Temperature of Car

[AzNMpower32]

Originally Posted by JCL

And if we consider most of the BMW coolant temperature gauges over the past decades, they haven't really been temperature gauges anyway. There were complaints that the needle wasn't in the middle where it should be, and it wasn't due to an engine problem, so a damping circuit was designed that essentially put the gauge at dead centre (12 oclock) for a wide range of actual engine temperatures. If the actual temperature was past a certain threshold, the gauge went to full hot. It didn't accurately indicate a range of temperatures, it was essentially an analogue idiot light. It had very limited value IMO.

Given the wide range of temperatures that the BMW engines run as "normal", it's probably appropriate too. I know the N52 runs anywhere from 80°-110°C based on driving load. The greater the load, the lower the temp.

[ard]

IIRC, in europe it has a temp gauge. Here in the US we get an astonishingly useless 'mpg gauge'.

And BGM, the sole reason they tell you to drive to warm it up is to reduce emissions...nothing to do with 'whats best for the car', but rather an overall 'global environmental impact' thing. Like not changing oil often reduces the impact of used oil on the environment.

[JCL]

Originally Posted by ard

And BGM, the sole reason they tell you to drive to warm it up is to reduce emissions...nothing to do with 'whats best for the car', but rather an overall 'global environmental impact' thing.

That isn't really true. Driving it right away is definitely better for the engine, as it reduces the warm-up cycle time. Faster warm ups mean less wear. If that helps the environment somewhat by reducing wasted idle time, great. It saves money too. Neither makes it wrong.

[deutsch100]

Originally Posted by JCL

That isn't really true. Driving it right away is definitely better for the engine, as it reduces the warm-up cycle time. Faster warm ups mean less wear. If that helps the environment somewhat by reducing wasted idle time, great. It saves money too. Neither makes it wrong.

One of my best friends is a Master Mechanic at an authorized BMW dealer, about 30 mins from where I live. He always tells me to just start the car and drive gently for the first 5+ mins or so. Starting the car and letting it "warm up" while idiling is REALLY bad for the car!!

[Penguin]

Originally Posted by deutsch100

Starting the car and letting it "warm up" while idiling is REALLY bad for the car!!

Back in the days of carburetors that was true, as the fuel mixture was very rich and the excess fuel washed the cylinder walls. With today's precision fuel injection, it is not that bad for the engine.

I do agree that there is no need for a lengthy idle warm-up, but it does depend on the temperature, e.g., if it was 20 below, I would not drive-off immediately.

If it's below 20 F, I typically give it 30-60 seconds before driving off gently.

[ard]

Just because a 'BMW Master Mechanic' says it does not make it true....

Until someone has actual wear data, I'm going to say that the 'wear reduction due to the decrease in warm up time' versus the 'increase in wear due to revving the motor to 2k, 3k rpm when cold', cannot be answered...and can be spun however you want to support what is in the owners manual.

Anyone have any DATA?

[JCL]

Originally Posted by ard

Until someone has actual wear data, I'm going to say that the 'wear reduction due to the decrease in warm up time' versus the 'increase in wear due to revving the motor to 2k, 3k rpm when cold', cannot be answered...and can be spun however you want to support what is in the owners manual.

Anyone have any DATA?

Yes, and the data has in fact been around for several decades. The myth that there is a benefit of trying to warm up engines with no load, at idle, just won't die.

Let start with this one from 2006:

Effect of Lubricant Properties and Lubricant Degradation on Piston Ring and Cylinder Bore Wear in a Spark-Ignition Engine

It goes into wear rates for piston rings and cylinder bores, considering them to be representative of other engine components (which I suppose we could debate). The over riding issue for wear rates, more important than viscosity, oil selection, oil additive levels present, engine aging, etc, was operation at cold temperatures. This article supports previous SAE studies that showed that cold engine wear rates were in the order of 20-25 times higher than warm engines. While not specifically addressing the tradeoffs of driving right away or not, it can been seen that the most critical factor is to reduce the duration of the warm-up cycle. Idling an engine just extends that cycle.

Spark Ignition Engine Performance During Warm-Up

This 1989 paper (Spark Ignition Engine Performance during Warm-Up) goes into the need for fast warm-up. You can discount all the fuel consumption and emissions reasons if you like, and just focus on the wear issues.

Engines Like to Be Warm

This 1964 paper titles Engines Like to be Warm supports the position that warm up time should be reduced.

Electronic System Reduces Warming-Up Period and Prevents Temperature Falling Down of Vehicular Engines in Long Low Power Situations

This 2000 paper concludes that engine warm up time should be reduced to minimize engine wear.

There is a very good paper that compares cumulative wear for two operating models, the extended warm up vs the 'drive it right away' model. I haven't found it yet, I've lost the link, but when I find it I will post it.

All of the 'drive it right away' suggestions are based on not using high rpm (for a BMW gasoline engine, I would use 3000 rpm as a limit, maybe less for a diesel). They assume that you do have oil pressure, which can take up to 10 seconds depending on ambient temperature. They also discuss not lugging the engine (moderate throttle), but making sure the engine has some load because that is what actually warms it up, not just spinning. Obviously idling an engine has no benefit for other stationary components (wheel bearings, differentials, etc) so I think we can consider wear in those systems to be a wash for either model of warm-up. Also, in very cold climates driver safety plays a role, in that you need to be able to see through the windshield. That would over ride the engine wear considerations IMO.

I am surprised that there are still doubts and questions about a practice that has been supported by the evidence for decades now. The advent of modern multi-grade motor oils is what made driving a vehicle immediately a better choice than idling it. Yes, there are side benefits to the environment (less pollution, less wasted fuel) but you can make a solid choice to not idle for warm up just based on reduced engine wear, if those considerations are not a factor.