Quote:
Originally Posted by Clan
With all due respect you are supposed to change the plugs every 12000 miles 
except in recent years with petrol making a comeback it can be 36000 or 72000 miles . |
I know which is why i was astounded to discover/work out that the set in my 760 when i bought it had been in there at least 10 years and some 60-70k miles!
The fact they were still working as they should (despite the gap big enough to drive not just one bus through but a whole fleet) was even more amazing.
The reason i changed them again some 6k later when i renewed the plug leads is i had them sitting there and as i was already halfway there with changing the HT leads, decided it would save me a job later.
In terms of extended plug change intervals, i have heard of some models that are only specified (by the manufacturer) at 100k miles - at the same time the coil packs must all be changed - all 8 of each, plugs and coil packs!
As you might guess, that's on a Lexus V8 and the plugs are some special iridium jobbies, an eye-watering price each as are the coil packs from Toyota/Lexus.
However, those engines are designed to operate with iridium plugs and the plugs are designed to operate for the extended period.
The cost is still prohibitive though, a "normal" plug is also specified with a more normal interval of 12k miles which IMHO is a good thing for at least 2 reasons.
First, it means the plug can't seize in the head through electrolytic reaction and secondly, 8 (or even 9) normal plugs are a hell of a lot cheaper than 1 iridium thing from Lexus.
I no longer have the figures to hand but was told them by a friend a couple of years back when he bought an LS430, plugs (IIRC) were about £50 and coil packs about £80 each.
On a V8, that's a lot of money!
He bought 10 ebay special coil packs for £80 (on the basis one coil pack would fail quickly and one would be DOA so still had 8 good ones) and a set of normal plugs, being of the same mind-set as me that it reduced the risk of the plug seizing in the head.
All that aside, it doesn't solve the underlying problem on Lukes engine where it would seem 2 pots are running lean, causing the excessive gap to be created on two of his plugs.
