Why do HT leads wear out?

[louismchuge]

It's not like you have to replace any other electical wiring in you house or car! Can a more clever person than I please explain! Thanks

[Altrezia]

Normal wiring doesnt sit in an engine bay with the heating and cooling so close to it. It's not the wires that wear out, but the sillicone(sp) outer.

[S3_Graham]

normal wiring doesnt carry the huge voltage either!

[louismchuge]

so if the cable shield looks to be in good nick theyre okay?

[marshalla]

louismchuge said:

so if the cable shield looks to be in good nick theyre okay?

Nope - the vibration of the engine & the thermal effects of repeated expansion & contraction can cause the internal conductor to break.

[louismchuge]

I see. Thanks chaps

[louismchuge]

One last question then - what would you say the average life expectancy is? I know they were changed on my car about 2 years ago. Only asking becuase I'm giving it a service and tune up before a long road trip

[The Lukas]

Just look for general condition. They should last years, difficult to say as type of car, mileage and other issues.

[tegwin]

Dont forget that every time you pull them off the plugs they are put under quite a bit of strain.... and if you use a "tool" to help lever the cable off chances are you might have accidentally nicked the insulator which can speed up the breakdown of the cables...

[louismchuge]

thanks again. I know it was a bit of a thick question, but i've not even given them the time of day previously and tinkered with everything else.

Emjoy your long weekends

[marshalla]

I usually replace every 12000 miles on the principle that they're cheap enough and easy enough to do - and better to spend a few quid extra than have an embarassing moment when I can't get hold of a new set. I always keep the last set in the boot though, just in case.

[freddytin]

Poor routing causing chafing / excessive heat / vibration.

Not pushed fully home into dizzy / coil/ plug terminal causing spark erosion /corrosion.

Use of WD40 causing insulation breakdown.

Heavy handed removal of leads causing stretching and breaks in the conductor.

Too large a plug gap causing leads to arc .

Dirt / oil will cause premature wear due to contamination of the insulation and provision of a low resistance path to earth.

Edit to add. Expect run of the mill leads to last 2 years before a drop off in performance.

Edited by freddytin on Friday 30th April 14:35

Edited by freddytin on Friday 30th April 14:38

[madrob6]

Mine are knackered because the insulation has split. They are 27 years old though so I can let them off, a new set costs something disturbing close to £100 though

[Munter]

marshalla said:

I usually replace every 12000 miles on the principle that they're cheap enough and easy enough to do - and better to spend a few quid extra than have an embarassing moment when I can't get hold of a new set. I always keep the last set in the boot though, just in case.

12000 miles! The ones on the MX lasted ~70,000 and the 2nd set are still going strong at ~120,000.