12-volt Brake Energy Regeneration system.

How it actually works on your V8 M50i Intelligent Alternator Control:
Instead of a hybrid electric motor, the vehicle uses a specialized AGM 12-volt battery and an intelligent alternator management system.

Decoupling Under Load: When you press the gas pedal, the engine management system completely decouples the alternator from the engine. This ensures all 523 horsepower goes directly to the wheels without any parasitic drag from charging the battery.

Energy Capture: When you lift off the accelerator or step on the brakes, the alternator re-engages. It uses the SUV's coasting momentum to spin the alternator, capturing that free kinetic energy and routing it back into your 12-volt battery.

I hope this clears up some confusion.

[Tejas1836]

Originally Posted by BruinMan

specialized AGM 12-volt battery

Any 12v AGM will work [with appropriate specs]

[pbonsalb]

Originally Posted by BruinMan

I see some bad answers and some very good correct answers. This is what I found out for my X5.

2021 M50i relies on BMW’s traditional 12-volt Brake Energy Regeneration system.

How it actually works on your V8 M50i Intelligent Alternator Control:
Instead of a hybrid electric motor, the vehicle uses a specialized AGM 12-volt battery and an intelligent alternator management system.

Decoupling Under Load: When you press the gas pedal, the engine management system completely decouples the alternator from the engine. This ensures all 523 horsepower goes directly to the wheels without any parasitic drag from charging the battery.

Energy Capture: When you lift off the accelerator or step on the brakes, the alternator re-engages. It uses the SUV's coasting momentum to spin the alternator, capturing that free kinetic energy and routing it back into your 12-volt battery.

I hope this clears up some confusion.

The 2021 X5 M50i has 2 batteries. Maybe one of them is “specialized.” Perhaps that term defines its purpose as different from the starting battery? My 2018 M5 has only 1 battery and it is lithium ion. I think it still decouples the alternator much of the time and charges when coasting, braking or decelerating. I would call that more of a smart alternative control than regenerative braking. It is not like the braking creates energy that is turned into electricity. The charging while braking seems no more efficient than the charging while coasting or decelerating.

[No one]

Originally Posted by pbonsalb

It is not like the braking creates energy that is turned into electricity. The charging while braking seems no more efficient than the charging while coasting or decelerating.

Engine braking does. But you (mostly?) need a MT for that. I read with AT (which is bullshit by itself ) they (Porsche in particular, others too?) added coasting in neutral for longer range and fuel economy. Back then a car's manual would warn against driving in neutral as that affects car control (without electronic assistants) and brakes heating/wear too.

[pbonsalb]

Yes, my 2021 Cayenne S will coast.

But while braking can create energy that can be turned into electricity, BMW’s so called regenerative braking is not doing it, at least on the older non hybrid cars. Rather, alternator charging is allowed during braking just like it is allowed on deceleration or coasting.

[tracer bullet]

Originally Posted by pbonsalb

But while braking can create energy that can be turned into electricity, BMW’s so called regenerative braking is not doing it, at least on the older non hybrid cars. Rather, alternator charging is allowed during braking just like it is allowed on deceleration or coasting.

Not to have a semantics argument here, but you're saying braking doesn't generate electricity then explaining how it does indeed create electricity.

It's not a classic hybrid car or setup, we agree, but braking is, at times, being used specifically to create electricity.