# How's your car run before it's warmed up?



## nok (Mar 14, 2010)

I've noticed that my 335d has a bit of a stumble as soon as I hit the road in the morning. It smooths out after a couple miles, but I don't believe it's always done this. Do any of the rest of you notice this?


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## grapes87 (Feb 22, 2011)

I haven't noticed it, but then again I don't know when my car truly warms up due to lack of gauges. At any rate, my car is garaged at both home and work, thus most of the time it is started at a higher ambient temperature than if it were outside.


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## János (Jun 19, 2010)

Morning ambient temperatures are usually in the 50's where I live. I notice a bit of a "gritty" sound quality to the engine when I first drive off and the car can feel a bit sluggish. That disappears within a mile or so... and then it just purrs nicely. I like to think of it as extra 'character'!


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## Snipe656 (Oct 22, 2009)

I have not noticed it on mine but can say I have pretty much noticed that in any other diesel I have been in and would imagine it is just common place for such motors. I probably don't notice it in mine because I am so used to my truck that is horrible when it has not warmed up.


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## AZ335D (Aug 19, 2010)

Even when my truck is warmed up, I have to shut it off when I stop at the drive up window of a fast-food place. At least the d is not that loud (even when cold).


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## AutoUnion (Apr 11, 2005)

It's quite rough and jerky for the 1st couple minutes. My old VW TDI was the same way. After a little while, the engine is fine.


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## Snipe656 (Oct 22, 2009)

The only diesel I own that is quite rough and jerky when cold is my truck and it has to be well below freezing for that. I'd actually never even think to use rough or jerky for the two cars.


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## Philm35 (Aug 19, 2010)

Mine runs very smoothly from the get-go. I do notice that the transmission is slow to upshift before the car warms up... shift points are about 1000 RPM higher. I usually paddle it into the next higher gear manually for the first mile or so.


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## grapes87 (Feb 22, 2011)

Philm35 said:


> Mine runs very smoothly from the get-go. I do notice that the transmission is slow to upshift before the car warms up... shift points are about 1000 RPM higher. I usually paddle it into the next higher gear manually for the first mile or so.


That's true of mine as well, in the winter when its parked outside.


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## rmorin49 (Jan 7, 2007)

Other than a delayed 2nd to 3rd gear shift, I have noted no difference.


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## dunderhi (Dec 10, 2006)

I haven't noticed any difference between cold and warm starts, but my D is garage kept and I normally use the manual shifters.

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## Snipe656 (Oct 22, 2009)

Mine too is garage kept or car port when at work and I never have noticed this shifting issue when first getting into the car but enough people mention it so must be more common than not. What I have noticed many times is my car will not fully engage into reverse if the car has been sitting for a long period of time. Not sure how long it has to sit or if the time period is even the key to it. Just noticed though many times when it has been parked for a week or more then I get into it and put it into reverse that the car does not move. I have to give it a bit of throttle before it will move. It has been looked at once for this but nothing was found, but since I have no way of definitely making it repeat then that probably helps none in diagnosing it.


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## autoJeff (Oct 1, 2009)

I live in a hilly neighborhood and have a steep driveway. I do not notice "hard shifts" when the car is cold. I do, however, wait to feel the transmission engage forward gear before I start driving up the hill, after backing downhill out of my driveway. 


The car definitely holds higher RPM when things are cold, while accelerating or while climbing a hill, until a few seconds after it has reached 45-50 mph steady state speed. I think that behavior is supposed to somehow help reduce emissions. But I don't understand the logic.

Assuming a given desired acceleration curve, I'm guessing that higher RPM means increased exhaust gasses, which means increases air mass in the cylinders. Does a larger air mass result in reduced emissions? Or maybe more frequent, but less potent, combustion causes crank case temp to raise more quickly?

I think I read in the workbook document that the SCR system does not begin injecting DEF until temp has risen past a threshold. That ensures moisture has been removed from the NOx sensor. So it makes sense that raising temp quickly helps reduce emissions. That's more reason to drive away shortly after starting the engine. Also, the diesel doesn't generate enough heat at idle to effectively bring the engine to normal operating temperature.


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## grapes87 (Feb 22, 2011)

Jeff: I think the point is not to reduce initial pollutants but rather to get the engine at a higher temperature faster and overall having it operate more efficiently over the course of the trip, reducing overall pollution. :dunno:


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## Snipe656 (Oct 22, 2009)

Could it also be a method for warming up the transmission?


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## taibanl (Oct 3, 2010)

Seems mine hesitates a bit the first few blocks. Dont think it used to do it


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