Car Care: How long to warm up - Part II

[M A V I C]

original thread: http://forums.macresource.com/read/1/85419/86028

I usually let the engine warm up enough that the RPMs drop down. The past couple days I've let it warm up for 30 seconds or so and then drive. Well, when I do that the engine seems to rev higher than it usually does to accelerate at the same rate. In other words, it seems to have a lot less power.

It revs up to about 3500. Normally it goes to about 2200 and shifts. After a minute or so, it's back to normal. The tach goes to 6500 before it redlines.

I figured I should see what the manual says. To my surprise it says do NOT let the engine idle after starting it. That one should drive off immediately after starting the car. The reason for this is it takes a long time for the engine to warm up when idling, and that the engine wear when idling is greater than driving at low RPMs. So it says to drive off, but not rev the engine very high.

Strange.

[BigGuynRusty]

Not strange.
What is this mystery vehicle?
Also, engines are built to exacting standards, need little to any break-in, were talking Japanese cars, not GM, search piston slap, and Silverado for a list of angry truck owners!

BGnR

[bangman]

Why is this a surprise? I sent you a link with an explanation from CarTalk that detailed it well.

[AlphaDog]

Yup, when all else fails, read the directions.

[M A V I C]

It's an audi with a 2.7T.

The engine is also abnormally loud when it starts out, and I'm not just talking about engine revs. If I let it idle for a bit, the sound quickly goes away.

The strange part I was referring to was that, when I don't let the engine warm up at all, it is very underpowered and requires higher revs to get it going. Whereas, the instructions say to start immediately driving but keep the revs low.

[msglee]

They also want you to drive off right away to get better gas mileage. Your not getting any mileage sitting there.

[Filliam H. Muffman]

The reason that the engine noise goes away is that the catalytic converter is getting coated with soot from the over rich mixture. As it plugs up it creates more backpressure and the noise goes away. (kidding?)

Lets look at the syptoms of the turbo motor: louder, less power, more revs needed before it warms up. Maybe the boost is being limited until it warms up. Without as much boost the engine needs more revs to generate the same power. Less boost means the turbo is restricting the exhaust less and it is louder.

At least you are not having battery problems with this car.

[elmo3]

M A V I C Wrote:
-------------------------------------------------------
> The strange part I was referring to was that, when
> I don't let the engine warm up at all, it is very
> underpowered and requires higher revs to get it
> going. Whereas, the instructions say to start
> immediately driving but keep the revs low.
>
>


It does not *require* higher revs. The engine management computer is, however, forcing higher revs in order to warm up the catalytic converter more quickly--which leads to lower emissions.

There's nothing strange about this at all. It's all taken care of in the engineering. The higher revs called for by the engine management computer are not the type of high revs that the manual warns you against.

[M A V I C]

Thanks guys. I was guessing it was something like you mentioned, but wasn't sure. It's a used (though certified) car, just a few weeks old. I wasn't sure if that's the way it's supposed to work. It makes a funny sound when it starts cold as well (a ticking sound, goes away after 5 seconds or so.)

[BigGuynRusty]

Filliam H. Muffman Writes.:

"The reason that the engine noise goes away is that the catalytic converter is getting coated with soot from the over rich mixture. As it plugs up it creates more backpressure and the noise goes away. (kidding?)"

You have to be kidding!
Big hole in your "Plugged Converter Theory", the sound would come back as soon as the converter lights off.
Most likely a little bit of piston rattle that goes away when it warms up.

BGnR