How to Drive a TDI

McComb.com

Active member
Joined
Feb 5, 2001
Location
Portadown, United Kingdom
TDI
Jetta UK SE 2.0 (140)
Hi all
Can you settle an argument?

My work colleague and I differ about how to drive our TDI’s.

1. I drive through the gears by changing up when the revs are between 2500 and 3500. I also do this in first gear.

2. He changes gear as soon as the revs reach 1500 and changes out of first as soon as possible.

Who is driving the best for fuel economy and/or least wear and tear on our engine and gearbox?

Regards

Trevor McComb
trevor.work@mc-comb.com
 

mbciii

Veteran Member
Joined
Feb 13, 2000
Location
Somewhere Over the Rainbow
Mr. McComb,

I think your friend has the high ground here. But only slightly. Your driving habits are closer to my own. But I drive, shall we say, enthusiatically?

Given that he is being "feather-footed", those 1500 rpm shifts of his should yield him much better fuel economy. It should also earn him impatient glances and rude gestures from little-old-ladies!


From a wear-and-tear perspective, well, theory says that the less work the engine does the longer it will last. These are stout little motors however, and I suspect that they are more than up to the task.

There is one other consideration. Does your friend, (and come to think of it, do you) occasionally let the engine run all the way up?

The occasional third gear full throttle blast out on the interstate (what do you guys call them over there?) serves a couple of purposes:

1. Blows soot from exhaust system.
2. Allows catalytic converter to get well and truly HOT, thereby "clearing it's throat"
3. Closes down EGR, and allows the engine to breath pure air for a few seconds.

These are all good things for long term fuel economy.

(Sort of runs counter to logic, doesn't it?)

Hope it helps!

Good luck!


 

think diesel

Veteran Member
Joined
Jul 20, 2000
Location
Northern Virginia
Your friend is shifting WAY too friggin' early. He is probably stressing his drivetrain more than you are.

As a general rule of thumb, you want to shift just north of the peak torque (1900 rpm) for maximum fuel mileage and you want to shift just ahead of the peak horsepower (3750) to attain maximum acceleration.

Neither one of you is shifting for maximum fuel economy, and your friend is coming close to lugging the engine which puts an unnecessary amount of strain on the internal components of the engine.

You are driving in a more sensible manner, in my opinion. Your friend would get the same fuel mileage he is now by shifting at around 2000 rpm and his car would probably appreciate the change in his behavior.
 

GoFaster

Moderator at Large
Joined
Jun 16, 1999
Location
Brampton, Ontario, Canada
TDI
2006 Jetta TDI
Changing out of first as soon as possible is okay (first is too short anyway) but beyond that, it's better to keep the revs up a bit when the engine is under load.

Crankshaft and rod bearings use an oil film to keep the moving parts apart. I won't get into the exotic theory of hydrodynamic lubrication here, but basically there is a relationship between oil viscosity, the "shearing rate" (difference in speed between the two surfaces) and the amount of load that the bearing can take before the oil film breaks down and you have metal-to-metal contact.

Put simply, within certain limits, the higher the shearing rate (= engine speed), the higher a load that the bearing can support.

The owners manual of my car says to shift down when the revs go below 1500, and that's what I do: keep the revs above 1500 any time the engine is under load (idle or coasting down is fine; engine load is negligible). And I try not to apply FULL load unless above 2000 rpm.

In addition to this, all piston engines don't deliver power smoothly, they deliver it one cylinder power stroke at a time. There's a vibration damper in the flywheel/clutch to absorb some of this, but it will only take so much. Believe me, at 1000 rpm under load, every power stroke is being transmitted as a shock to the gearbox. At 2000 rpm same power output (i.e. lower torque output), the shocks come more frequently and less violently, so then that vibration damper has a hope of absorbing most of them. Higher revs mean LESS stress on the gearbox.

P.S. mbciii is referring to an "Italian tune-up". I don't need to consciously do those, as they are a routine part of my driving


Brian P.
'96 Passat TDI mit UPsolute
 
M

mickey

Guest
Your friend's EGR valve is open all the time. His intake will look like hell.

If you shift at about 2250, give or take, the next gear will be right on the torque peak at 1900. I think that's the best way to "keep up with traffic." 3500 is the right shift point for maximum acceleration.

-mickey
 

slickfisher

Well-known member
Joined
Apr 7, 2001
Location
Asheville, North Carolina
I think both you and your friend are wrong. You'all are at the opposite ends of the spectrum, er powerband. Your friend is shifting way too early- just read the manual, you got one of those didn't you? It warns about lugging below 1500rpm. I suggest trying to keep the tach between 1900rpm and 3000rpm unless maximum accel is needed in which case its ok to run it up to 3700 or so although I don't know which shift points yeild maximum acceleration. It ain't a Cummins and it ain't a VTEC. Enjoy.
 

Davin

Top Post Dawg
Joined
Jan 4, 2001
Location
L.A.
TDI
2001 Golf GLS 5spd blk/blk
Push right pedal to go, left pedal to stop.

-davin
 

mycruiseagent

Vendor
Joined
May 2, 2001
Location
Zephyr, TX
TDI
Jetta GL, 2002, Galactic Blue - R.I.P.
<BLOCKQUOTE><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><HR>Originally posted by TajCat:
So, any advice on driving an automatic? No, get up off the floor and stop laughing, I'm serious.<HR></BLOCKQUOTE>

I can't remember the source - but the rule of thumb I learned years ago (probably early 80's) to get best fuel economy from a 4 cylinder gas engine car was to use about 3/4 throttle to get to the shift point of about 2000 rpm (not that I actually ever shifted that soon)
. The idea being to get to the highest gear used as soon as possible without going to full throttle. This of course had to do with carburetors and gasoline, so I'm not sure if it still would apply directly to the TDI. So with an automatic, the same reasoning would indicate applying enough of the GO pedal to accelerate briskly without causing the transmission to stay in the lower gear any longer than necessary. What that level is would depend on the programming of the transmission.
 
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