Fuel Misers

[gbb]

My old man had this year's ago with a Citroën ZX he bought a new one & it was great, 3 years later bought another which just did not perform anywhere near the one before. Slower, didn't pull the caravan as well, worse economy, took it back several times but they wouldn't have it, it was within specification as far as they wereally concerned. He got rid of it after 18 months & boycotted Citroën for 10 years.

It could be the same scenario as mine. Same engine but now more stringent emissions to meet, coupled with extra weight. Because of the extra weight, the emmissions are almost exactly the same as the former model.
I perhaps foolishly rejected the idea of a 1.4 turbo model for the same price...it may have been a better option...but i have this aversion to the idea of a small engine in a big car.

 

[Drago]

Potentially small engines are more robust - less forces exerted on lighter reciprocating masses. Ancillary bits like turbos may potentially have shorter lifespans, but the engines themselves are less likely to burst.

 

[Deleted member 26715]

Potentially small engines are more robust - less forces exerted on lighter reciprocating masses. Ancillary bits like turbos may potentially have shorter lifespans, but the engines themselves are less likely to burst.

I'd refute that claim on the grounds that it would be about the state of tune, a highly tuned 1.2 to get the same hp as standard 1.6 will have to work harder & therfore more likely to failure.

 

[Dirk]

I still place something in front of the radiator to prevent the cold winter blast excessively cooling the engine, done that for donkeys years, allows the engine to reach temp sooner as well.

No point in doing that if there is a thermostat in the system and it's working properly.

 

[Dirk]

I'd refute that claim on the grounds that it would be about the state of tune, a highly tuned 1.2 to get the same hp as standard 1.6 will have to work harder & therfore more likely to failure.

Not necessarily. It depends how well designed the engine is, quality of engineering and materials used.

 

[gbb]

No point in doing that if there is a thermostat in the system and it's working properly.

Good point, im probably still stuck with an old scenario in my past where a a car struggled to get up to temperature and allow good interior heating, blanking did help that. I'l concede it probably has no p,ace in a properly working modern car.

 

[Drago]

I'd refute that claim on the grounds that it would be about the state of tune, a highly tuned 1.2 to get the same hp as standard 1.6 will have to work harder & therefore more likely to failure.

Which component works 'harder'? Please explain.

I've already explained, smaller pistons endure less inertial forces for a given RPM (in effect, at the end of each stroke the 'weigh' less, so place less strain on themselves, rods, cranks and supporting cases), so it's the pistons and moving parts in the larger engine that are having the harder time.

As I mentioned in my previous post, it's ancillary items such as turbos that tend to suffer, not the actual engine. The basic engine itself, like for like, is actually less likely to suffer a catastrophic failure for the reasons I've just cited. If you know of a mechanism that dictates otherwise then please enlighten us with the actual technical details rather than vague notions of working 'harder'. Equally, if you know of some obscure branch of physics that makes heavier items endure less inertial forces than light ones, then again feel free to enlighten us.

This idea that larger engines are inherently more reliable or longer lasting than engines of similar output but smaller swept volume is urban myth. There is no physical reason for this to be so.

 

[Dirk]

I've already explained, smaller pistons endure less inertial forces for a given RPM (in effect, at the end of each stroke the 'weigh' less, so place less strain on themselves, rods, cranks and supporting cases), so it's the pistons and moving parts in the larger engine that are having the harder time.

That depends on the piston speed of the engine.
At a given RPM a short stroke motor has a slower piston speed than a long stroke one and therefore less inertia for the same engine capacity. ie. a small capacity long stroke motor could generate more force than a large capacity short stroke one.

 

[Mr Celine]

In October we replaced our big car with a nine month old 7000 mile Seat Leon FSR 2 litre diesel. This is supposed to have similar combined mpg to its predecessor, a Golf 1.6 diesel estate, which was 63 mpg.
On playing with the Leon's trip computer I found that it had recorded average mpg from new as only 39 mpg.
By the time I'd driven it the 50 miles home it was already over 40 and was pushing 50 when it reset itself at 8000 miles. Currenly averaging 58 mpg between fill ups which isn't bad for winter and I haven't really been trying economy wise.

 

[Drago]

That depends on the piston speed of the engine.
At a given RPM a short stroke motor has a slower piston speed than a long stroke one and therefore less inertia for the same engine capacity. ie. a small capacity long stroke motor could generate more force than a large capacity short stroke one.

Absolutely! And long stroke motors tend to be those of a larger capacity, to give more time with each revolution for the combustion process to complete.

There are many, many, variables, but all other things being equal there is no reason in either physics or engineering why a 1.4 litre turbo of 100 HP should be any less durable than a 2 litre NA engine of 100 HP.

 

[swansonj]

A few of you upthread questioned my assertion that slowing down uphill was more effective at saving fuel than slowing down on the flat. Apologies for the delay in responding, I was waiting for an appropriate motorway journey to check the consumption figures.

It’s actually difficult, because the mpg is so sensitive to gentle gradients, you can never be sure when you are on dead flat road. But my best estimate is:

Flat road

60 mph (my normal speed, chosen as my personal compromise between mph and mpg): 70 mpg

Maximum efficiency: at about 45 mph, 90 mpg

Going up one of the steeper hills that you find on motorways:

Maintaining 60 mph: 30 mpg

Dropping to 40 mph: 45 mpg

So, for 1 mile up that hill, dropping speed from 60 mph to 40 mph saves (1/30 – 1/45)=1/90 gallon. It adds (1/40-1/60) hours or 30 seconds. For that same time penalty on the flat, I could do 1.5 miles at 45 mph instead of 60 mph. That would save 1.5x(1/90-1/70) = 1/210 gallons.

So dropping the speed on an uphill saves more fuel than dropping the speed on the flat (in this particular example, more than twice as much).

This is on a small, light, underpowered (by conventional standards) car (Citigo 1 litre eco). I have said previously that driving an underpowered car makes the effect of accelerator use, hills, winds etc more obvious than driving a heavier but higher-powered car, where everything seems to get “smeared out” more. But I believe that the same principles apply to any car (although the optimum speed for any given gradient would be different).

 

[gbb]

In October we replaced our big car with a nine month old 7000 mile Seat Leon FSR 2 litre diesel. This is supposed to have similar combined mpg to its predecessor, a Golf 1.6 diesel estate, which was 63 mpg.
On playing with the Leon's trip computer I found that it had recorded average mpg from new as only 39 mpg.
By the time I'd driven it the 50 miles home it was already over 40 and was pushing 50 when it reset itself at 8000 miles. Currenly averaging 58 mpg between fill ups which isn't bad for winter and I haven't really been trying economy wise.

This kinda echoes my experience with my sons Vectra turbo diesel SRI he had. He was averaging less than my 1.6 petrol astra, despite his car being potentially far more economical. I had no problem boosting his mpg figure'. ..not that he cared.

 

[Drago]

People by diseasels for the economy, and then cane them everywhere, utterly destroying any small advantage of owning one. Why?

 

[Dirk]

People by diseasels for the economy, and then cane them everywhere, utterly destroying any small advantage of owning one. Why?

I don't.
I bought one for the economy and drive accordingly.
I also bought one for the higher torque of a diesel engine, which makes towing a caravan easier.

 

[Drago]

Right, just given the Pension Book Special a clean.

I got a hossy appointment at half nine tomorrow, so I've plugged in the pre heater and set the time. Should use less fuel when pre warmed, and the immediate presence of warm air when the engine starts will be a billy bonus.