Improving fuel economy of bigger and smaller vehicles

[octo0072000]

Dodge Challenger 8spd auto claims more mpg than the 6 spd manual - the auto has a facility to shut off four cylinder on constant low throttle - activates them instantly when you deck it - I couldn't tell when it was operating, although others claim to.
Although the system is blamed for premature cam follower failure and associated cam lobe being destroyed rather earlier than you might expect, slightly negating the money saving of an extra mpg or several.

I bought the manual as it is rated something 5bhp more Sat in the station car park the other day, engine running, waiting for her train to arrive and deliver her home, I noticed the mpg display ticking down 0.1mpg fairly regularly . . .

didn't the old Chrysler 300s have that system of dropping cylinders on overrun

 

[Bornfree]

didn't the old Chrysler 300s have that system of dropping cylinders on overrun

My cortina used to do that. But mainly under acceleration.

 

[stuvy]

Dodge Challenger 8spd auto claims more mpg than the 6 spd manual - the auto has a facility to shut off four cylinder on constant low throttle - activates them instantly when you deck it - I couldn't tell when it was operating, although others claim to.
Although the system is blamed for premature cam follower failure and associated cam lobe being destroyed rather earlier than you might expect, slightly negating the money saving of an extra mpg or several.

I bought the manual as it is rated something 5bhp more Sat in the station car park the other day, engine running, waiting for her train to arrive and deliver her home, I noticed the mpg display ticking down 0.1mpg fairly regularly . . .

They have been doing that for years on the HEMI v8 not the first manufacturer but the. Wonder why the engines are pigs to tune

 

[bricol]

didn't the old Chrysler 300s have that system of dropping cylinders on overrun

Same drivetrain. Same issues. But when running and driving - 70mph down the freeway at less than 2000rpm on four cylinders.

 

[bricol]

They have been doing that for years on the HEMI v8 not the first manufacturer but the. Wonder why the engines are pigs to tune

Leave it standard and its fine. 2016, which mine is, are and onward, are locked - computer needs sending off to be unlocked, or swopping for an unlocked one. But then if it doesn't like talking to all the other modules in the car, you're stuffed! Even changing the radio touchscreen can bugger everything up - lose access to the setups for different modes etc.

It would be a lot better with simply knobs and dials for heating, tuning, etc - I have to wear a pair of bifocal spectacles - main lenses to see down the road, the secondary to see the flippin' screen so I can demist the windscreen . . .

I was amused to discover you can buy aftermarket camshafts specifically to "lope" . . . make it sound old-school uneven idle as though it had a hot cam, even though they don't do anything for power output.

When I added up the cost of the required additions to make it run with only a cam change, I decided standard power would be good enough, seeing as its close to double anything else I have

 

[redlig]

Chatting to a guy yesterday who recons that when he ran his Skoda down to 45 miles left in the tank and running gently he got a message on his dash stating" 2 cylinders " They think of everything.

 

[Morrisman]

But when running and driving - 70mph down the freeway at less than 2000rpm on four cylinders.

My Mondeo does that, 70mph at 2000rpm. Mind you, it 'red lines' at 4500.

 

[Edward Teach]

Bigger wheels could actually make MPG worse due to the higher gearing making the engine struggle.

I had this on an Astra J ecoflex I had.
Fitted wheels with a 3% larger rolling circ.
Measured MPG dropped about 10%.
On the car I had I think it was already geared very highly & the slightly bigger tyres took it over the top.

Fitting larger diameter wheels will change the speedo accuracy, so your mpg will differ.

 

[james butler]

something that has crossed my mind with modern diesels is the need to keep well over 100bhp cool, this in turn is completly useless and not needed when using 25bhp to do 70mph down the motorway.
this specifically effects the intercooler! my old 1.9sdi golf regularly did 55-60mpg, it was phenomenal but was i think 75bhp and had no intercooler
my 1,6 connect does 50, wheres the other 15mpg? im convinced that overcooling of some components like the intercoolers on modern cars actually reduce their efficiency and maybe why companies are even fitting smart grills that only open when needed ie really hot.
so maybe on the average joe motor hypermiling you could get a pizza box wedged over the grill to reduce overcooling and increase mpg? after all diesels like heat

 

[Gareth J]

something that has crossed my mind with modern diesels is the need to keep well over 100bhp cool, this in turn is completly useless and not needed when using 25bhp to do 70mph down the motorway.
this specifically effects the intercooler! my old 1.9sdi golf regularly did 55-60mpg, it was phenomenal but was i think 75bhp and had no intercooler
my 1,6 connect does 50, wheres the other 15mpg? im convinced that overcooling of some components like the intercoolers on modern cars actually reduce their efficiency and maybe why companies are even fitting smart grills that only open when needed ie really hot.
so maybe on the average joe motor hypermiling you could get a pizza box wedged over the grill to reduce overcooling and increase mpg? after all diesels like heat

Your "missing" mpgs have gone into lots of things; egr (to keep combustion temperatures lower and reduce NOx at the cost of efficiency), more restrictive post combustion devices, catalysts, DPFs; maps that minimise NOx. All of which make the exhaust more palatable but cost fuel efficiency.

Over cooling of diesels is really important too. Manufacturers do lots of stuff to try to get diesels up to temp quickly and keep them there at low loads; egr "cooler" which could be thought of as coolant preheater, rad flaps, egr itself, electric preheaters that add load to the alternator (increasing engine load) and dump this load into the coolant, webasto type preheaters, engine insulatoin etc, etc.

One of the reasons why I suggested a coolant preheater as a useful mpg increaser. I have one, it helps.

I rewrote the code for my temp dial to make it more sensitive, I used to commute into town which was on average downhill. Some days, the needle would only get part way and you could watch it drop slowly on a long downhill bit. Incidentally, at this time I admit to experimenting with terrible and dangerous practice of coasting that is pointless in real world driving. Employing coasting the needle didn't get off the stop, actively "driving" up the hills, the needle would get to helf temp.

(I should mention that, I was pretty meticulous with servicing, replaced the thermostat and checked it's operation via obd. The cooling system worked fine on a longer trip)

 

[Olderisbetter]

Fitting larger diameter wheels will change the speedo accuracy, so your mpg will differ.

I.have a gps speedo as it is an import in km/h but i see your point

 

[arther dailey]

I used to hang one of those parafin green house heaters on my truck bottom hose in winter , kept it frost free, engine was virtually instantly warm, no warm up period ,lower overall fuels costs ,warm cab, win win.

 

[james butler]

Your "missing" mpgs have gone into lots of things; egr (to keep combustion temperatures lower and reduce NOx at the cost of efficiency), more restrictive post combustion devices, catalysts, DPFs; maps that minimise NOx. All of which make the exhaust more palatable but cost fuel efficiency.

Over cooling of diesels is really important too. Manufacturers do lots of stuff to try to get diesels up to temp quickly and keep them there at low loads; egr "cooler" which could be thought of as coolant preheater, rad flaps, egr itself, electric preheaters that add load to the alternator (increasing engine load) and dump this load into the coolant, webasto type preheaters, engine insulatoin etc, etc.

One of the reasons why I suggested a coolant preheater as a useful mpg increaser. I have one, it helps.

I rewrote the code for my temp dial to make it more sensitive, I used to commute into town which was on average downhill. Some days, the needle would only get part way and you could watch it drop slowly on a long downhill bit. Incidentally, at this time I admit to experimenting with terrible and dangerous practice of coasting that is pointless in real world driving. Employing coasting the needle didn't get off the stop, actively "driving" up the hills, the needle would get to helf temp.

(I should mention that, I was pretty meticulous with servicing, replaced the thermostat and checked it's operation via obd. The cooling system worked fine on a longer trip)

true true
i have noticed it takes a lot longer in winter to get up to temp and maintain it.
only reason i mention it was someone mentioned driving hard up to speed and then taking it easy at cruise speed works wonders for mpg making sense to me that heating up quicker is part of the issue and like you say yourself a coolant preheater helping getting up to temp quicker.
ive also noticed on roadtrips after driving for 3/4 of an hour only then does decent mpg occur again making sense to me that it takes that long for absolutely everything to get to temp and do what its supposed to.
was only a suggestion after seeing so many black cabs doing it

 

[DAPPH]

I.have a gps speedo as it is an import in km/h but i see your point

On the fishing site I play on a guy called Mike Thrussel was driving up the A 74 (? ) in Scotland when his speedo died ( so he say's ) his satnav said he was doing exactly 58 MPH as he passed a working GATSCO speed camera .......it flashed . He was ticketed with a clocked speed of 66 MPH IIRC.
He hadn't realised when using a sat nav that the undulations of a road on a hilly measured mile will show a shorter distance & thus calculate a lower speed as the satellites will be measuring a straight line between points They don't usually show the ups & downs of the road surface like a measured mile check does.

 

[DAPPH]

true true
i have noticed it takes a lot longer in winter to get up to temp and maintain it.
only reason i mention it was someone mentioned driving hard up to speed and then taking it easy at cruise speed works wonders for mpg making sense to me that heating up quicker is part of the issue and like you say yourself a coolant preheater helping getting up to temp quicker.
ive also noticed on roadtrips after driving for 3/4 of an hour only then does decent mpg occur again making sense to me that it takes that long for absolutely everything to get to temp and do what its supposed to.
was only a suggestion after seeing so many black cabs doing it

It depends of the chill factor of the incoming air through the rad and around the engine the faster you go in cold air the more chilling effect it has. The thermostat reduces the hot coolant flow away from the engine till it is hot enough to open more an release excess heat . It's a fine line on where the advantage / break even point is . IIRC you used to be able to get summer & winter bellow thermostats to help with thefuel economy on the bigger trucks & plant machinery

Having a variable speed & temperature cold air stream on a truck in a tunnel connected to a decent dynamometer rig would give you the results ..some of which might really surprise you

 

[bricol]

Intercooler cools the compressed air after the turbo - cooler air is denser, so a given volume contains more oxygen and therefore your engine develops more efficient power.
In most situations a road car intercooler is really a heatsink - you deck it, boost goes up, load of hot air passes through the intercooler/heat-sink and is cooled down - the intercooler/heat-sink gets a bit warmer - but now you've slowed down as you've reached the speed you want/slower car infront/red light . . . so the air cools the intercooler/heatsink ready for the next bit of boosted progress.

 

[Munkul]

Yes it is.
They are a lot closer now. 4mpg doesn't sound a lot but it soon adds up if you do big mileages.
I suppose type of route also makes a difference.
Mine tends to be a mix of motorway / dual carriageway and twisty country roads. Perhaps constant city driving would favour an auto more?

The newer 8spd+ autos are usually more efficient than the manual equivalents.
I only know this because I've had several...

 

[fizzy]

The newer 8spd+ autos are usually more efficient than the manual equivalents.
I only know this because I've had several...

So have I. But have you had identical cars one manual and one auto everything else the same? Because I hire cars constantly I go through more cars than most so often have identical models with small changes.
I do drive very hard. I get 36mpg out of a car that most people would return 50mpg. So perhaps it is my driving style but I do still see a difference between auto and manual but the gap has narrowed.

 

[Justme]

On the fishing site I play on a guy called Mike Thrussel was driving up the A 74 (? ) in Scotland when his speedo died ( so he say's ) his satnav said he was doing exactly 58 MPH as he passed a working GATSCO speed camera .......it flashed . He was ticketed with a clocked speed of 66 MPH IIRC.
He hadn't realised when using a sat nav that the undulations of a road on a hilly measured mile will show a shorter distance & thus calculate a lower speed as the satellites will be measuring a straight line between points They don't usually show the ups & downs of the road surface like a measured mile check does.

He would have needed to be going up / down a 14% (about 1in 4) gradient at the time.

More likely it lagged due to a bad signal & caught up just after the flash.

 

[Justme]

So have I. But have you had identical cars one manual and one auto everything else the same? Because I hire cars constantly I go through more cars than most so often have identical models with small changes.
I do drive very hard. I get 36mpg out of a car that most people would return 50mpg. So perhaps it is my driving style but I do still see a difference between auto and manual but the gap has narrowed.

The mpg difference prob says more about how you drive the auto than the auto itself.

I would hazard a guess that you rev it up a fair bit to get it moving as your not getting the instant movement you would normally get with a manual as you add gas.

Lots of auto drivers over gas to get the car moving.