How to drive a diesel

[Rawas]

Jim 314
Impressive, are you a mechanical engineer?
The debate between diesel and petrol engines preferences is a hot topic on another Volvo forum. I wish you contribute.
Also, how would you rate your 2007 XC90 reliability so far?
Regards.

[Jim314]

My wife's 2007 XC90 3.2L inline 6-cylinder naturally-aspirated petrol has been completely reliable, but the fuel efficiency is low compared to an XC90 with a Volvo diesel. On the other hand the 3.2L petrol handles short trips well. I expect that over the lifetime of the vehicle the maintenance costs will be much less than for a modern turbo diesel with diesel particle filter or a modern turbocharged petrol engine. In 5 years of ownership from new we have only put 40,000 miles on it. I just had the engine air filter element changed for the first time.

This is a modern high compression petrol engine and I am surprised that it does not get higher extra-urban fuel efficiency. On one long highway trip of over 500 miles we did get 34 mpgUK (28 mpgUS, 8.4 L/100km), but never approached that before or since. We were travelling from west to east in Texas and maybe we had a strong west wind behind us. Usually we get about 27 mpgUK ( 10.4 L/100km or 22.5 mpgUS) on the highway. In urban use on tanks with all short trips, we get as little as 16 mpgUK (18 L/100km or 13 mpgUS).

When the original tyres wore out I replaced them with Michelin Energy tyres 235/65-17, but this had no noticeable effect on extra-urban mpg.

Volvo has not offered diesels for the US market for at least 10 years. I don't think Volvo diesels are available in Canada, not sure about Mexico. I think Volvo did not want to go to the expense of engineering these engines for the North American environmental requirements.

PS I am a retired US civil servant (US Food and Drug Administration) with degrees in physics and biophysics. I am well aware that my knowledge of automobile technology is rudimentary compared to a professional engineer or really knowledgeable amateur enthusiast, and it was obtained by general reading and internet surfing.

After retiring from the civil service I did work for a time as an automobile crash reconstructionist after getting some formal training in that area.

[Bernard333]

Originally Posted by Jim314

How do Volvo diesels (manual or automatic) perform in descending mountains compared to Volvo petrol engines?

I have driven both ways over the St Bernard pass quite a few times mainly to save paying the tunnel toll but also because its a nice drive but takes an extra few hours to go over the top rather than through it . My car is a Euro 3 V70 D5 manual , never had a problem with heat build up or brakes fading on the way down mainly because engine braking is good and thats with a fully loaded car . Its 8000 feet as you go over the top and fairly steep on each side but it cant be that difficult as diesel powered coaches full of tourists easily manage the same route and I would assume they need more assistance from engine braking than a car ?

[Jim314]

Diesel powered coaches have 'Jake' brakes which automobile diesels do not have. See http://en.wikipedia.org/wiki/Compres...e_engine_brake.

Your comment on your experience with your Euro 3 V70 D5 manual is what I wanted to know about. So the Volvo auto diesels do have good engine braking on descent.

[rippedoffagain]

Originally Posted by Jim314

I think fuel is priced unreasonably low in the US and this is one reason why so many Americans buy fuel guzzlers. For their part, the Europeans were willing to drive air polluting diesels to obtain great mpg.

Please don't take this the wrong, because I take your point but I think its wrong. But then I could be wrong, but...

I thought Europe in general, especially western Europe and Britain, has always been way ahead of the US in terms of fuel efficiency AND comparative cleanliness of emissions.

I think the EU (or the EEC or one such collective over here) have pushed through so many laws in the last 25 years to give us lower emissions. For example, I think all over here registered after some point in 1992 had to have a catalytic converter. I think it was emissions laws rather than anything else that practically eliminated the carburettor and mechanical points over here, in favour of much more efficient fuel injection and electronic ignition.

Like I said, I could be wrong. Its been known

[Jim314]

It has certainly been the case that the US lagged behind Europe and Japan in promoting fuel efficiency in automobiles. Motoring fuel has been costly in Europe, but cheap in the US. I pay about $1US per litre for the 95 RON petrol I put in our Volvos (~ $4US/galUS). The American media and public are outraged if the price of gasoline (petrol) gets to $4/galUS.

But it has been my impression that the US was ahead of most or all of Europe in regulating automobile tailpipe emissions. For example, I thought the US was ahead of Europe in requiring unleaded petrol and catalytic converters. But this is something that should be determinable and not merely a matter of opinion.

The way I had it figured was that it was US government policy to provide the American public with cheap petrol to enable commuting in private autos and to promote employment in the auto manufacturing and servicing industries.

[Jim314]

I started driving at age 16 in 1960 and so my driving career has spanned the change from leaded petrol to unleaded. I remember well the objections of some of my fellow Americans to any changes in emissions limits which would decrease performance or fuel efficiency or would increase the cost of fuel.

Didn't Jaguar offer an engine with a considerable following in the US among wealthy enthusiasts that could not be made to meet US emissions standards? This may have been during the leaded petrol days in the 1960s or 70s.

The first widespread introduction of catalytic converters was in the United States market, where 1975 model year gasoline-powered automobiles were so equipped to comply with tightening U.S. Environmental Protection Agency regulations on automobile exhaust emissions.
http://en.wikipedia.org/wiki/Catalytic_converter

[SourDiesel]

Diesels have no engine braking? never driven a defender down a steep incline with 'feet off' then! remember diesel fuelling is controlled significantly better than petrol fuelling. this combined with higher compression ratios gives much better control of engine speed by the ecu.

[Jim314]

Cutting off fuel does not cause engine braking. It is the air pumping resistance on the motion of the pistons that causes engine braking. Diesels, due to no restriction of intake air, don't have any pumping resistance. The lack of pumping resistance is one of the reasons diesels are more efficient than petrol engines.

The Land Rover Defender must have an automatic control system which detects a downhill attitude and automatically applies the friction brakes. Alternatively, the Defender may have an exhaust restriction or special hill descent throttle which engages and provides engine braking.

[PeteB1]

Originally Posted by Jim314

What is a 'Defender'?

Defender

One might have once called it the British Jeep.