Just a question about what temperatures give the best MPG... I am in Phoenix and haven't seen anything below 40 in the two weeks I've been driving a certified '04 and I'm sustaining between 45 and 49 mpg despite two > 1 mile trips a day. That said, I'm wondering if I'll see a boost in fuel economy when summer hits (in late February). Do temperatures in the 90's, 100's or 110's continue to positively effect FE? Also, I haven't messed with the tire pressure yet but with the temperatures getting as high as they do here, is that something I need to be particularly careful with?
In hot weather like in Phoenix, you have to run the AC. Running the AC takes energy. Energy comes from gas - yes, in the Prius - it all comes from gas. If you use the AC more, you end up using more gas. Batteries also discharge faster and don't take as much charge when they're hot. So, extreme temperatures on either end will affect your mileage. The benefit in hotter weather is that the engine doesn't take long to warm up. The detraction is that it has to use it's cooling system more. I'd say ideal conditions are somewhere around 70 degrees, drives of no less than 10 miles or so on long straight level roads with a speed limit around 50mph.
Your best mileage will be at the highest ambient temperature where you don't need to run the climate control system to cool the interior. Also it will occur at speeds of 35 to about 45 MPH, on flat ground. Finally, DO keep your tire pressure at correct levels. It's important no matter where you live. I use 40 PSI front and 38 PSI rear. Some use even higher pressures. Up to the max. inflation pressure (listed on tire sidewall) more pressure is good, other than for ride smoothness. Most modern tires will not wear the centre faster than the sides unless you get very silly with pressure. If you run lower pressures, you can overheat the tires. You will also get poorer traction in rain and snow. So keep the tires at least as high as the door placard indicates, or higher, up to the max. pressure imprinted on the tire sidewall ("maximum load xxxx lbs at xx PSI"). This isn't the max. pressure the tire can stand, but it indicates the maximum load the tire is rated for, and as tire pressure is the controller for this, the pressure this warning indicates is the maximum -usable- pressure the tire was designed for.
Yep, in Phoenix, you will have those one or two weeks each year where the car warms up quickly, but it isn't so hot that you need to run the AC. You should get great mileage then. :madgrin: In Sacramento, I get the best mileage in Oct. before it gets too cold.
My guess? 20°C/68°F. It's warm enough for short engine warm up times but not hot enough to run the A/C or have the windows open.
how much does having the windows affect FE? anyone got percentages on this? better to roll down windows or turn on the A/C?
I've done a little testing of this. With my limited testing and the measurements and reports of others, I would say at speeds above 35 MPH (70 km/h) it's more efficient to have the A/C running. The difference is small enough that it -can- be swamped by other factors, but you can actually see the car being held on a downhill by the aero forces when you open the windows. That is, with windows closed the car will coast up to a much greater speed than with the windows open.
I think this answer will be speed based. At high speeds it is better to run the AC and roll your windows up. At low speeds AC off and windows down. This sounds logical anyway. I think the most important factor is keeping your battery and inverter cool. It seems more failures happen in very hot regions.
Well i know about engine block heaters for cold places... there anything that can be done for our cars in hot weather in a preventive fashion?
The usual, simple things like parking in the shade, and leaving the windows open a bit. I don't know of any block coolers.
I tinted the windows to the legal limit in my state, and park facing north, so the untinted windshield lets in the least heat. In Arizona, Non-reflective tint is allowed along the top of the windshield above the manufacturer's AS-1 line. Front Side Windows Must allow more than 33% of light in. Back Side Windows Any darkness can be used. Rear Window Any darkness can be used. Front Side Windows Must not be more than 35% reflective. Back Side Windows Must not be more than 35% reflective. The tint color(s) of RED AMBER are not legal by state law. Dual side mirrors are required if back window is tinted.
Actually, you want the ICE warm as soon as possible. The issue in the summer is cooling the humans and the battery. You could just arrange for someone to deliver a couple of 20 lb bags of ice and dump them in the passenger compartment just before you leave on a trip. :madgrin:
Well, temperature has little to do with mileage your getting, if your commute is just over 1 mile each way. Is that what you are saying? If that is the case, getting 45 to 49 mpg is excellent. At any temp. Without extraordinary measures, a 2nd Gen Prius needs at least a 10 mile trip to get better than 50 mpg performance.
I don't know that it really qualifies as a commute, but I do happen to live just about a mile's drive from my main office. On the job I drive 20-40 miles in the city and I am generally able to plan the longest trip first to get everything warm. I'm not particularly concerned about the MPG I am seeing this first month. I'm more hopeful that I can do things to keep it in good condition and avoid expensive catastrophic failures after I cross the Toyota Certified extended warranty and the service plan my wife insisted on.
From a fuel economy standpoint, the best thing is to keep the battery from getting too hot while parked. The simulator findings I linked in my previous post assume a battery within normal operating temperatures. A hot battery will cause a fuel economy hit, especially at low speeds. Above certain temperatures (104F or so, some suggest), the car reduces substantially its battery usage. As Hyo says, park in the shade. I use WeatherTech window deflectors on the fronts so I can keep the windows cracked while parked without worrying about sudden thunderstorms. I also have my windows tinted. It's true, as others suggest, that running the AC will help cool the battery. But that's a slow process. The battery is a large thermal mass and cools (and in the winter, warms) very slowly. Prevention is best. Another thing comes to mind -- not a fuel economy issue but much more important: There have been a few inverter coolant pump failures, seemingly more frequent in warmer climates such as yours. For that reason, some recommend replacement as a preventive maintenance measure around 100K miles. Here's more: http://priuschat.com/forums/gen-ii-.../65173-how-replace-inverter-coolant-pump.html Inverter Pump
