Petrol or Diesel?

For discussion of topics relating to the Driving Standards Agency Learner Test (DSA L Test) and contribution by ADI's (Approved Driving Instructors)

Postby fungus » Wed Feb 27, 2013 10:35 pm


What do you teach in, petrol or diesel.

The reason I ask, is that I have just taken on a new pupil who informs me that she has taken five driving tests, all of them in a diesel car. Her own car is a 1990s petrol Ford Fiesta, which she has never driven. Whilst she can pull away OK in my petrol Fiesta, she is obviously not over happy with it, and this becomes apparent when approaching hazards. She tends to almost freeze to the accelerator with what appears to be a fear that if she slows, she will have to stop, and then get going again. With a lot of talk through, I am encouraging her to plan ahead and ease off the accelerator to give her more time to plan and create space, therefore avoiding the need to stop. I have also been working on moving off very gently without using the accelerator to smooth out clutch control and build confidence when moving off. She will feed the accelerator in smoothly, but if there is a slight hill and there is a vehicle behind, then it all goes pear shaped. As with most learners, this is purely a fear of stalling the vehicle.

I can't help feeling that by teaching in a diesel, you do your pupil no favours, as most will buy a low powered petrol car as their first car, and then find that they have problems moving off, especially if their instructor has allowed them to become lazy, and pull away without using any gas.
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Postby exportmanuk » Wed Feb 27, 2013 11:01 pm


My youngest daughter had similar problems to begin with her ADI had a small diesel which was virtually impossible to stall but once she was over the basics I added her to my wife's small petrol car and to begin with it was a nightmare, Lots of stop start works on roads she was familiar with helped, and I think switching back and forth between the two has probably made her a better driver, more sympathetic to the vehicle.

Now however she has passed her test and we never see the wife's car. I have to use the bike to work like it or not :roll:
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Postby zadocbrown » Thu Feb 28, 2013 12:12 am


I agree there is an issue with this. The real villians are the instructors who encourage students to pull away with no gas. It's poor technique and will fall apart under pressure or in a less forgiving car.
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Postby martine » Thu Feb 28, 2013 7:34 pm


My training car is a Focus 1.6 petrol but I'm not full-time and I don't 'major' on learners in any case. I can understand why diesels are popular for ADIs though but of course they should be taught to balance 'gas' and clutch.
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Postby Rachaelink » Wed Mar 06, 2013 6:42 pm


Hi

I was going to post a new thread, but stumbled across this thread on my internet travels.

I am currently learning in a 1.2 l Petrol Micra, I am going along relatively well and just ironing out some fine details before booking a test. I have bought a car, due to it being a good deal and my mate having to sell the car in a short period of time. The car I now own is a Seat Ibiza 1.9 tdi.. slightly different I know.

So I am having the converse problem to most learners and struggling to get to grips with a more powerful diesel car compared to my tiny learner vehicle.

When I am approaching a roundabout for example I am told to approach in the higher gear, reduce speed, and then select second (if appropriate). I tried this in the diesel and it stalled before I could shift, quite a scary scenario at a busy roundabout. So it seems that my revs drop off a cliff and I would either shift to an interim gear, or engage the clutch earlier than I would be used to? Can you confirm what would be the best method?

In addition I was in a car park at a low speed, and without a foot on any pedal the engine suddenly delivered a thump of power, it didn't lurch, it drove. I assume this is some sort of anti stall? However I am not sure if I am doing something wrong.

I Just want to ensure I drive the new car well, safely, and have a bit of sympathy for the mechanics of the new car.

Thanks in advance for your help.
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Postby zadocbrown » Wed Mar 06, 2013 10:27 pm


Rachaelink wrote:Hi

I was going to post a new thread, but stumbled across this thread on my internet travels.

I am currently learning in a 1.2 l Petrol Micra, I am going along relatively well and just ironing out some fine details before booking a test. I have bought a car, due to it being a good deal and my mate having to sell the car in a short period of time. The car I now own is a Seat Ibiza 1.9 tdi.. slightly different I know.

So I am having the converse problem to most learners and struggling to get to grips with a more powerful diesel car compared to my tiny learner vehicle.

When I am approaching a roundabout for example I am told to approach in the higher gear, reduce speed, and then select second (if appropriate). I tried this in the diesel and it stalled before I could shift, quite a scary scenario at a busy roundabout. So it seems that my revs drop off a cliff and I would either shift to an interim gear, or engage the clutch earlier than I would be used to? Can you confirm what would be the best method?

In addition I was in a car park at a low speed, and without a foot on any pedal the engine suddenly delivered a thump of power, it didn't lurch, it drove. I assume this is some sort of anti stall? However I am not sure if I am doing something wrong.

I Just want to ensure I drive the new car well, safely, and have a bit of sympathy for the mechanics of the new car.

Thanks in advance for your help.


This is a common issue with turbodiesels. There are various ways round it.

For most situations just learn to dip the clutch as the revs reach idle, to prevent stalling, then continue as you've been taught. This is fine so long as it doesn't lead to coasting for an extended period - i.e. more than a few seconds.

In situations where this doesn't work well, an example would be when you are making a long approach slowing down gradually, you can take an intermediate gear to bridge the gap.

Another thing to consider is that you may want to make slightly different gear choices. Forinstance you have probably been taught to use 4th at 30mph, but 3rd may work better in your TDi. If so, it will also ease the problem you came here with.
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Postby martine » Wed Mar 06, 2013 10:50 pm


Welcome and interesting choice of car for a new driver...is the insurance affordable? I digress.

Good advice from Zadoc...I had an IAM Associate with a Seat diesel and it was very long-geared. We ended up using an intermediate gear on the approach to roundabouts from high speed...so 2 gear changes (eg 6th - 3rd - 1st or neutral) rather then the ideal 1.

Part of being a good driver is adapting to make the best of a car's features. Don't fall into the trap of sticking with this technique in other cars - unless it's needed of course.
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Postby Gareth » Wed Mar 06, 2013 11:39 pm


Expanding on zadocbrown's comments ...

There's a range of 1.9 diesel engines fitted to the SEAT Ibiza from 1993 onwards; it might be possible that someone can give more specific advice if you can say which variant is in your car. The following comments are based on my experiences of driving various diesel engined cars, including our 1.9 Octavia.

Rachaelink wrote:When I am approaching a roundabout for example I am told to approach in the higher gear, reduce speed, and then select second (if appropriate).

This very much depends on both the car and the size and layout of the roundabout. In a typical 30 mph limit I'd tend to be using 2nd gear whenever my speed falls below about 28 mph, and only using 3rd when I can keep close to the speed limit for an extended period.

If you are approaching in a higher gear with the aim of changing to 2nd for the roundabout, (if it is clear to continue), then I imagine you are thinking of higher speeds (and limits).

I tend to use 3rd or 4th as an intermediate gear. If there is a good chance of needing to stop I'll aim to use 3rd and will declutch at engine idle speed to avoid judder. This would be about 20 mph, which I find to be comfortable - I don't like declutching at significantly higher speeds as a prelude to stopping.

Rachaelink wrote:I was in a car park at a low speed, and without a foot on any pedal the engine suddenly delivered a thump of power, it didn't lurch, it drove.

In many cars, not just diesels, it is handy to be able to vary the speed by modulating the clutch. It is rare that a car will drive smoothly with the clutch up and no accelerator applied. There is a minimum speed the car will travel with the clutch up and no accelerator, and often you want to be going slower, especially in car-parks.
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Postby michael769 » Thu Mar 07, 2013 3:01 pm


Rachaelink wrote:In addition I was in a car park at a low speed, and without a foot on any pedal the engine suddenly delivered a thump of power, it didn't lurch, it drove. I assume this is some sort of anti stall? However I am not sure if I am doing something wrong.



This is indeed the result of the ECU's (Engine Control Unit) anti-stall function kicking in - the extra low speed torque (pulling power) provided by a diesel engine makes it much more noticeable than in a petrol car and it can be a little disconcerting until you get used to it. In many modern cars it is possible to get them to "drive" themselves along at a steady speed without your putting your foot on the accelerator - but this is not recommended as you are not really exercising full control over the vehicle!.

If the anti-stall is trying to maintain a higher speed than you want - it is a sure sign to change down a gear, if in first you will need to slip the clutch a little to maintain control at a lower speed (braking against the anti stall is not good for the car and can make it hard to control).

Many turbo diesels are geared in a manner that requires a lower gear to be selected than you might be used to in a petrol car - for example try experimenting with driving in 3rd at 30mph and 4th at 40mph and see if the car feels more controllable and responsive. An easy way to tell if it is more controllable is that you may find yourself using the brakes less.

When approaching junctions and roundabouts on higher speed roads you may find you have to drop the clutch sooner than you are used to - if you feel that the amount of time you are coasting is excessive consider selecting an intermediate gear.
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Postby Rachaelink » Thu Mar 07, 2013 9:41 pm


Thanks for all the replies, it has put my mind at ease to an extent. Its just so at odds to what I have been told, though I agree that this is not a prescribed method for every car. I certainly want to ensure I get the best out of my new car, and do not put undue pressure on it through not having sympathy for how it works.

With regards to the query regarding insurance, its actually surprisingly cheap to insure. I am 30 ( late starter I know), but it was only £150 p/a more than a Hyundai i10 I was looking at initially.

Its a 09 plate 1.9 tdi sport and has really low mileage, with a full service history. I was offered the vehicle at trade price and felt that it was too good a deal to turn down. I hope I grow in to the car, and in a few months will be glad I did not opt for a tiny vehicle. Only time will tell.
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Postby fungus » Fri Mar 08, 2013 11:36 am


Hi Sarah,

As my previous car was a Seat Ibiza 1.9 TDI (105ps), I can only agree with the comments made by others. You will need to use intermediate gears like 3rd or 4th, and some tight turns will require 1st in order that the engine revs do not drop too low and allow the engine management anti stall system to raise them again, giving you a power surge as you come off the brakes. You will find that if you allow the revs to drop too low, the car will start to judder.

You might also find the brakes a bit sensitive, but having said that, you will find that the ABS does not activate easily under emergency braking, in fact in my experience, the brakes on the Ibiza are very good. One problem that Ibizas' are prone to is brake light switch failure. If the engine management and glow plug lights come on together, check that you have brake lights, as every time this happened to me it was a faulty brake light switch, which is not expensive if you go to a non franchised garage and have it checked.

I can only say that I was very happy with my Ibiza. It certainly had a better gear box than my Ford Fiesta.
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Postby Rachaelink » Fri Mar 08, 2013 2:23 pm


Thanks for the post, I assume I am Sarah? :wink:

This describes what I have been experiencing.

I am driving the car where I feel it is happy in terms of revs etc, however the people accompanying me often encourage me to take a higher gear. They are used to petrol and I dont feel that I have enough experience to really question them. However I am concerned that this might affect my fuel consumption?

With regards to the brakes, they are good, but they are scary when you first try them, they are so sensitive. All in in all though it seems like a great wee car.

Thanks for the tips though I will def keep that in mind.
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Postby Ancient » Fri Mar 08, 2013 3:00 pm


Rachaelink wrote:Thanks for the post, I assume I am Sarah? :wink:

:lol: Two people with different female monikers have posted on the forum lately - it gets the boys all confused and flustered! :P
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Postby michael769 » Fri Mar 08, 2013 3:46 pm


Rachaelink wrote: However I am concerned that this might affect my fuel consumption?



Driving style, of course affects fuel consumption, but that can be both good and bad. In general a higher gear will reduce fuel consumption, but not always. A high gear can lead to the engine straining, and also promote excessive braking both of which increase consumption.

if you are concerned I would suggest monitoring it, if you don't have an in car fuel computer keep track of how much fuel you are putting and and your mileage.

If you car to share where you live, perhaps there will be a member near you who is willing to have a look at your driving and provide some "expert" opinion?
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Postby fungus » Fri Mar 08, 2013 3:59 pm


Appologies Rachaelink, having a senior moment. :oops:
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