Re: OT - Diesel engines

On 4 Sep, 18:36, "Mortimer" <m...@xxxxxxxxxxx> wrote:
"guy" <guyswetten...@xxxxxxxxxxxxxx> wrote in message

news:1188893970.325476.145680@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx

Last year I made about 20 trips from Edinburgh to home by car .19
Octavia PD diesel 136hp = so nothing special. every trip took 3hrs
10mins +-10secs, same driving conditions, traffic etc every trip.
However, when the outside temperature was 24C I got about 63-63 MPG
(trip computer), when it was 15C I got about 56-57MPG. obviously there
is the fuel cost in keeping the engine hot but this seems a big
difference.

I'm intrigued by the observation that all the 3-hour journeys took the same
time +/- 10 seconds. I'd have expected a much greater variation: it only
requires one adverse traffic light or a sequence of a couple of cars on a
roundabout and you've added more than 10 seconds.

I'd have expected that the economy would have been better when the
temperature was cooler:

- no air conditioning on

- air is denser therefore you may get more air in the cylinder and
consequently better combustion without unburnt fuel

- if the radiator fan is intermittent, it will be on for less time in colder
weather, especially if some of the heat is diverted into the heater

Was the lighting the same? Could you have had the lights on during the
colder weather when it may have got dark earlier?

Either way, your car's better than mine: my Peugeot 306 2.0 HDi does about
52 in non-urban traffic (single carriageway or motorway: 50-70 mph). I've
not noticed consumption vary according to temperature, but then I can only
base my consumption figures on tank fillings because I don't have a trip
computer.

Yes identical times every trip from 4pm to 7pm ish. No lights
required.
Minor use of wipers on 1 or 2 trips.
6 speed manual box
15 miles or so of motorway maybe 4 of dual carriageway, the rest
single carriageway so lots of cruising at 60 with a bit of 40mph stuck
behind ferry traffic and some hard accelerating to get past the ferry
lorries.

The best economy I have had was 18 miles to the supermarket and 18
miles back on a really hot day. 72mpg! (and I was driving normally)
It is noticable that in summer I regularly get 60+ mpg but rarely in
winter.

Guy

.

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