Quote:
Originally Posted by michael
Not sure if the same applies to the svx but in my outback when you have the air set to defog it uses the ac to remove moisture on the windshield. For those looking to increase mpg you may want to use the degog setting sparingly. I'm too lazy to look for the thread on fuel saving tip but if you're following it you may want to add this.
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This is a good point Michael.
Just for the sake of the good running of your aircon system you should run the system in defog or defrost at least once a week in the winter. This ensures your compressor stays in good working order. It is assumed you will use it fairly often in Summer to keep the car cool.
Auto Express in England ran some comparative tests recently in search of economy. They used a diesel car for the tests, I suppose it is possible a petrol car may have given different results [because the diesel engine has more torque available at low revs compared to a petrol engine].
Anyway they found that most of the things we are warned against made very little difference to overall mpg. These were things such as driving with a roof rail, driving with windows open, tires too soft etc. These only made 1 or 2 mpg difference over the test course.
Driving with the aircon on made a major difference around town, but not a great difference on the highway. Aircon made a 5 or 6 mpg difference in town and a 2 mpg difference on the highway.
This is all related to revs and engine output. Say for instance the SVX engine makes 200 hp at 5000 rpm. In broad terms it will be only putting out 1/5th of this at 1000 rpm, approx 40 hp. We all know the SVX tends to run in 4 range even at low speeds in town. Well at these speeds the engine is giving out 40-50 hp.
When the compressor is on it soaks up 5 hp to drive it, whether the engine is doing 1500 rpm or 5000 rpm.
So at town speeds it is using up 10% of the available power. All the time. So the mpg suffers.
At highway speeds the engine is probably making 120 hp, maybe more, so the 5 hp for the aircon pump is less of a hit.
It does actually pay to switch off the aircon if it is not required.
Joe