Driving in neutral (i.e., coasting) is illegal almost everywhere in the U.S. and probably Europe. The theory is that if the engine is needed in some emergency situation, one must first engage the transmission which is a time consuming one-step or two-step process — and the driver may accidentally engage the wrong gear. There is some who say that this process causes undue wear on the transmission and/or clutch system. Also, this encourages speeding (acquiring enough momentum to make it part of the way up the next hill.)

Each engine design has a different peak r.p.m. efficiency curve. There is no standard.

Using the cruise control is illegal in many urban areas. In any event, cruise controls are not designed for fuel efficiency. They are designed to acquire and maintain a certain designated speed. Thus, they waste fuel in effort to acquire the speed in that they accelerate faster than one would do if one does not worry how soon the 50 or 55 mph will be acquired.

Finally, parking so that one does not have to back out saves fuel — that’s a good idea. And it’s particularly handy if one just robbed the bank.

35 psi is not the manufacturer’s spec for our car, it’s 39 front 37 back when minimally loaded and 42 and 41 for fully laden.

As to revs there cannot be a standard value that is optimal, all engines are different and will have different efficiencies at different rpm.

35psi is manufacture specs.

Didn’t understand your engine rev statement.

enjoy.

Many thanks for the additional tips. However, isn’t coasting in neutral on the public highway actually illegal. There is an argument in law (and, yes, the law is an ass) that the driver has less control over the vehicle in neutral.

Also, I was driving yesterday and thinking about the engine revs issue. Surely, it’s totally different depending on the size and weight of the vehicle, the power of the engine and the specific efficiencies of the transmission. Indeed, a petrol engine on a big heavy, old car might be labouring at a certain low rev count but amble along optimally at higher, whereas a diesel is quite happy to run at lower revs with no loss of efficiency. I think the key is to not have the engine screaming at too high a rev count and not to have it grumbling at too low. The sweet spot is probably very different for different vehicles.

Yesterday, I was getting 51 mpg averaged over 300 metre sections of road in our small diesel at around 2000 rpm, nothing I did, other than breaking, seemed to change that. In fact, breaking seemed to nudge up the average slightly, but I guess that the stopped car was using less than if I were moving.

The same goes for tires. 35 psi is nowhere near the recommended pressure for our fully laden Ford MPV with all seven seats occupied and luggage in the back.

When approaching a stop light, put car in neutral and coast to a stop. No load on engine, means saving gas. If you drive up a hill or over a bridge, put car in neutral on the down side and coast, engage cruise control to continue.
By all means, use your cruise control and set it for 50 mph or below. This will add 5-10 mpg’s. 1500 rpm is the sweet spot, try to stay near it.
If you use ethanol, 1/4 of your tank can be filled with water! Good idea about running on 1/2 tank.
Engage your cruise control when you reach 25 mph and let it do the shifting
up to 50 mph, much better than your foot on gas petal.
I brought a Yamaha Zuma and it gets 125 mpg! I use it for short hops
to the postal office or store and leave my monster Jeep Commander at home;
although, it has a variable displacement engine that runs on 4 cylinders when cruise control is turned on. But, do buy a cheap scooter for short trips or just cooling off on a hot summers day.

When you take off from a stop light at reach 25 mph, resume cruise control again. If you had it previously set for 50 mph, it should engage and accelerate
you up to that speed again, much better than a heavy foot will do. What I meant to say. Always pull into a space to park, that you don’t have to back
out of, waste gas. If possible, park on the downhill side and coast when taking off. I think a few extra PSI on your front tires, will make them easier to turn
and more efficient, less friction. But back tires should be at norm, 35psi.

Enjoy your motoring and respect others.

Cheers;
dr burke.
USA