Car-related debates

Let’s stick with this theme, shall we? If all goes according to plan, I’ll have a new car by the end of the week.

In the meantime, two car-related topics have come up in my conversations recently.

Cooling down, slowly

My friend Nan and her boyfriend have been arguing about the effect of aircon on your car’s power. He says (driving a 1.4 litre Golf) there is no discernable effect, as he can see no loss of revs – not even when trying to accelerate uphill with the aircon blasting.

The Gilb (and Nan and the rest of humanity, no doubt) believe otherwise. The Gilb says he loses 200-300 rpm if he turns the aircon on, which is especially noticeable when driving up a hill – on a flat stretch of road, no difference is really felt. I will have to experiment in my new car, as my dear Max does not have aircon.

Vaguely related: A while back, I came across an article discussing fuel efficiency and cooling down your car, regarding whether it is more fuel efficient to use aircon, or drive with your window open (creating drag). It claimed that at speeds above 70km/h, you should use aircon as it becomes more fuel efficient.


More bang for your buck

Over my driving life, I’ve made use of petrol from all petrol stations, and have observed a curious thing: some petrols (BP, Shell) get you further than others (Engen, Caltex, Sasol). At first I thought I was imagining things, so I started keeping a record of the mileage I got out of tanks filled with different petrol brands (in fact, damn! Another graph I could have displayed for my last post!), and the results consistently showed that BP and Shell (although in the latter’s case I have substantially fewer data points – their petrol stations are few and far between) get me almost 100km extra out of a tank. The fact that both these petrol brands do the trick almost confirms the observation for me, as BP and Shell share the same refinery (Natref, for those who care) which means the fuels refined there would share identical compositions (except for certain additives which are added later). Now, I know how variations in petrol can affect performance, but I have yet to do research to understand how they can affect fuel economy.

I forgot about this observation (other than subconsciously always choosing BP/Shell stations to refuel at) until the other day, when the Gilb mentioned that both he and a colleague had noticed different fuel mileages out of different petrol brands – although they said they’d noticed it with Shell only, not BP. They also claimed to notice better performance from Sasol petrol, and swear that this is not blind allegiance to their employer, but fact. (I wonder if the two factors, fuel economy and performance, are inversely related?)

I sheepishly have to admit I’ve not ever noticed a performance difference, nor did it occur to me that there even might be a discernable difference in the performance of fuels, despite the fact that I’ve seen advertising where brands have tried to differentiate themselves on the performance of their fuels. Interestingly, I’ve not seen any ads that I can remember that claim to get better mileage. In a world of ever-rising fuel prices, I find that a mighty strange thing.