SOT: MPG and differential

Tread depth will vary it far more.

I've not tried it when I've let the engine speed drop really low. I'm not sure how slowly I'd have to go in 6th gear for the engine speed to be below normal idling speed.

Agreed. Constant fuel consumption in litres/minute but variable speed and therefore distance travelled in that minute. I've done it at somewhere between 40 and 60 (out of a built-up area on an open road with fewer hazards).

Tread depth will vary between about 1.6 and 6 mm (legal limit and brand new) as a proportion of a tyre which is around 600 mm diameter so 300 mm radius (approx).

So difference of 4.5 / 300 = 1.5%

Unless I've got my estimate for max tread depth when new and total tyre diameter hopeless wrong.

There are two or three issues. Firstly the car may be a plugin., which gets extra energy from the mains Secondly it is possible to use a smaller engine that operates closer to best efficiency thirdly it gets energy back from the 'brakes'...

You might get 1/4" on a 24" diameter tyre. ~1% On larger diameter wheels, even less...percent wise

All the ones I have used are spot on with the GPS when I am directly approaching them

No.

There was of course a float valve so the fuel pump did not 'pump fuel into the cylinders'

The carburettor however would suck some fuel in, but normally the engine would just pump it out again. Surprised you managed to flood it

BTW the correct way to do this is to switch off the engine and then press the throttle fully down. The air pumping then is a better brake.

But not only was

I don't know quite how much they vary, but making an assumption that those signs represent a gold standard for speed measurement seems illfounded.

I think they can only be cheaper* to run if they are charged at home and used mostly for journeys within their battery range.

Your argument seems to be more related to self-charging hybrids than plug-in hybrids?

In the days when I was taking the kids 250 miles to University, the speedo cable broke the evening before one trip and I had no time to replace it.

A good friend lent me his hand-held GPS, which had the useful feature of a full-screen speedometer. I blu-tacked that to the windscreen just above the line of sight for the non-functioning speedo, loaded the car, and set off, driving at 70 (it was almost all motorway). To my surprise we got to Uni about half-an-hour earlier than normal. Ditto on the return journey.

When I’d replaced the broken cable, I checked the two against each other, and the speedo was reading 10% high…After that I drove at around 77 in a NSL…it felt odd at first…

Update. The car has gone to the garage today for the air conditioning condenser to be replaced. He will also check the compressor as part of the recommissioning of the aircon.

I mentioned the other problems. He will check the fan and the oil for the differential (which is the same oil as the gearbox). Out of interest, I asked how this is done and he said it is a sophisticated technique involving removing a bung and sticking a finger through the hole. Is this SOP?

Very often. In the old rear wheel drive days, the differential had an oil filler partway up the casing, and the correct level of oil was at the bottom edge of the filler hole i.e. put oil in until you can't fit any more in.

Same as my Citroen Berlingo.

I read somewhere that as a rule of thumb, if you pay more than 45p/kWh, petrol's cheaper.

Same as the reduction gearbox on various Hyundai/Kia EVs...

Some modern stuff may not have a drain plug, in which case you have to suction out the oil via the filler hole with a pump or syringe.

Theo

Even if you don't ever plug them in, they still benefit from increased efficiency in the same way as any other hybrid, you're just not making good use of the bigger battery.

(There is a huge range of different arrangements all called "hybrid" of one sort or another; what I said is based on my experience of a Renault PHEV).

nib

Is this just to check how much oil is there, or can he assess the quality of the oil by looking at his finger, colour perhaps?

Indeed. But they are what is used (the same technology) to give you a speeding ticket, and it is not hard to make doppler radar amazingly accurate.

delta(f) = 2 * v / λ is the frequency shift equation

v is - say 40km/h and 1/λ is the radar frequency - 35GHZ as a representative example - divided by the speed of light.

so DF = (2 x 40 / 3 x 10^11)* 0.35 x 10^11 - knock out the 10^11 terms

DF = 80 * 0.35 /3 or somewhere ion the 8-10Hz region. Not exactly hard to measure to 1% or better.

But the fact is that I use GPS on my satnav which gives me exact speed and its always corresponded exactly with the radar signs, but never with the speedometer

On a long journey, the plugin bit will be all used up pretty soon

On a short trip it will ensure infinite fuel efficiency as the motor never gets started at all.