One common concern about buying a diesel engine is that it sounds like a truck. Well, let's take a look at the decibel readings for our long-term 2009 Volkswagen Jetta TDI versus a variety of other engines and cars. These were taken at our two test track locations with differing surface and wind conditions (nothing overly gusty), so these numbers aren't exactly precise down to the tenth of a decibel, but general comparisons can be made.
2009 VW Jetta TDI
Idle: 47.7
Full Throttle: 72.8
70-mph cruise: 70.0
2005 VW Jetta TDI
Idle: 48.7
Full Throttle: 75.8
70-mph cruise: 68.8
2008 VW Jetta SE with 2.5-liter five-cylinder
Idle: 42.5
Full Throttle: 73.8
70-mph cruise: 68.7
2009 VW CC 2.0T
Idle: 48.5
Full Throttle: 73.0
70-mph cruise: 67.0
2008 Ford F-450 Super Duty with turbodiesel
Idle: 51.4
Full Throttle: 68.4
70-mph cruise: 67.9
2009 BMW 335d
Idle: 46.0
Full Throttle: 72.6
70-mph cruise: 64.0
2009 Toyota Prius (no 2010 data available yet)
Idle: 39.2 (engine off) 42.6 (engine on)
Full Throttle: 70
70-mph cruise: 68.0
2010 Honda Insight
Idle: 44.2
Full Throttle: 72.5
70-mph cruise: 68.8
2009 Honda Fit Sport
Idle: 40.8
Full Throttle: 75.8
70-mph cruise: 67.6
2009 Mazda 6i with 2.5-liter four-cylinder (noted for being rather loud)
Idle: 44.9
Full Throttle: 71.3
70-mph cruise: 67.0
James Riswick, Automotive Editor @ 16,400 miles
cocarguydj says:
09:27 AM, 05/14/09
That is hilarious that the F-450 is the quietest of all of these vehicles at full throttle, and only noticeably louder than the others at idle really. Ford must have done a good job with the sound deadening materials in the cab.
I also find these sorts of generalizations to be interesting(i.e. all four-bangers sound like...).
felonious says:
09:32 AM, 05/14/09
Cocarguydj beat me to it.
wobbly_ears says:
10:00 AM, 05/14/09
For me, it isn't the decibel that is irritating, rather it's the 'rat-a-tat' sound diesels make. The diesels still sound as if there's a loose chain in moving around in the engine bay. The gas engines sound more 'tight'.
yellowbal says:
10:08 AM, 05/14/09
Remember that a 3db change is about double the "loudness".
That means my Civic Si is about 4-6 times louder than the BMW 335d @ 70mph.
dougtheeng says:
10:18 AM, 05/14/09
You can't even tell you're driving a diesel vehicle when I drive my 2004 VW Golf TDI on the highway. The only time its really noticeable is during cold morning starts and when you have the windows down.
ahightower says:
10:26 AM, 05/14/09
Wait, the Prius makes 39.2 with the engine off? Did you forget to turn off the radio?
jasbra says:
11:40 AM, 05/14/09
@ahightower - A mosquito's buzz is rated at approximately 40db, so that's actually quite quiet. I'm sure there was some ambient noise going on outside the car, so some noise from the electronics.
rick8365 says:
12:04 PM, 05/14/09
@wobbly - I love the ultra refined sound of something like BMW's I6 but I also love the mechanical sounds of a diesel. I had a gas Ranger with a wrist pin problem - sounded a little like a cross between a diesel and a coffee can of marbles at idle....could not stand it (Ford replaced the engine). But if it had been a diesel under the hood, I'm sure I would not have been bothered by it - probably would've loved it.
audisport says:
12:29 PM, 05/14/09
My 2.0T Audi sounds like a diesel at idle.
caheew says:
12:36 PM, 05/14/09
Wow, a lot of these cars are quieter than I thought. The Fit is pretty good on the highway and during idle, and that 335d is supremely quiet.
sherief says:
01:00 PM, 05/14/09
I like the diesel clatter.
Audi's 2.0T FSI motors clatter like diesels because they have high compression and very high pressure fuel injectors.
brn says:
01:25 PM, 05/14/09
I can't wait to see my friends that own Priuses and tell them how noisy their cars are compared to a F450. I don't think they'll believe me.
bimmerjay says:
01:43 PM, 05/14/09
"One common concern about buying a diesel engine is that it sounds like a truck."
So it's relatively quiet... big whoop. As your sentence insinuates, it's not about the LEVEL of sound, it's the QUALITY of sound. Post a somehow-objective sound quality measure of these vehicles and maybe then, but only then, would I be possibly half-interested.
That is all.
rickallen says:
05:15 PM, 05/16/09
Jeez, I knew my TDI was loud, but not THAT much louder than these. My old car was a 2007 Civic Hybrid. It was quiet around town, but roared pretty bad on the highways. Mostly, I bet it was my tires.
My Jetta is loud almost everywhere, but it's not the engine. The engine is only noticeable at acceleration, but drowns out quickly to a slight hum. The wind and road noise are bad, but made worse by the stereo's inability to cover it with anything worth listening to. The speakers are of such low quality, they make my ears hurt when played at "jam volume" or at sufficient volume to hear it on the freeway.
gearcat says:
01:55 AM, 05/18/09
One of the things I always loved most about diesels is the clacking ... or in the case of the larger displacement diesels, the purring. Unfortunately (for me) most of the smaller displacement diesels are getting more and more quiet. Even if it is a noisy diesel, once you're up to cruising speed, you can't tell it's a diesel under the hood.