From Wiki: Brake fade - Wikipedia
Causes of brake fade
The reduction of friction termed brake fade is caused when the temperature reaches the “kneepoint” on the temperature-friction curve. [All brake lining is cured under mechanical pressure following a heating & cooling curve, heating the friction material up to 450°F to “cure” (cross-link) the phenolic resin thermoset polymers: There is no melting of the binding resins, because phenolic resins are thermoset, not thermoplastic] In this form of fade, the brake pedal feels firm but there is reduced stopping ability. Fade can also be caused by the brake fluid boiling, with attendant release of compressible gases. In this type of fade, the brake pedal feels “spongy”. This condition is worsened when there are contaminants in the fluid, such as water, which most types of brake fluids are prone to absorbing to varying degrees. For this reason brake fluid replacement is standard maintenance.
Seems we’re talking about two slightly different things in this thread:
-Coasting down a hill in neutral vs driving down a hill under power (at the same sort of speed you might achieve coasting)
-Engine braking vs friction braking
I can coax my miles-per-tank up to 350 or so if I take advantage of all the hills around here. Normal miles per tank only goes up to 320 or so.
I speed up to 60 or so, slip into Neutral, and coast down the hill. The hills aren’t steep enough that I need to brake, and it’s obvious to me that I can coast longer in Neutral than while in gear. I only do this if I can coast for 60 seconds or so. Coming home to my old house at a lakeside community, I could coast for a good 2 miles.
[QUOTE=Critical1]
if they brakes fail due to overheating there is no reason to think the emergency brake would also fail…
[/quote]
Sure there is, as has been explained elsewhere in this thread. If the car has rear disc brakes and the E-brake uses those pads, those pads will already be overheated and have little or no stopping power. If the car has rear drum brakes, the drums will expand to where the shoes don’t contact them. If the car has rear disc brakes with a separate drum parking brake, those tiny parking brake shoes - which are hardly up to stopping the car under good conditions - would overheat in short order.
But as has been previously mentioned, it’s not only boiling brake fluid that causes overheated brakes to fail.
That is true.
A.R. Crane has supplied one cite. I have an article from an automotive trade journal that explains how brake pads only work effectively within a certain temperature range, but it’s on paper so I can’t show it to you. I have personally experienced brake drum expansion resulting in no braking from the rear. Do some research and I’m sure you’ll find the evidence you want. But do yourself a favor and don’t think that just because it hasn’t been proven to you yet that it isn’t true.
With reference to the OP
[QUOTE=EmAnJ]
For some reason I seem to think that it’s illegal to coast in neutral down a hill, in either a manual or automatic transmission. This may be a Canadian provincial or federal law, or it may be bullocks. However, now I’m wondering why it would be illegal? I would suppose this kind of law would somehow be based on potential danger, but what danger?
Anyone have any insight?
[/QUOTE]
Not covered in the Ontario Highway Traffic Act, and I doubt that it would fall under Federal jurisdiction in any way. I didn’t check other provinces - where are you located?
[QUOTE=Zerc]
I think that if you want to improve your economy on a downhill you should not put in your clutch but rather just take your foot off the accelerator. The reason for this is if the clutch is in you still need to use fuel to keep the engine turning but if the clutch is out then then tyre rotation will keep the engine turning and no fuel will be used. It works like this on my car and saves me about 0.1 litres/100km 
(When I say the clutch is in I mean that the pedal is depressed)
[/QUOTE]
Zerc,
The Scangauge meter I have attached to my '02 Sable indicates 0.4 Gallons Per Hour being consumed even on a steep downhill.
Is that a spurious reading caused by the fact that the system is measuring airflow rather than directly metering fuel?
Never mind. My question was answered.
AFAIK, modern fuel injected vehicles will generally shut off fuel flow when the there is no pressure on the gas pedal. However, the injectors will turn back on to maintain a minimum idle speed. So, if you are going downhill in neutral the injectors will be on to keep the engine at idle speed. However, if you are in gear and allowing the engine to turn over at, say, 1500 rpm, the injectors will be off. As a result, you use more gas in neutral.
Using the engine to slow the vehicle does indeed cause slightly more wear to the drivetrain than if the brakes are being used. Although the wear is not severe, IMO it’s better to use the brakes: this way, the wear is limited to one cheap and easy to repair area. But I grant you, on modern roads the issue is usually moot. Even on very long downgrades, where one is forced to use the brakes periodically to keep the speed down, the brake applications are far enough apart in time such that brake overheating is unlikely.