TDI   -   FAQ
Bron: de FAQ van de tdi club com

N.B. Deze FAQ is ontwikkeld in de VS in de jaren 1995-2003, en is gebaseerd op Amerikaanse TDI's.

Algemene FAQ
  1. Typen TDI motoren
  2. Koude start
  3. Warmrijden
  4. Schakelen
  5. Prestaties
  6. Noise, Vibration, and Smell
  7. Longevity and Reliability
  8. Brandstof verbruik
  9. Fuel Availability
  10. Onderhoudskosten
  11. Can I use a remote car starter?
  12. Where do I find a good mechanic?
  13. Venting
  14. Things you may not know, but should
  1. 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.

  2. 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.

  3. Warmrijden - Omdat de TDI motor zo efficient is wordt de koelvloeistof minder snel opgewarmd dan bij benzine motoren. Een TDI motor bereikt zijn bedrijfstemperatuur niet door 'm stationair-draaiend warm te laten worden. Er is dus geen argument om de auto een paar minuten voor je vertrek te starten om op die manier een warm interieur te hebben als je wil wegrijden, want die wordt op die manier niet warm. Verwarmde zittingen (en standverwarming) zijn een waardevolle optie voor hen die in een koud klimaat leven.
    De beste manier om een TDI warm te rijden is te starten en meteen te gaan rijden. Het wordt aanbevolen om de eerste minuten netjes, rustig en voorzichtig te rijden totdat de temperatuurmeter van de koelvloeistof de bedrijfstemperatuur aangeeft. Als het op deze manier gebeurt verschilt het warm rijden niet zoveel van die van een benzine motor, maar het duurt merkbaar langer.
    Als je in de file komt te staan met een koude motor dan heb je een dilemma, omdat de motor stationair draaiend niet genoeg warmte produceert om de bedrijfstemperatuur te bereiken. Wat helpt is dan veel electrische apparaten aan te zetten, dus lampen en achterruitverwarming.
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  4. Schakelen - Veel is er al gezegd over wat het beste schakelmoment om zo economisch mogelijk te rijden. Het is bekend dat een TDI zich lekker voelt rond 2000 rpm, de turbo begint zijn werk begint te doen vanaf ongeveer 1500 rpm en komt op volle kracht rond de 2000 rpm. Bij 'normale' acceleratie schakel je rond de 2500 rpm naar de volgende versnelling en wanneer de kruissnelheid is bereikt zet 'm dan in een versnelling waarbij de motor tussen de 1500 en 2000 rpm draait.
    Voor maximum acceleratie, met een motor 'af-fabriek', schakel je rond 4000 rpm, omdat na dat toerental de kracht snel afneemt. Je wint trouwens maar heel weinig als je schakelt bij 4000 rpm vergeleken met schakelen bij 3500 rpm.
    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, lhere is limited availability of an automatic transmission with the TDI engine.
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  5. Prestaties - Er wordt vaak gezegd 'mensen kopen pk's, maar rijden met trekkracht'. Dit beschrijft volledig waarom met de de TDI motor zo prettig te leven is in het dagelijkse rijden, ondanks het schijnbare geringe aantal pk's!
    Een typische meerkleppige 2-liter benzine motor zal zijn maximum aantal pk's (waarschijnlijk ca. 120) hebben bij ongeveer 5500 - 6000 rpm, en zijn maximum trekkracht (ca. 120 lb-ft) ergens tussen 3500 en 4000 rpm, en zal bij 2700 rpm ongeveer 100 kmh lopen. In de hoogste versnelling op de snelweg zal de motor beneden zijn maximum trekkracht zijn, en bij die snelheid ongeveer 50 pk hebben. Terugschakelen is meestal nodig voor een snellere inhaalmanoevre, of om een steilere helling op te gaan. Als de auto een automatische versnellingsbak heeft dan zal de 'torque converter' vermoedelijk ontgrendelen als je een simpele helling op gaat om de motor op een toerental te laten draaien welk dichter bij de maximum trekkracht ligt.
    Bij de TDI motor is het maximum aantal pk's (90) beschikbaar bij 3750 - 4000 rpm, en maximale trekkracht (155 lb-ft) is beschikbaar vanaf 1900 rpm. De motor loopt 2100 rpm bij 100 kmh en heeft dan 62 pk ter beschikking. Hé, dat is meer dan de benzine motor, en niet zo'n klein beetje ook! Dus terugschakelen is niet nodig voor een inhaalmanoevre of om een helling op te gaan, zelfs niet op een stevige helling. En als de auto een automatische bak heeft zal het de torque converter niet ontgrendelen omdat het maximum aan trekkracht volledig beschikbaar is.
    Als je een sprint wedstrijd doet tussen een benzine en een diesel auto dan zal de benzine auto waarschijnlijk winnen omdat sprinten voor 90% gaat om de verhouiding pk's - gewicht. Maar wie rijdt elke dag zo?? De meeste mensen niet. Zelfs mensen die denken dat ze op die manier rijden, doen dat in werkelijkheid niet.
    Voor wat het waard is: diesel rijders (90 pk) met een standaard auto hebben 10 tot 12 sekonden nodig van nul tot 100 kmh (afhankelijk van het gewicht van de auto) en hebben een topsnelheid welke veel hoger is dan op de Amerikaanse highways is toegestaan. Met andere woorden, dat verschilt niet veel van de prestaties van een vergelijkbare 2-liter benzine auto. De auto's waar de VW TDI motor in zit zijn allemaal ontworpen om probleemloos een kruissnelheid van 160 kmh te rijden op de Duitse 'autobaan', en alle modellen kunnen zonder moeite nog sneller. Dus als je een diesel koopt in de hoop het aantal snelheidsbekeuring te verminderen, dat gaat niet werken!
    En voor degene die daar wel voor voelt zijn er verschillende manieren om de prestaties van de TDI motor aanzienlijk te verbeteren, die worden hier bediscussiëerd. Die veranderingen hebben geen invloed op het basis karakter van de motor - ze brengen meer pk's en meer trekkracht - en ze hebben meestal slechts een gering effect op het brandstof verbruik, tenzij je dat extra vermogen dagelijks en veel gebruikt. Een eigenaar van een New Beetle TDI doet nu iets meer dan 7 sekonden over 0 tot 100 kmh en hij heeft slechts gewone en gebruikelijke modificaties gedaan, niks exotisch.
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  6. 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.

  7. 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.

  8. 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!

  9. 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!

  10. 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.

  11. 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.

  12. 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.

  13. 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.

  14. Things you may not know, but should