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TDI FAQ
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2) General FAQ
- Types of TDI Engines - Various cars use
different engines which are generally described below. It should be
noted that this document primarily focuses on the 90hp 4-cylinder
engines, as these are the most common, and are the only ones seen
in North America.
1.2 litre 3-cylinder 61hp - This engine is used in the "3-litre"
(referring to fuel consumption of 3 litres per 100 km) versions
of the VW Lupo, Seat Arosa, Audi A2, sold in Europe. The injection
system uses the "pump-nozzle" or PD system, and the
turbocharger is a variable-vane type.
1.4 litre 3-cylinder 75hp - Used in various Polo-based models
sold in Europe. The injection system uses the "pump-nozzle"
system, and the turbocharger is a variable-vane type.
1.9 litre 4-cylinder 90hp (A3 type) - used in various models
sold until approximately 1998 in Europe and North America. Within
this document we will call this the A3 engine even though it was
also used in other models, because the most popular cars sold
with this engine were the A3-chassis Golf, Jetta, and Vento sold
from 1994 until early 1999. Not all model years were available
in all markets, and this engine was replaced by the newer type
(here called the A4 type) gradually over a period of years.
Other models sold with this engine include the B4 Passat (1995
- 1997), VW Sharan minivan, and various Audi models.
The injection system uses a distributor-type pump. On cars
with transverse engines, the A3 engine can be distinguished from
the later type by the spin-on oil filter on the front of the engine
facing down at an angle, the air filter housing is at the right
front corner of the car, and the two black plastic pipes to the
intercooler lead towards the left front corner of the car. There
are other differences, but these are the most easily visible.
The turbocharger is a conventional wastegate type.
1.9 litre 4-cylinder 110hp (A3 type) - used on the same models
as the 90hp but not available in all markets - in particular,
not available in North America. Visually it is almost impossible
to tell apart from the A3 90hp engine, except for the red "I"
in the TDI badges used on the car in various places. The
engine itself is identical to the 90hp model.
The turbocharger is a variable-vane type, and the injection
system uses a distributor-type pump which looks the same as that
of the 90hp model. Obviously there are differences in the
ECU, and in the plumbing and controls for the turbo, since the
turbo is not the same as for the 90hp model.
1.9 litre 4-cylinder 90hp (A4 type) - used in various models
available in Europe and North America from 1998 on, this gradually
replaced the previous engine as the car models were changed.
Within this document we will call this the A4 engine because the
most common application is the A4-chassis Golf, Jetta, Bora, New
Beetle, and various models from Seat and Skoda using the same
chassis.
The injection system uses a distributor-type pump. The oil
filter is a cartridge type, and sits in a vertical container on
the front of the engine towards the left of the car. On
cars with transverse engines, the air filter housing is at the
left side of the engine compartment and the two black plastic
pipes to the intercooler lead towards the right front corner -
exactly the opposite of the arrangement used on the previous model.
On North American models, the turbocharger is a variable-vane
type. On European models, the turbocharger is a conventional wastegate
type. The North American A4 engine is essentially a Euro 110hp
A4 engine but with engine controls optimized for emissions rather
than performance.
1.9 litre 4-cylinder 110hp (A4 type) - virtually identical
in appearance and specification to the 90hp except for the engine
controls; cars using this engine have a red "I" in the
TDI badges. Not available in North America.
1.9 litre 4-cylinder 115hp "PD" - again similar to
the A4-type engine but with the "pump-nozzle" injection
system. Although the peak power is only slightly more than the
110, maximum torque is much higher and the engine has lower exhaust
emissions. VW intends to gradually replace the 110hp models with
this engine. Not available in North America, reportedly because
the exhaust emission controls used on this engine cannot be used
with fuels containing greater than 50 parts per million of sulfur,
whereas at this writing (1999) fuels in North America can have
as much as 500 parts per million.
Models with this engine have badges with a silver "T"
and red "DI".
The injection system is the "pump-nozzle" type, and
the turbocharger is a variable-vane type. The lack of the
injection pump mounted on the front of the engine is the obvious
visual difference.
1.9 litre 4-cylinder 150hp "PD" - Few details are
available at this writing. Models with this engine apparently
will have badges with "TDI" in all red.
2.5 litre 5-cylinder - used in various larger models available
in Europe. The injection system uses a distributor-type pump.
2.5 litre V6 150 hp - used on various Audi-based models (including
the VW Passat) starting in 1998. Has 4 valves per cylinder,
and uses a distributor-type injection pump. The advantage
of using 4 valves per cylinder for a diesel engine is not so much
for better breathing, as it is to allow the injection nozzle to
be located precisely in the center of the combustion chamber and
oriented vertically.
2.5 litre V6 180 hp - differs from the 150 hp model only in
the use of common-rail injection instead of the distributor-type
pump.
3.3 litre V8 - used on the Audi A8 available in Europe.
-
Cold Starts - This is one of the big
questions that non-TDI drivers have: How well will it start in
cold weather? The answer is that they behave quite well. Volkswagen
was confident enough in the cold-starting ability of this engine
that there is no engine block heater designed to suit the TDI
engine. For those living in truly cold places - we're talking
Edmonton or Winnipeg cold, those in balmy Boston have nothing
to worry about - there are ways of making the block heater designed
for the previous 1.9 turbodiesel fit this engine, it's not easy
but it can be done.
Diesel engines operate on a principle of compression ignition,
rather than a spark ignition as in a gasoline fueled engine. The
air within the Diesel engine's cylinder is compressed much more
tightly than a gasoline engine, usually 2 to 2 1/2 times more
tightly. This high compression heats the squeezed air to a temperature
that causes the Diesel fuel to burn as soon as it is injected.
Cold temperatures suppress the tendency for self-ignition of the
Diesel fuel. "Glow plugs" are used to create a hot spot
within the cylinder to help force ignition. The glow plugs are
small electric heaters which are turned on before the starter
is operated. The amount of time required for these heaters to
obtain a sufficient temperature to ensure ignition depends on
the engine's temperature. When the coolant temperature is above
9 C, the glow plugs may not come on prior to starting. On cold
winter nights, they may take several seconds to heat up (7 to
10 seconds is typical).
Many measures have been taken to ensure reliable starts in
cold weather, but there are some factors beyond the control of
the car. More than one person accustomed to gasoline engines
has merrily hopped into the car during cold weather, stuck the
key in the ignition and turned it all the way to the "Start"
position (which prevents the glow plugs from operating!!!) and
then wondered why the car acts up. The proper procedure is to
switch the key to the "On" position and wait for the
yellow glow plug lamp to go out before cranking the engine. The
amount of time you have to wait ranges from none whatsoever (if
the coolant temperature is above 9 degrees C), to about 10 seconds
(if the car has been sitting outside in -10 C for some time).
If this is done, the engine normally starts with perhaps a second
of cranking, even at -10 C. Owners have reported starting
their engines at temperatures below -30 C, which is about -20
F. Better make sure the battery is healthy, at those temperatures
- but that's no different from any other car.
The other factor beyond the control of the car, is the quality
of the fuel. In Canada, diesel fuel must be provided to stations
"winterized" to expected outdoor temperatures as low
as -45 C in some areas. The most common source of problems
is when one purchases fuel at an out-of-the-way station, which
may go months between refills of their underground tank. Prudent
and experienced diesel drivers go to stations that have lots of
traffic during cold weather, to avoid getting a tank full of summer
diesel in the dead of winter.
The problem with summer diesel is that it "gels"
or "crystallizes" below a certain temperature. The TDI
engine is capable of operating at temperatures below what could
normally be expected for a given fuel, because the fuel filter
is heated by fuel being returned from the injection system. If
fuel gels up in the filter, the engine will generally start, but
won't have power to do much other than idle for a few minutes
until the fuel filter warms up ... but at least you'll get going.
It will only handle so much, though, and the car will not run
in -20 C with summer diesel fuel. Under very cold start-up conditons
(and this means in the -30 C range), you may need to wait for
several minutes with the engine idling before driving off to allow
the fuel to be warmed. Otherwise, power will be impaired or the
engine may stall as the injector pump will be starved for fuel.
Because of the long range of a TDi, when you are driving from
a warm to a cold climate it may be prudent to fill up with winterized
fuel in the destination area before the system cools down. If
you are in the unfortunate situation of a completely gelled fuel
system and the car will not start, the only cure is place the
car in a warm garage for a few hours.
For extra insurance, diesel fuel anti-gel additives are available
at truck stops and many auto parts stores. There are some additives
which can be added "after the fact" to a fuel tank which
is already gelled, and during extremely cold spells it is highly
recommended to carry a container of anti-gel additive in the car.
Using a portion of gasoline or kerosene in cold weather, as a
substitute for an anti-gel additive, is not recommended, because
these fuels do not have the proper lubricating characteristics
and cetane number.
It is normal to have somewhat reduced power and slightly higher
fuel consumption when using winterized diesel fuel.
-
Warm-up - Because the TDI engine is
so efficient, it puts less heat into the cooling system than comparable
gasoline engines. A TDI engine will not reach operating temperature
by idling. There is no point starting the car a few minutes before
you plan to use it in order to have a warm interior - it isn't
going to happen. Heated seats are definitely a worthwhile option
for those living in a cold climate!
The best way to warm up a TDI engine is to start up and GO,
after minimum essential warm-up. It's generally recommended to
drive gently for the first few minutes, until the temperature
gauge approaches the normal range. When done this way, the
warm-up period is not too different from that of a gasoline engine.
If one gets stuck in traffic with a cold engine, now there's
a dilemma, because the engine won't generate enough heat to warm
up. If this happens, one suggestion has been to introduce some
electrical load to make the engine work a little harder, like
the headlights, rear-window defroster, and heated seats if you
have them.
-
Shifting Gears - Much has been made
about what the best shift point is for maximum economy. It is
known that the engine "likes" running at around 2000
rpm, and the turbo starts kicking in at about 1500 and is going
full tilt by 2000. The author prefers shifting at about 2500 rpm
during normal acceleration, then when cruising speed is reached,
selecting a gear which puts the revs between 1500 and 2000.
For absolute maximum acceleration with a stock engine, shift
at about 4000 rpm, because power drops off quickly beyond this.
There is little to be gained by shifting at 4000 compared to shifting
at 3500.
For those not accustomed to manual transmissions, the TDI engine
is among the easiest to learn with. The engine quickly and automatically
builds up torque if the idle speed starts dropping, and the engine
doesn't race away like mad upon the slightest touch of the accelerator
pedal like many gas engines do. It's possible to smoothly let
out the clutch and start off from a stop, then shift to second,
and then to third, without touching the accelerator, and the car
will pull it!
For those who don't want to shift for themselves, there is
limited availability of an automatic transmission with the TDI
engine.
-
Performance - It has been said that
"people buy horsepower, but drive torque". This statement
completely describes why the TDI engine is so easy to live with
during day-to-day driving, despite the seemingly low horsepower
rating!
A typical multivalve 2-litre gasoline engine may have its maximum
horsepower (perhaps 120 or so) at 5500 to 6000 rpm, and its maximum
torque (perhaps 120 lb-ft or so) between 3500 and 4000 rpm, and
is probably geared to run about 2700 rpm at 100 km/h. In top gear
at highway speed, the engine is below its peak torque, and probably
makes around 51 hp at that speed. A downshift is usually
needed to make a quick pass, or to get up a steep hill.
If the car has an automatic transmission, the torque converter
will probably unlock going up moderate hills, in order to get
the engine closer to its peak torque.
With the TDI engine, maximum horsepower (90) is available at
3750 to 4000 rpm, and maximum torque (155 lb-ft) is available
at just 1900 rpm. The engine runs 2100 rpm at 100 km/h and makes
about 62 horsepower at that speed. Hey, that's more than
the gas engine ... by quite a bit, too! Thus, no downshift is
required to make a pass or to climb virtually any highway grade.
And if the car has an automatic, it won't unlock the torque converter,
because peak torque is right there already.
If you enter a drag race between these two cars, the gas car
will probably win, because drag racing is about horsepower-to-weight
ratio and little else. But who drives like that every day? Most
people don't. Even people who think they do - usually don't.
For what it's worth, owners report 0 to 60 mph times with a
stock car ranging from about 10.5 to 12 seconds (mostly depending
on the weight of the car) and top speeds well in excess of what
one ought to be doing on North American highways. In other words,
not too different from the performance of a 2-litre gas engine
in a similar car. The cars that the VW TDI is installed in were
all designed to handle autobahn cruising at 160 km/h (100 mph)
with ease and all models will exceed that easily, so if you're
buying a diesel in the hope of reducing the number of speeding
tickets you get, you'd better find a different excuse!
And for those so inclined, there are ways to significantly
boost the performance of a TDI engine, discussed elsewhere in
this document. These modifications don't change the basic character
of the engine - it makes both more power and more torque - and
they generally have little effect on fuel consumption unless you
use the extra power all the time. One owner has reduced the 0
to 60 mph time of his New Beetle TDI to a hair over 7 seconds
through suitable modifications - nothing exotic.
-
Noise, Vibration, and Smell - If you're
comparing the TDI to diesels of yore, there is no comparison.
It compares more favorably with 4-cylinder gasoline engines. It's
a little louder at idle with a little more vibration transmitted
to the passenger compartment (and it's worse when cold) but hardly
intrusive, especially after it is warmed up. It's actually
quieter at highway speed than equivalent gas engines, because
it's turning slower, just 2100 rpm at 100 km/h. It's especially
quieter during rapid acceleration when a gas engine would be buzzing
away at 5000 rpm while the TDI is loafing along at 3000.
Diesel noise and clatter are well isolated from the passenger
compartment and can only really be heard with the windows down.
Most true diesel-heads roll the windows down just to hear the
engine!
Diesel exhaust smell is noticeable outside the car after starting
a cold engine, but is considerably reduced compared to older diesel
engines. Fuel smells are only an issue when refueling, and
only if the pump is messy and covered with diesel fuel.
You don't want to get diesel fuel on your hands. In most
cases, it's possible to refuel without spilling any without special
precautions, but some owners suggest carrying some latex gloves
in the car if you have to deal with a messy filling station.
- Longevity and Reliability - These are well-known
strong points of diesel engines. There is the issue of the timing
belt, which must be changed religiously at the specified intervals,
or else. Aside from that, VW diesels have proven to be very durable
over the long haul. Some members of this forum tend to be "anal"
about oil changes and stuff ... but in a way, that's as it should
be, because diesel owners are generally in it for the long haul.
The diesel engine has certain factors acting strongly in its
favor, compared to modern gasoline engines. The engine itself
is very heavily constructed due to the compression ratio. Lower
exhaust temperatures than a gasoline engine extend the life of
the exhaust valves and the turbocharger. No spark plugs, no ignition
coil, no distributor, no plug wires, and diesel engines aren't
fussy about air/fuel ratio the way gasoline engines are. Although
the TDI has its share of electronics and sensors, virtually all
of those sensors are "non contact" sensors that work
either by magnetic fields, or by solid state electronics - i.e.
the sensors have no components to wear out. And the TDI lacks
what is among the most unreliable components of every modern gasoline
engine ... there are no oxygen sensors in the exhaust system.
It does have a glow-plug system (and some owners have had the
relay conk out) but this system is far simpler than the ignition
system of a gasoline engine.
-
Fuel Consumption - This is another
strong point of diesel engines. The TDI engine uses about 60%
as much fuel as an equivalent 4-cylinder gasoline engine. In Canada,
diesel fuel is less expensive than gasoline, so fuel costs can
be expected to be a little over half that of a similar gasoline
car. Using current fuel costs of C$0.65 per litre for gasoline
and C$0.60 per litre for diesel, and 8.0 L/100 km for the gasoline
car versus 4.8 L/100 km for the diesel car, you save $2.32 every
100 km. Payback of the extra cost of about C$1500 comes in about
65,000 km, which is less than two years for many long-distance
travelers and about three years for the average driver. Maintenance
costs are assumed to be about equal (which is about right) and
this doesn't take into account the fact that, at least in Canada,
it is virtually guaranteed that at the end of that payback period,
the diesel car will be worth MORE than the gas car ... possibly
by more than the original difference in price! (Example; at this
writing (late 1999), the going rate for a 1996 Passat VR6 with
say 100,000 km is about C$15,000 while the going rate for a 1996
Passat TDI is about C$18,000...)
In the USA, the situation is not quite as favorable, because
of generally lower fuel prices, and because diesel is relatively
higher priced compared to gasoline, compared to Canada. You can
do calculations similar to the above for your area.
Besides strictly economics, there are those who prefer the
characteristics of a diesel engine, regardless of the payback
period!
-
Fuel Availability - In most areas,
about one fuel station out of three or four has diesel fuel, and
diesel is always available at truck stops along major highways.
With the low fuel consumption, and the same size tank that the
gas cars use, the TDI cars have an impressive range, easily 1000
km (600 miles) or more. Availability of fuel is not an issue,
although as mentioned elsewhere, it's wise to fill up at stations
with a lot of diesel traffic, especially during cold weather.
Your VW has a fuel nozzle capable of accepting the nozzle at
large big-rig pumps, although you'd better set the pump at the
lowest feed rate possible to prevent a splash-back!
-
Maintenance Costs - The cost of maintaining
a TDI is not much different from maintaining a similar gasoline-powered
vehicle. You need to be a bit careful with oil changes,
because you need to use oil meant for diesel engines, so this
item tends to cost a little bit more. There's obviously
no need to do anything about spark plugs, plug wires, distributor,
or anything like that, so this cost item is eliminated.
The air filter needs to be changed once in a while, same as for
a gas engine. The fuel filter also needs changing, and it
costs a bit more than one for a gas engine, but it's only once
every 50,000 km or so - not a big deal.
The only pricey regular maintenance task is getting the timing
belt changed. After considerable indecision, VW seems to
have settled on a change interval of 90,000 km / 55,000 miles,
but check the owners manual for your particular vehicle as it
may vary. This is little different from the change interval
specified for most gas engines, but for some reason the job costs
more on a TDI. Do not try to skimp on this. Use the genuine
parts; change the tensioner too; change the serpentine belt and
the V-belt at the same time. If you buy a used TDI, then you can
either get a piece of paper proving the belt was changed at a
certain mileage and believe it (or not), or figure on getting
the belt changed to make sure. If it can't be proven that
the timing belt was changed, then assume it needs to be done.
DO NOT EVER neglect this!
Some owners have reported being charged exorbitant costs for
a "tune-up". Don't be suckered into this. Find out exactly
what the repair shop proposes to do in the "tune-up",
because there is very little to tune up. Most places will simply
do an oil change, and change the air filter and possibly the fuel
filter. Rarely will such a "tune-up" include cleaning
the air intake screen or the intercooler. Any owner with even
slight mechanical ability is capable of taking care of every one
of these tasks with the possible exception of changing the fuel
filter, and the price for a "tune-up" should reflect
this. Sometimes repair shops will attempt to cover up their lack
of diesel knowledge by specifying countless replacement items
which don't really need to be replaced. Injectors, glow plugs,
whatever.
As for unscheduled maintenance, who knows, time will tell.
There are forum members at or beyond 200,000 km / 120,000 miles
and still going.
-
Can I use a remote car starter? - In
general, the answer is "No", because remote car starters
generally do not have provision for the glow plug waiting period
in cold weather. Also, some manual transmission models do not
have a switch interlock to prevent starting with the transmission
in gear.
-
Where do I find a good mechanic? -
Boy, if we can find an answer for this ...
Normal maintenance on the TDI engine is not beyond the capability
of any competent mechanic. Even changing the timing belt can be
done by any mechanic who has half a clue. Unfortunately, there
are many mechanics out there who don't have half a clue. Some
of them even work at VW dealerships. Problems with mechanics doing
things wrong are not isolated to the TDI. All modern car engines
are extremely sophisticated and some repair jobs - particularly
"Check Engine light"-type repairs - should be left to
either a competent dealer, or to a mechanic who specializes in
the repair of that particular brand of vehicle.
Talk to other TDI owners in your area, and find out where they
go. IF you have an electrical or "Check Engine"-type
problem, make sure the shop you take it to has the computerized
equipment capable of monitoring OBDII engine controls.
-
Venting - In the filler neck of the tank,
in the "9 o'clock"" position is a little black button. This is a vent
relief valve that can be pushed with the fuel nozzle when "topping up"
the tank to squeeze in a few extra litres. The vent valve is designed
to prevent overfilling the tank. Overfilling could cause heat expansion
to push fuel up the neck and create a spill. The vent keeps an amount
of air in the tank until the cap is returned. The installation of the
fuel cap presses the vent button and allows air in the tank to move
up into the neck as the fuel in the neck moves down into the tank. Any
expansion will now burp only air instead of fuel.  Topping
up using the vent valve should be done only when the car will be driven
long enough to consume a gallon or so before stopping the engine. Don't
top off with the vent pressed and then park in the sun. For accurate
fuel mileage calculations always use the same technique when re-fueling.
Either always "top up" by venting the expansion chamber, or never vent
and stop refilling when the dispensing nozzle shuts off. That extra
half gallon or two liters of fuel squeezed into the expansion chamber
will make the trip consumption appear higher if this venting technique
is used intermittently.
-
Things you may not know, but should
- It is not recommended to let the TDI engine idle for extended
periods of time. Aside from wasting fuel, causing unnecessary
emissions, and not accomplishing anything (the engine won't warm
up at idle anyway), the turbocharger depends on having a certain
minimum level of boost pressure to maintain the condition of the
seals. Extended periods of idling may cause a certain amount of
oil consumption, and the oil consumption may clog the catalytic
converter. Some owners who have let their engine idle for a long
time report the engine running poorly for some time afterward.
And no, you don't need to worry about what's going to happen if
you get stuck in a traffic jam now and again, it's not THAT serious.
Just don't start the engine 20 minutes before you want to leave
in the morning every day, in the false hope of having a warm interior.
-
Old diesel mechanics may suggest mixing ATF with the fuel
to lubricate the injection pump. DON'T DO IT!
This may cause damage to the catalytic converter. Proper
additives are available to accomplish this, although even
those are probably not really necessary.
- Old hands may also suggest mixing a portion of gasoline with
the fuel in cold weather to prevent wax buildup. The owners manual
cautions against this procedure. Use proper additives which are
meant for the job, if necessary at all.
- Another questionable practice involves disposing of used motor
oil by blending it with diesel fuel. This is another thing which
sounds likely to damage the catalytic converter. Besides,
used motor oil contains extremely fine particles of solids which
may be fine enough to get through the fuel filter and into the
injection pump and injectors, where they cannot possibly do anything
good, and are a lot more likely to do something bad.
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All information Copyright © 1996-2002
Fred Voglmaier.
All rights reserved. This FAQ (Frequently Asked Questions) may not
be reproduced without written permission.
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