Is it cheaper to open the windows or keep the car air-con running?

Temperatures will stay in the mid to upper 30s this week

This week the Region is back into green temperature zones and will hover around a "comfortable" 35 degrees maximum for the rest of the week.
But whilst these sort of temperatures have us all running for the shade, what are they doing to our poor cars sitting out there all day in the blazing sun?

Its probably not much of a surprise for residents who have sat through a week of 40 degrees plus to discover that the heat of summer doesn’t do their car any favours.

But is there anything that can be done to beat the heat?
Temperature is the biggest problem, and when the temperature is above 35ºC the engine loses about five horsepower (or 15 in the case of some turbo engines), and the fuel consumption goes up by an average of one litre per 100 kilometers: in other words, around 1.40 euros, based on current fuel prices.

Apart from that there are other heat-related problems which can occur in the braking system (which wears out more quickly), the tyres (whose longevity can be reduced by 15%), the paintwork (which loses its shine), and the interior, where colours fade and  surfaces can become distorted.
 All of these effects are unavoidable, but there are some steps you can take to ensure that the following problems affect your car as little as possible.

1. The raised temperature of the engine’s air intake
Both diesel and petrol engines need air intake into the cylinders in order to burn fuel. However, when the air is hot it contains less oxygen, and this means that the fuel is burnt less easily: as a result the engine’s performance is affected. Can anything be done about this? No, but the downgrading of performance is reduced noticeably if your air filter is clean, so if the car hasn´t been serviced or the airfilter changed for a long time, get it looked at!

2. The mechanics of the cooling system are overworked
The function of the cooling system is to make sure that the engine doesn’t overheat above its normal running temperature of between 85 and 95 degrees. In summer it has to work harder, especially if the car is travelling at under 40 km/h: when this is the case the electric fan has to turn itself on more often, using up energy which would otherwise go to the engine itself. This translates into a loss of two horse power, which is not really noticeable on its own, but can obviously affect performance when combined with other issues.
Again, this is unavoidable, but remember that the cooling fluid should be changed every four years and you should check the level once a month. As long as it’s between the minimum and maximum marks, it should be OK.

3. The air conditioning is overworked
Vehicle air conditioning systems use a compressor which is activated directly by the engine, so when it’s running it effectively removes four horsepower from the engine’s performance.
This can of course be avoided simply by not using the air conditioning, but it’s not to be recommended! The loss of power is barely noticeable, and the increase in fuel consumption is under half a litre per 100 km: this is less than you would lose if you drove around with the windows open, and air conditioning is normally far more comfortable in extreme heat! What’s more, it has been shown that driving with the windows open is more dangerous.
Where the real savings can be made is by turning off the A/C and opening windows when having to drive slowly, ie in City environments, but of course, that just lets the fumes in, and is it really worth the savings when its 40 degrees outside?
Its also fractionally more fuel efficient to have the windows open when travelling at speed, and the A/C off, but not significantly, indeed there have been numerous studies into the subject measuring drag and resistance, and different experts have argued about points of a percentage, but the saving in fuel is negligible, if at all, so be comfortable, youre worth it..

- Tyres. In summer the tyres reach higher temperatures, especially at high speeds on the motorway. If there is insufficient tyre pressure the part of the rubber which is in contact with the road surface gets even hotter, and its longevity is reduced by up to 15%. For this reason you should check the tyre pressure every week, especially before long journeys.

- Upholstery. If you park in the sun for hours then the temperature inside your car can reach over 60 degrees, and this can cause the dashboard to lose its shape. In addition, the colours of the upholstery can fade, so so its obvious why parking spaces in the shade are so fought over, and why so many bank give away free  branded windscreen sunshades.

- Bodywork. Over time the paint loses its shine, whether it’s normal or metallic, and this process is accelerated if the car is parked in the sun for long periods. The plastic bumpers also lose their colour, as do the mirrors, the floor mats and the door surrounds, which can become cracked.

- Brakes. When we hit the brakes, the pads rub against the discs and heat is generated. In summer higher temperatures are reached and there can be overheating, which makes braking less efficient, shortening the useful life of the brake pads and deforming the discs. The fluid should be changed every two years, and in order to minimize wear and tear its advised that avoiding aggressive driving is a good habit to adapt, and use the gears to help slow down while driving downhill, not the brakes.

With temperatures regularly hovering around the mid-30s throughout the summer, the most sensible long-term investment is a car-port and the best way to save fuel and expense, is sleep all afternoon and go out in the cooler evenings!


Information discovered on  Autofácil.es whilst researching A/C versus open windows.

Are there any autobuffs out there who can improve on this information? Please feel free to use the comments box if you can help resolve the A/C versus open windows issue, which is probably one other couples have debated since fuel became so expensive.