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Home › Features › Doctor Diesel › Doctor Diesel

Doctor Diesel

Posted on September 27, 2019 by Steve Dawson — No Comments ↓

Deep sigh of satisfaction

Dear Doc,
With regard to my Qashqai (Issue 390) noise problems and the back axle replacement, the garage has now replaced it and this apparently also cured the persistent rattle. As for the hissing noise, that has also disappeared, but whether it was linked to the axle problem, or whether it’s a cold/warm weather issue, I just don’t know. My Qashqai now goes well, and so far has been trouble-free.

As to whether it was ever involved in an accident, as I half wondered with it being untaxed for some nine months, I cannot tell. I’ve been around cars for years and if it has been in an accident, then they’ve done a damn good job in repairing it! A mate of mine who repaired accident damage years ago, told me some of the signs of repaired cars and I can’t see any of these on this car. Thank you very much for your interest and concern though. 

On a rather different matter, I read with interest Diesel Car’s Top 50 cars for 2019, but I noted that there was no sign of the Qashqai. Is this an oversight I wonder, or is it that the car, although apparently very popular with the public, is not so popular with the motoring journalists? In fact, Nissan didn’t appear at all in the honours list. Once again, thank you though. It’s an old cliché, but I do enjoy your pages, and they are amongst the very first that I always go for, along with the “Our Cars” pages. 

Regards,

Max Hayman

Max,
Many thanks for the update. Maybe my comments regarding potential action were possibly somewhat extreme, and I am really glad that you seem to have had a good result from the garage, following the rear axle replacement. I am not really sure why the Qashqai did not make it at least into the Top 50, although the issue may have been clouded by non-availability of the new model 1.7 diesel variants, which is probably the preferred engine choice for many people. I do have to say also that the latest Qashqai does not have the best of reputations for reliability. It is very popular with buyers, judging by the number of them that are sold, but not quite so much with owners! Your niggling problems are perhaps examples of that situation?

Anyway, I am certainly pleased that you are now happy with the car. 

Very best regards. So glad to hear that you still enjoy my senile ramblings! 

Doc


A noise annoys

Hi Doctor,

The noise from the tyres on my BMW X1 is so ridiculous that I am seriously considering changing the car for something that promises to be quieter. My test drive on very good surfaced roads local to the dealership where I bought it revealed no problems in this regard. However, having read about tyre noise from run-flats often fitted as standard to the BMW X1, I specified non-run-flats when I purchased the vehicle new in 2017, and was pleased to see that Bridgestone Turanza T001 225/55 R17’s had been fitted when I collected the car. It didn’t take many miles in the car before I realised that my plan had indeed back-fired, with the unacceptable high levels of tyre noise. Back at the dealership, and following a test run, they announced that the noise levels were acceptable. 

I understand though, from reading many car magazines, including Diesel Car & Eco Car, that the subject of noise is only addressed briefly within the general text of any new vehicle review. However, Diesel Car & Eco Car, Issue 389 of June 2019, describes the new Mercedes-Benz B 200 d  AMG Line in the final paragraph as “hugely refined with low levels of road and tyre noise, and little wind flutter.” Unfortunately, though, the B-Class is just too small for me! My X1 is just the right size, it performs very well, it is economical, looks great and is just the right height for access with my dodgy hips.

Is it possible to have guaranteed soundproofing fitted to my existing car? I know it would possibly be expensive, but much less than purchasing a new car with unknown, non-specified sound levels.

In my after-sale survey, issued direct to me from BMW, I strongly expressed my disappointment and I would expect many others have done the same in regard to tyre noise. A facelift X1 has just been introduced, and I am wondering if perhaps this noise issue has been addressed, because it’s a great car let down by this irritating noise. Many thanks and regards, 

G Beardmore, Staffordshire

Hello Graham. 

Reference the BMW X1 tyre noise, which you had read about and, just as I would have done, you thought by avoiding low profile run-flat tyres you would escape the noise problem. Unfortunately, it seems not to be the case, and that the whole body structure, along with poor noise insulation measures, seems to indicate that road noise is endemic with the X1 model that you bought, although I still suspect that tyres have a considerable influence on the situation.

You may be well aware of the tyre labelling system, where one of the three specified pieces of data for any given tyre is a noise rating. We should be aware, though, that this is actually for “drive-by” noise measurement, as measured by a noise meter placed at a specified distance from the car driving by at a specified speed and distance away, and on a specified standard road surface. It is primarily directed at addressing the environmental noise impact, and not at in-cabin noise, to which it will be loosely, but certainly not that precisely, related. For instance, a car that has effective wheel arch liners can actually disperse tyre noise externally by reflection, and thereby reduce cabin noise, but at the expense of the measured external noise!

But some tyres are undoubtedly fundamentally quieter, and less harsh riding, than others, and Goodyear EfficientGrip are some of the best, having ratings of 68dB in your size, compared with the 71dB rating of your Bridgestones, which do tend to be noisy, and reflected in cabin noise. The Goodyears would be significantly, if maybe not amazingly, quieter than the Bridgestones, which are also notorious for getting noisier as they wear. Another good low noise tyre is the Yokohama Advan Fleva V701 – even quieter at just 67dB, and aimed rather more at performance cars than the Goodyears.

Presuming that you have not yet had cause to replace the original Bridgestone tyres, a successful switch to a set of Goodyears or Yokohama for under £500 could make you a very happy man, and save you the significant cost of a car change. Is there any guarantee that the new X1 is quieter? It’s the sort of thing that might well have been attended to, without BMW admitting to previous shortcomings. But best see if you can get a test car as soon as they are available, and listen for yourself, although again the tyres fitted to the test car are critical. If you haven’t done that many miles in the existing X1, which would seemingly be the case if you have not yet needed to replace any tyres, you don’t really need to change cars, do you? A good BMW engine, that is serviced regularly, is surely good for 100,000 miles plus, as should be the rest of the car. 

Hope this is of some help to you, but please come back to me if I can be of any further help!

Best regards, 

Doc Diesel

P.S. Noise insulation of the car can help. Insulation under floor mats, in the cargo area, and on the inside of the doors. Do the doors sound tinny when you rap them with your knuckles? If so, then some insulation could be effective, but not necessarily a total cure.

Hi Doctor

Many thanks for the lengthy reply – very useful and informative. With 22k on the clock, the existing tyres have only a few thousand miles left before I need to change all four, as I had them changed ‘front to rear’ last year, just before the winter, to achieve better grip on the drive wheels. I will take your advice and have a full set of Goodyears/Yokohamas fitted in a couple of months. It’s very good of you to go into so much detail, I do appreciate it so much and will keep you updated and informed of the outcome. 

Many thanks and best regards, 

Graham B


Diesel dilemma

Dear Dr Diesel, 

I have been driving diesel cars for what now feels like a very long time, and I absolutely love them, so I really don’t want to be forced back into a petrol engined car. However, our current ‘Government’ seems to hate diesel power with a passion.

As you may possibly recall, I have a Skoda Octavia as a family car, but I also have a very old Vauxhall Corsa as a work car. Brim-to-brim tests have shown that the Corsa will happily do 63 to 65mpg on journeys that include a mix of fast A-roads and motorways. When working in the London area, the Congestion Charge has forced me to use the Octavia, though. On a quiet run to Gatwick, the Octavia has averaged 67mpg, whilst running the same journey in reverse in the rush hour has yielded 58mpg, due to the heavier traffic. Anyway, I will soon have to change my work car and, given the current uncertainty, I am very unsure. The Government will be forcing urban areas (such as where I live) to introduce a London-style Congestion Charge, the exact details of which are not yet clear, but what seems certain is that it will be designed to ‘tax’ the motorist. I think I can rule out a battery powered vehicle, because they don’t have the range for the sorts of journeys that I am expected to complete. And, whilst the Teslas have access to a very well-developed set of fast chargers, none of the more affordable cars do. I would like another diesel, but even the cleanest of diesels are seemingly likely to be heavily penalised by the current ‘government’. I am actually wondering if a plug-in hybrid might be a possibility?  A vehicle that gives 200mpg, and also has a 600-mile range, sounds very attractive! My concern though is what happens on a long motorway run, when the hybrid battery has been depleted? It then ceases to be a partly battery powered vehicle, and becomes instead a pure petrol-powered vehicle dragging a heavy, useless battery. Does it drop down from 200mpg to maybe 40 to 50mpg? 

Best wishes,

David Price. Wolverhampton. 

P.S. Our five-year old Octavia just sailed through its recent MOT test, with a 0.00 score on the smoke test.

Hello David, I remember the name very well, even if not the cars. To your current dilemma, I hope that I am right in concluding that the Corsa is a diesel, and therefore specifically the 1.3 MultiJet engine of Fiat origin. A fine engine, although a bit prone to DPF problems when used only for short runs. That engine was apparently designed by Fiat for a 120,000 miles plus life, or 200,000 kms. But then the Octavia has proven to be not far behind on fuel economy, hasn’t it? 

If you make sure that you get the very latest and cleanest diesel – or any Euro-6 diesel for that matter, as they are not splitting hairs yet, and probably won’t ever, regarding the confusing sub-sections of Euro-6, like Euro-6d and Euro-6d temp, with regard to admission to low emissions zones. Surely they would not dare try to sub-divide Euro-6 in such a way? So, it seems, as far as the foreseeable future goes, that Euro-6 diesels are not likely to be victimised, even if some of the earlier ones were a lot higher in real life NOx emissions than the very latest ones.

If you did want to cover yourself though, a switch from the Corsa to any cheap Euro-5 or -6 petrol car, such as maybe a small car – like a petrol Corsa! – would leave you totally safe for any city travel without impediment or charges. What you really need (and Britain needs!) is a small, cheap, light, plug-in electric vehicle with a range of 100 miles or so, which would suit you fine probably – but nobody wants to make such cars – no profit! – even though they are desperately needed to clean up city pollution. Would a second-hand Renault Zoe be worth considering as a runabout, and for such city business trips?

But for longer journeys, I think you should look at alternatives and stick to diesel power David, as undoubtedly many others will. Out on the open road, one of the latest clean diesels saves on CO2 emissions compared with petrol or petrol hybrids, which do a nice green job in towns and cities, running on battery power, but as you say do nothing for the environment or fuel economy once their batteries are discharged after plug-in charging. Beware of the temptation of cars claiming huge mpg figures, derived from short test cycles that allow the electricity to make a significant effect. I well recall testing a Golf GTE on a hot day, with full air conditioning required to cool down a hot car, and I found that within 10 minutes the battery was discharged, and thus I was then just running on petrol. As another journalist reported “However frequently I plugged it in, and however gently I drove, and however I tried to fiddle the figures, I never got near the official 157mpg. Based on real world experience, you can get as much as 60mpg if you give it a 4-hour charge every 100 miles, rather than the 40mpg you will get without any plug-in charging.”

Maybe 40 to 50mpg is possible on a long motorway run? You might hit 50mpg at a steady, honest 70mph with one of the best petrol hybrids, instead of 60mpg plus in a good diesel, but 40mpg is more like it, and you have all that technology and weight doing nothing for you on such a journey. 

I hope that this gives you some helpful thoughts David. Do please keep me posted with your thinking and take plenty of time to research things in depth when buying. And take note that diesel depreciation figures are still strong, and that used diesel prices are still holding up quite well. 

Best regards,

Doc


Emissions concerns

Hello Doctor. 

Amidst all the euphoria regarding electric cars, I have noticed some reports that their noxious emissions are far from insignificant. Apparently tyre wear and braking have been identified as making a significant contribution to all road vehicle particulate emissions, and road surface wear is also a significant source of particulate pollution. Can you fill in the facts and offer some figures relating to this issue, please Doc? 

Norman Willis,

Stoke

I will do my best Norman, and thanks for your message. Figures are difficult to come by though. It isn’t just air pollution that is in question here, as authoritative research has revealed that around 5 to 10 per cent of the plastic and polymers accumulated in our oceans may be derived from tyre wear alone (and that comes from bikes as well as cars, vans and buses), as much of it ends up in our rivers that then discharge into the sea. That’s a real eye-opener, as the stuff just doesn’t go away, as we know well from all the plastics that we are now discovering in the oceans, some lying at the bottom of the seas where they will remain for centuries. Tyre derived particulates have presumably been ending up in our oceans for as long as the car has existed though, and those of us who can look back fifty years and more can remember how quickly tyres used to wear back in those days! But then come to think of it, there were a lot less cars around then, compared to now!

In the more general picture of air pollution, braking system particulate emissions are assessed as possibly being as high as 50 per cent of direct vehicle related PM10 emissions, the larger particles of the particulate size band, on the borderline of being visible. The picture is a little clouded though by the inclusion of what they call the “re-suspended” particulates that are stirred up from the road by the passage of any vehicle. It is important that this area is fully investigated, as it is apparently being right now, since many of the components of such friction-derived particulates are vastly different in chemistry and health risks from exhaust emissions. It would be an error on the grandest scale if the specific dangers of these non-engine emissions were not identified. Without this, the specific health hazards of other emissions, like exhaust, might turn out in time to have been wrongly blamed for some health issues. Realistically though, electric car in-use emissions should be much reduced in all areas, since they use less friction braking, due to the regenerative braking systems employed. Their tyre wear, though, will probably be very similar to any fossil fuel car used in the same way, and the re-suspended particulates, which are not necessarily derived from cars themselves, will also be unchanged. 

But many issues are clouding the picture. Congestion in cities is a significant factor in urban pollution, and here the electric cars score well, since they produce no emissions at all when stopped, and no high emissions during acceleration, and few in deceleration. Bearing in mind that emissions are traditionally measured as gaseous or particulate matter emitted per unit of distance travelled, the slower the traffic moves, the higher the emissions when measured that way. Along with the undeniable benefits of excluding the dirtiest cars (many diesels!) from urban centres, traffic speeds should, on paper, be improved with reduced congestion. So, the exclusion strategy amounts to a double-edged effect in reducing emissions – as long as the alternative means of transport are clean. But forcing people to use dirty taxis and buses with poor emissions control equipment isn’t any kind of answer, so both needs cleaning up as quickly as possible. I might add too that some of the highest polluters are large, expensive cars with large engines, and affluent owners, for whom zone charging represents little disincentive!

I may have strayed a little off-subject, but I think you will have the gist of my thoughts on the matter! 

Best regards,

Doc Diesel

 

 

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