6 replies to this topic

[thegreenhornet]

I've looked a few times on the forum for this but I can't really find anything that answers me question directly - I'm more trying to work out what's normal Mini behaviour and what needs attention.

I know that electrical drains cause the idle speed to drop slightly, but putting my (halogen) headlights on causes a drop of about 350rpm and the alternator to faintly whine. It used to be that the longer I drove it, the less this gap became, but this hasn't been the case since winter started and I had to use the headlights more.

Also - and I'm not sure if this is related or not - restarting the engine when it's still hot, after half an hour say, will also cause a low idle speed until I've run it down the road a bit. Is this the electrical drain from recharging the battery after I've run the starter motor? Or a tuning/carb/ignition issue?

All the electrical equipment causes the engine to run slower, but the biggest culprit is the lights, followed by the heater. Ironically the rear screen heater has almost no effect whatsoever, though it is a bit useless.

[Alex_B]

This is normal behaviour, and its why modern cars with AC have a over-ride to up the engine idle when the air con is being used to avoid it stalling

To minimise this you will have to look at all the connections and check they are clean and well connected, any resistance create at these connections will ultimately draw more current from the battery. The slight squeal you are getting could be a worn out fan belt or just it being a bit loose, I would tighten it up and see if the squeal goes, if not a new fan belt isnt expensive 

[KernowCooper]

Normal as the electrical load increases the idle speed will drop and the whine is the alternator working if its not the belt not correctly tensioned, or its worn out

Edited by KernowCooper, 28 January 2014 - 11:46 PM.

[Dan]

And the longer you drive the more charged the battery becomes so the electrical load reduces. The rear screen heater draws 5 amps, less if there are any broken tracks, so it won't have much effect on the total system load. This isn't because it's a Mini, it's because it isn't electronically controlled. Load compensation in a carb and dizzy engine relies on complex mechanisms driven by vacuum that need lots of setting up and regular servicing, everyday cars simply never had it. With an ECU running everything it's far simpler.

[thegreenhornet]

Thanks for the replies guys :) The alternator pulley sits slightly further back then the other two - could this cause the whine? The belt doesn't look that old. If so, do you think adding some washers into one side of the mountings do the trick?

[jime17]

The pulleys should all line up. The fan belt won't last if not. I can't imagine it does the alternator bearings much good either. The whine could be the belt being too tight which might be needed to compensate for the lack of alignment.

Edited by jime17, 29 January 2014 - 11:15 AM.

[thegreenhornet]

There's a job for the weekend then ;)