Me and my better half are still getting used to the joys of a diesel but one interesting finding came up in conversation the other night.
To be honest we are trying to outdo each other on fuel economy (average per tank)
Where we live is not far from a main motorway that we both use.
When I travel on this road there is more traffic so the car spends more time warming up in traffic before motorway speeds are used.
But for my other half there is no traffic when she uses this road so the engine is still cold when running at motorway speeds.
So my question is, are diesels running at motorway speeds a lot less economical than when warmed up ?
Sorry for a rambling post
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I suspect there's less difference than you think in the degree of warmed-upness. Diesels produce very little waste heat when not under load, so your idling in traffic probably isn't warming the engine very much. The first winter I had mine, I used to drive it on a 3-mile cross-town route to work, often in heavy traffic, and the heater was usually only just starting to produce warm air when I got there. (A compelling case for heated seats, incidentally; once the weather improved, I cycled instead.)
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Not based on any science you understand but just on personal experience. On short traffic ridden runs my petrol car is rubbish on mpg but gets very much better once warm and over long distances at a cruise. My diesel car seems at least to care little how and when it is used. It bumbles along at more or less the same mpg in most circumstances.
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My diesel car seems at least to care little how and when it is used. It bumbles along at more or less the same mpg in most circumstances.
My findings too.
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The first winter I had mine I used to drive it on a 3-mile cross-town route ............ and the heater was usually only just starting to produce warm air when I got there. (A compelling case for heated seats incidentally; .............
A compelling case for having a petrol car!
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A compelling case for having a petrol car!
... or as on my E39, a diesel burning auxilliary heater. Job done.
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>> A compelling case for having a petrol car!
>>
It would take more than that to compel me to go back to petrol! Mind you, they are improving rapidly in the torque and economy areas where they have always been weak.
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We are trying to outdo each other on fuel economy ...
Which way? :-)
The diesels I have owned take 5 or 6 miles of driving before the thermostat opens, or perhaps 8 to 10 minutes running. At a guess this might be twice as long as a petrol engine. The newer second-generation DI diesels of 1.5 or 1.6 litres instead of 2 may take even longer. But I don't see why 'motorway speeds' are significant - if the engine is running at 1500-2500 rpm, what the car is doing makes little difference, other than the rate air goes through the radiator. And when the thermostat is shut, that is not very important.
But long ago I understood one reason tradesmen - especially delivery men doing frequent stop-start - preferred diesel was that the engine could be left idling at very little cost.
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All my wife's driving is journeys of under 2 miles. ALL. She averages 49mpg in her diesel Peugeot 106 - a little less in winter , a little more in summer.
If the car was petrol engined, it would be 10mpg less and the car would be dead....
Edited by madf on 03/05/2009 at 20:42
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Broadly same experience as Robin and Humph.
Car part of my commute is 5 miles to the station at 06:30; always from cold. In a 1.6 petrol BX I was lucky to get 30mpg, changing to the 1.9 D (no turbo) sent it straight to the low forties.
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Which way? :-)
well we do similar miles in a 7 day period.
We both use the same car for work commuting and I use it in the week and the missis at the weekend.
So we are both trying to achieve the most mileage for the least diesel used.
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My diesel VW has an electric ceramic heater in in the heater matrix box and heated seats. This the best of many worlds. I would never go back to petrol unless the price difference got a lot larger or there was some new gasoline invention that made it more attractive.
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My diesel VW has an electric ceramic heater in in the heater matrix box
I had a Mercedes A Class courtesy car with (I presume) ceramic heater and it really was amazing - warm air pretty well instantly. Why on earth don't all cars have those?
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I've noticed this to be quite significant in my Passat TDI. It takes about 10 minutes to reach normal temperature on the gauge, but closer to 30 minutes before it starts to produce it's best MPG. It can do more than 60 mpg when perfectly warm and doing 60 mph, but until it's warm it drinks fuel.
This is especially noticeable at higher speeds, when it can be up to 10 mpg difference.
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>> My diesel VW has an electric ceramic heater in in the heater matrix box I had a Mercedes A Class courtesy car with (I presume) ceramic heater and it really was amazing - warm air pretty well instantly. Why on earth don't all cars have those?
My Mk4 Mondeo has one, listed on the Ford ETIS specification sheet as "auxilliary air heater", warm air from the heater vents within 60 seconds.
Edited by kith on 04/05/2009 at 23:52
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Saab 2.2TID (the one with the tractor engine). Needs 4-5 miles to get temperature gauge off zero, but really doesn't get into its stride for 15 miles plus, then 42 mpg long-term average
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Because it's cheating! The warmth will be so much more appreciated if you have to wait for it.
I had a Mercedes A Class courtesy car with (I presume) ceramic heater and it
really was amazing - warm air pretty well instantly. Why on earth don't all cars
have those?
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My Bentley had an electric blow heater I think. Instant functioning.
The other thing about that car, superb in many ways, was that it stayed warm inside when parked in cold weather for twice as long as any other car I have had. Something to do with weighing 50,000 tons and doing 8 mpg round town I guess.
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