It's taken a while for carmakers to begin fitting stop/start systems to U.S. vehicles, such systems' benefits not really advertised to consumers in a car's EPA numbers.

In the real world though, many manufacturers say the systems can save you significant amounts of fuel--particularly if you regularly commute in heavy traffic.

Jaguar has joined other luxury carmakers in offering the system on a selection of its models.

When pulling to a halt, the system cuts the engine to save fuel and reduce emissions, during what Jaguar terms "ECOStop". It then restarts as you lift your foot off the brake--so the engine is already running before you press the gas pedal.

The benefits are fairly easy to understand--an engine that's off is an engine using no fuel and producing no emissions. And while Jaguar cabins are generally pretty quiet, it's even quieter with the engine off entirely. Until now, many carmakers have been reluctant to fit such systems, despite their benefits, as cars on the EPA test cycle spend too little time not moving for stop/start systems to take effect.

Naturally, there may be situations where you don't want the system to function, so the system is designed to perform differently depending on the conditions.

If it's too hot (over 104 F) or too cold (below 32 F) outside requiring the air conditioning or heating inside, the system remains on. This also applies to ambient cabin temperature, or if the driver has set the heating and ventilation controls to a high setting. If the hood is open, the driver turns the steering wheel or has their belt unbuckled, the system will also deactivate.

2013 Jaguar XJ

2013 Jaguar XJ

The driver can also switch off the system using a dashboard button--these scenarios and more can be seen in the video above.

Jaguar's Stop/Start uses a "Tandem Solenoid Starter", allowing independent starter gear selection and engine starting. A more powerful and durable starter motor replaces the standard starter.

The system is available on all 2013 Jaguar XF and XJ, V-6 and V-8 sedans, and will be standard on the upcoming F-Type sports car. It isn't available on 2.0-liter XF models, nor the older XK Coupe and Convertible lines.

But will Jaguar buyers take to the system in a way their BMW-driving counterparts didn't?...


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