Idle Noise

[inspection]

After lurking here for a while, I decided to go check out the TDI. While I am only intersted in a Passat wagon TDI with manual transmission, I looked at a Golf just to find out more about TDI.

This car had automatic, BTW, in Escondido, California for those who are looking for an auto transmission.

My overall impression was very good, except for the amount of engine noise at idle. At that point it seemed to be more like a diesel of old, and under all other circumstances, it would be difficult to determine the type of engine it had. Has anyone else felt that way? Comments?

 

[VWx6]

You are right. If you turn off the radio and the a/c so you can hear the engine, it does sound like a diesel. Compared to my last five diesels it is by far the quietest.

I like the idle sound of a diesel. In fact, I love it. That, of course, is a matter of taste.

Compared to older diesels, there is a complete absence of vibration at idle. Also absent is the loud clatter the old diesels made before they warmed up. That clatter was particularly loud on a cold winter morning, and the clatter, along with some pinging, really drew attention to the car for the first few minutes.

I doubt if someone unfamiliar with diesels would even notice a TDIs sound.

 

[diesel_freak]

I too think the sound of modern diesel at idle is a thing of beauty.

Stand in between two Ford pick ups at idle, one a PowerStroke diesel, the other any Ford gas engine. The PowerStroke sounds like it means business, the gas engine doesn't say anything.

 

[mickey]

Once you get rolling a TDI just sounds like a particularly powerful little gas engine. You only notice the "clatter" at idle. I love that sound too, within reason. The old Powerstrokes are too noisy for my tastes, but the new HEUI injector design is a lot quieter. (The '99 Powerstroke is basically a 7.3 liter Pumpe Duse! Yikes!) I absolutely hate the sound of the Cummins diesel in the Dodge trucks, especially the new 4-valve motors. You can't carry on a normal conversation in or around on of those things!

Mr. Inspection, if you want to make an honest comparison, drive the TDI and a gas-powered Passat on the freeway. A 4-cylinder gas motor will be a lot noisier. They have to turn more RPMs due to the relative lack of low end torque. I'm talking about the "old" Passats, mind you! The new ones are REALLY nice, but no TDI. Sigh. I'd give my left one for a brand new all-wheel-drive Passat TDI wagon with a 5-speed Tiptronic.

-mickey

 

[DT]

True, a diesel does sound different then a gas engine at idle. It has a deeper tone and a distinct clacking sound. The new VW TDI's also have a great interior cabin sound barrier system. It is much quieter inside, it always suprises me when I roll down the window at idle.

When driving (remember this what you are doing 99.9 % of the time) the TDIs deep rumble smooths out and is much more solid and satisfing then a whinney gas engine. At speed, shifting and cruising are at lower RPMs and is much quieter then a 4 cylinder gas engine.

Then there is the sound of the turbo. If you have your window rolled down and you give a little punch to the accelerator pedel you can hear the turbo spool up. It's a whirring whisper that turns into a zing, and then, back to a whisper as you release the accelerator. It is stunning.

No, a TDI is definatly not anything like a gas engine. Thank god and thank VW.


DT
1999 A4 Silver Jett GLS TDI

 

[SkyPup]

If you want to quiet the diesel idle noise down some, use full sytnetic oil and add cetane booster to your fuel supply, the cetane booster really quiets down the distinctive diesel engine idle noise alot. Using Premium diesel #2 with 45 cetane instead of truckers #2 regular with 40 cetane helps alot too.

 

[inspection]

OK, so now I know I wasn't imagining things about the noise at idle. I was very impressed with how the car performs and how quiet it is while moving.

Why is there such a difference between engine states and the amount of noise produced?

 

[VWx6]

Inspection, your question about the noise difference between engine states.

Okay. Blow up two balloons. One at ten times the atmospheric pressure and one at twenty times. Pop them. Which one is going to make the loudest pop? So much for the compression part of the noise.

Second, take two VWs, one a 2.0 gas, the other a TDI. Let out the clutch without giving either any gas. See how much faster the diesel will go. Try the same experiment going up an incline. The point is, that even at idle, the diesel is producing a lot of power, much more than as gas engine at idle.
More power, not just at idle, but all the way up the RPM scale. A TDI cruising will have a lower RPM that a gas at the same speed.

 

[diesel_freak]

Aside from the higher compression in a diesel compared to a gas engine, the other component of noise is the violent nature of the diesel fuel ignition compared to gasoline. A spark ignition engine will create a flame front at the spark plug which travels rapidly throught the cylinder. It is a combustion, not an explosion. A diesel, OTOH, injects an extrmely fine (and extremely volatile) mist into superheated air. This creates a much more violent combustion episode with the consequent extremely rapid pressure rise inside the cylinder. Why don't you hear the clatter above idle? Two things: first, combustions happen a lot more frequently, and your ear quickly loses the ability to distinguish between individual combustion events, also, the added road, wind, valvetrain, exhaust, and turbocharger noises combine to form a different sound signature.

A sound signature that is music to my ears. :^)

 

[N Dennis]

The only thing that sounds better than the whine of a turbo at full speed, is the sound of a Pratt-Whitney PT-6 on start up.

 

[mickey]

I would argue that the sound of female extacy has to rank fairly high on the scale of "sounds you want to hear". Unfortunately (for my wife) I have no direct experience with that sound...

-mickey

 

[SPUTNIK]

Where can I get a PT-6 and will it fit in the trunk of my A3 Jetta?

------------------

take a deep breath, this won't hurt at all

 

[diesel_freak]

Aye!! I forgot about the fabled Pratt & Whitney turboprop. I work on the Beech King Air assembly line, and I frequently make my way to the flight test area, where the sound of PT-6 engines firing up always makes me stop and savor the moment.

I LOVE THE SMELL OF JET FUEL IN THE MORNING! IT SMELLS LIKE VICTORY!

 

[N Dennis]

The smell of jet fuel...........Tim Allen says it best: "More Power!!!!!!"