# Why is my new (to me) car getting such lousy gas mileage? **URL:** \ **Category:** Factual Questions\ **Created:** [January 28, 2007, 11:47pm UTC](https://boards.straightdope.com/t/why-is-my-new-to-me-car-getting-such-lousy-gas-mileage/389891 "2007-01-28T23:47:29Z")\ **Posts on this page:** 6\ **Page:** 2
**Author:** ![Pushkin](https://avatars.discourse-cdn.com/v4/letter/p/ee59a6/32.png) [@Pushkin](https://boards.straightdope.com/u/Pushkin)\ **Post date:** [January 31, 2007, 9:45am UTC](https://boards.straightdope.com/t/why-is-my-new-to-me-car-getting-such-lousy-gas-mileage/389891/21 "2007-01-31T09:45:30Z")
[QUOTE=groman] The difference is most likely not sustained speed, but rather how you accelerate – I’m gentle but when accelerating I typically keep my foot to the wall until I reach the desired speed. When my stepdad started driving the Jeep again his gas milleage went back to 22 mpg. [/QUOTE] Indeed, which is why hybrids are designed so that electic motors do most of the acceleration and the gas/petrol engine handles keeping the car at constant speed, the accelerating is what puts your mileage up. ---
**Author:** ![scr4](https://avatars.discourse-cdn.com/v4/letter/s/59ef9b/32.png) [@scr4](https://boards.straightdope.com/u/scr4)\ **Post date:** [January 31, 2007, 5:10pm UTC](https://boards.straightdope.com/t/why-is-my-new-to-me-car-getting-such-lousy-gas-mileage/389891/22 "2007-01-31T17:10:57Z")
One other factor that nobody seems to have mentioned: in winter, it takes much longer for the engine to warm up. And until it does, the engine is running very inefficiently. This is a huge factor if you mostly take short trips - if you only take 5 mile trips, your engine may _never_ reach optimal operating temperature. And it doesn’t help to warm up the car before you start driving, because the car is using up gas while it’s warming up. The only thing you can do is to minimize the number of trips you take by combining multiple errands into a single trip. [QUOTE=Johnny L.A.] … coworker bought a Wrangler with a 4-cyl. engine because he thought it would get better mileage than the four litre six. What he didn’t think of though, was that on the freeway he was flogging the hell out of his four-banger while my (bigger, heavier) Cherokee was loafing along with its six. His mileage was much poorer than mine. [/QUOTE] Wouldn’t the 4-cyl vehicle get better mileage _if_ driven conservatively? I have a very underpowered car ('83 Mercedes 240D, 68HP and 3300 lb weight), and it gets poor mileage at freeway speeds. I get 30mpg if I only drive in the city (always under 50mph), and 24mpg for a 65mph road trip. ---
**Author:** ![Uber\_the\_Goober](https://avatars.discourse-cdn.com/v4/letter/u/58956e/32.png) [@Uber\_the\_Goober](https://boards.straightdope.com/u/Uber_the_Goober)\ **Post date:** [January 31, 2007, 5:20pm UTC](https://boards.straightdope.com/t/why-is-my-new-to-me-car-getting-such-lousy-gas-mileage/389891/23 "2007-01-31T17:20:11Z")
[QUOTE=Fear Itself] Is the weather really cold where you are right now? That will cause all cars to lose mileage, but it will improve during warmer weather.. [/QUOTE] Um, experience and science say, I think, that this statement is wrong. Colder air is denser. More air, more oxygen, more boom in the cylinder. Gasoline just ignites the oxygen. This is why cars make more power in colder weather. If they’re making more power, then they don’t need as much throttle input to acheive the same acceleration, therefore, less gas is used. Can I get a mechanic? Can I get a mechanical engineer? Can I get a motorhead? Looking for support to my unsupported claim here. 🆒 ---
**Author:** ![Uber\_the\_Goober](https://avatars.discourse-cdn.com/v4/letter/u/58956e/32.png) [@Uber\_the\_Goober](https://boards.straightdope.com/u/Uber_the_Goober)\ **Post date:** [January 31, 2007, 5:22pm UTC](https://boards.straightdope.com/t/why-is-my-new-to-me-car-getting-such-lousy-gas-mileage/389891/24 "2007-01-31T17:22:01Z")
ok, yep, I didn’t read enough of the posts. Never mind me. 😛 ---
**Author:** ![Schuyler](https://avatars.discourse-cdn.com/v4/letter/s/54ee81/32.png) [@Schuyler](https://boards.straightdope.com/u/Schuyler)\ **Post date:** [January 31, 2007, 6:53pm UTC](https://boards.straightdope.com/t/why-is-my-new-to-me-car-getting-such-lousy-gas-mileage/389891/25 "2007-01-31T18:53:11Z")
[QUOTE=Pushkin] Indeed, which is why hybrids are designed so that electic motors do most of the acceleration and the gas/petrol engine handles keeping the car at constant speed, the accelerating is what puts your mileage up. [/QUOTE] With all due respect, you’ve got this kind of backwards. A true hybrid (one that can run on gas-only, electric-only, or gas w/ electric assist) will use the electric motor at light throttle settings - such as when you are cruising around town. At heavy throttle, such as accelerating briskly from a stop or high-speed cruising, then the gas engine will kick in. Basically, it is not desirable to run the gas engine at very light throttle settings _in a hybrid_ because you are using a disproportionate amount of fuel just running engine. Two strategies in a hybrid, for example a Toyota Prius, to maximize mileage: 1. Accelerate briskly, which will cause the gas engine to run, then back off abruptly once to cruising speed, which will cause the engine to turn off and then the car will run on batteries. 2. Accelerate very gingerly (only practical in light traffic) which will cause the car to bypass the gas engine entirely. ---
**Author:** ![Pushkin](https://avatars.discourse-cdn.com/v4/letter/p/ee59a6/32.png) [@Pushkin](https://boards.straightdope.com/u/Pushkin)\ **Post date:** [January 31, 2007, 9:58pm UTC](https://boards.straightdope.com/t/why-is-my-new-to-me-car-getting-such-lousy-gas-mileage/389891/26 "2007-01-31T21:58:26Z")
The way I’d always heard hybrid operation described, the electrical motor was there to boost the conventional engine when needed, or to operate by itself at low speeds. The idea being that the petrol/gasoline engine is most efficient at steady, lower revs. I thought I’d second check myself (this being the Dope and not a pub chat!) and wikipedia came up with the following; > [@](#): > > The operation of the Prius can be divided into five (5) distinct regimes: > > (1) Electric vehicle mode (2) Cruise mode (3) Battery charge mode (4) Power boost mode (5) Negative split mode > > In (1), the engine is off, and the battery provides electrical energy to power the motor (or the reverse when regenerative breaking is engaged). Used for idling as well when the battery state-of-charge [SOC] is high. In (2), the vehicle is cruising (i.e. not accelerating), and the engine can meet the road load demand. The power from the engine is split between the mechanical path and the generator. The latter provides electrical energy to power the motor, whose power is summed mechanically with the engine. If the battery SOC is low, part of the power from the generator is directed towards charging the battery. Regime (3) is used for idling as well, except that in this case the battery SOC is low and requires charging, which is provided by the engine and generator. Regime (4) consists of situations where the engine cannot meet the road load demand, and the battery is then used to power the motor to provide a boost to the engine power. Finally, in (5) the vehicle is cruising and the battery SOC is high. The battery provides power to both the motor (to provide mechanical power) and to the generator. The generator converts this to mechanical energy that it directs towards the engine shaft, slowing it down (although not altering its torque output). The purpose of this engine “lugging” is to increase the fuel economy of the vehicle. From; [Wikipedia](http://en.wikipedia.org/wiki/Petroleum_electric_hybrid_vehicle) [Previous page](https://boards.straightdope.com/t/why-is-my-new-to-me-car-getting-such-lousy-gas-mileage/389891.md?page=1)