[R218is]

Hi, i have just done a full service on my car today and was thinking of changing the HT leads. Does any one know how often they should be changed? The car is just over 6 years old now and has done 45k.

I have had no problems starting/misfiring but just thought a change might improve mpg/peformance.

What do you think?

 

[Rover_King]

If there old then I suppose replacing them is wise.

 

[Obertelli]

It won't improve mpg/performance, but at six years old the materials in the leads will be degrading.
Eventually this leads (no pun intended!) to poor starting & misfires. If there are none of these symptoms yet I'd suggest keeping your eye out for a bargain set of OEM quality leads and buying when it suits you. If your leads are breaking down you probably won't find much evidence until the autumn when you face cold damp starting once again.
Try to replace them before any symptoms though as misfires can damage your catalytic converter.