On my way to work yesterday evening, my Coop was clearly lacking a significant number of horses. It must have been around 30 degrees at the time, and it felt like I'd lost about 20/25% power! Now, I have read that warm air in the engine bay will cause a car to loose power, but can it really be that bad?

I had considered the issue to be something else, but when I left work at 4am and the outside temp had dropped to about 18 degrees, I'm happy to say all horses had returned to the stable. In fact, it's fair to say the road was all mine this morning 😏.

Anyway, anyone suggest the best way to prevent this? And why exactly does it happen?

Density of air and oxygen levels...higher engine temps etc....performance in a turbocharged car/the Coupe is reduced in hot weather.

Off the top of my head an Aquamist system may help?

1) Live somewhere cold

2) on an NA car, it's simply that hot air is less dense than hot and so contains less oxygen, which means less fuel can be burned and so less power. On a turbo, recall that air is heated when it's compressed. If it's too hot getting to the engine you'll get preignition and other nasties; the ECU backs things off to avoid your engine going bang.

3) possible cures: water injection, better intercooler, active cooling on the heat exchanger, driving at night...

I remembered a thread on this from years ago and recall posting about an article I read in Autocar on the subject. Here it is!

2006!!

North Yorkshire? - don't worry it won't last Longest day of the year it's downhill from here.

Yes, here comes the rain!

It's a breathtaking 17c up here at the moment.....

bonnet vents

Subaru style

It's the ONLY course of action.

That, or a radiator fan override switch...

The only reason Subaru's have a bonnet scoop is because the intercooler is on the top of the engine...

It's debateable whether they actually help to get the airflow where it needs to be if the intercooler is up front where it should be.

Getting the fans on earlier will only help when standing - when moving at a decent speed they do very little to help if anything at all.