Cold engine

[sammd]

I was wondering out of interest, is it more economic to start your engine and leave it running for 5 minutes in the morning to warm up before you drive it (also for the purpose of melting ice) or to drive off with a cold engine? Thanks for any answers.

[Impret-Sir]

In terms of simple fuel economy it must make sense to drive off immediately. However, there are other considerations, I always allow my engine to idle for about a minute before driving off, to allow the oil to circulate up to the top of the engine and to allow it to warm up a little. I believe this minimises engine wear at its most critcal time, when the engine is cold and the oil is thick. I then drive away but avoid using more than half throttle until the thermostat opens. As you say, if you allow it to run when the car is frozen then it will help melt the ice off the windows, I always run the engine while I scrape the frost off, with the screen blower and rear heater going, then it is safe to drive away.

[c00ky83]

It depends if someone nicks your car or not. Mind you, I thought you shouldn't do it - it can't be good having the heaters on full with no moving air coming in.

[sammd]

Thanks Impret-Sir (Impreza?). Good tip on the 1 minute idling.

c00ky83 - I have 2 keys :)

[d0gsb0dy]

The engine-wear bit doesn't apply to diesels, as oil is being injected into the cylinders and not raw petrol. This is why diesel engines tend to last a lot longer than petrol. I have a 1.8d fiesta with 120,000 on the clock. It doesn't burn any oil and is not showing any signs of wear. I let it idle on cold mornings and, like sammd, I have 2 keys so that I can keep it locked while it's running.

[qapmoc]

Isn't it illegal to leave a car with no driver while the engine is running ??

[Toureman]

No, it is not more economical!

You should drive gently until the engine warms up though.

[Toureman]

To answer qepmoc, it is illegal to leave an engine running with no one in the car but only on a public highway.

How could garages mechanics ?diagnose engine problems if they had to sit in the car

[sammd]

Also as the car is locked there is no chance of anyone getting in or the car moving. (It is also in the drive).