These plugs have been in my car for about 70k, so for the K's they seem like they in pretty good Nick.
http://i1191.photobucket.com/albums/z467/Shootmarty/IMG_0664.jpg
http://i1191.photobucket.com/albums/z467/Shootmarty/Plug.jpg
Just wondering if you guys reckon they are up for replacement, and what you'd put in there.
There were NGK R BKR5E-11.

I seem to remember these having a good rep.

http://www.brisk.biz/page.php?page=2600

NGK R BKR5E-11 are a copper cored plug from the front bank of the 3.5L engine, if I'm not mistaken. They look to be the right heat range for your application, and for 70,000 km show very little erosion. Just replace them with some new ones, same brand, same spec. Obviously LPG is kind on the plugs, I would keep things as they are.

I have a Pajero and a Magna - both on gas.I found that the original Pajero plugs - NGK PRF6 -11J were fine for the first 100000 km. The centre probe of these plugs is 0.6 mm dia the spark plug gap did increase in that distance - it was about 1.6 mm when they were replaced. The Magna had Chapion plugs and they gave no problems either.

After 100000 km, I had a few problems. I used AC Delco platinum plugs. NEVER AGAIN. Then I went back to the NGK's. At 200000 km, I fitted a new set of NGK's again, but had problems with the HT leads. I then bought new leads and plugs. I agonised over what to buy, but finally settled on NGK Iridium plugs. These have a centre electrode 0.4 mm dia, so I expect that they won't last as long as the originals. I have closed the gap slightly - 0.9 mm instead of 1.1 mm, to allow for the spark erosion of the electrode.

LPG engines require a heat range colder than normal petrol engines. This proved to be a problem because NGK Australia do not list any plugs colder than the PFR6 -11J, so I researched and bought my plugs (and leads) from the USA. NGK claims that the Iridium plugs give better performance and use less fuel. I believe in Santa as well, but I think that the low speed pickup was actually significantly better than the PFR6 plugs which had only 150000 km on them. With about another 150000 km on them now, I am still happy with them, although I still worry about how long they will last. Certainly, the thinner the probe, the stronger the spark and believe me, 0.4 mm is thin. These comments apply to both the Magna and the Pajero.

This is for the Magna, I take it?

Just use the same plug, but go one heat range colder - BKR6E-11. And as stated above, close the gap to 0.9mm. These can be bought very cheaply from the US on fleabay, with the $$ being the way it is. I bought 30 & it was less than $150 delivered to my door.

You could get onto NGK in the UK or on UK fleabay, where you can buy NGK LPG plugs to suit - why they're not available in OZ, I don't know; perhaps the LPG is different over there?

Good info there, Thanks Erad.
I'll give the Iridiums try.
Going to try the Penrite Oil for Gas engines as well

Bosch has platinum plugs for $30-40, which if they work is better than paying 4-5 times that for iridiums.

The numbers in this thread are huge lol. My old skyline would chew through plugs in 5000-10000km. I replaced them with oil just to be safe. Typical skyline issue though, platinums and iridiums often last people less time than the coppers lol.

SHOOT:
I replaced plugs in both the Magna and the Pajero at the same time. Same plugs used in both, although the Magna recommendations are for one grade hotter than the Pajero. The Magna is easy to replace compared to the Pajero. Cannot remember, but the Iridiums cost about $6 each from the US, plus a fair bit for postage.

im using standard heat range ngk iridiums in my tj (VSi) with ngk leads and when i checked them on my 130,000km service they looked to be in damn near new condition... this is after 60,000km (i installed them at 73,000km). so it looks to me as though the claims of 160,000km life expectancy (that i read in a trade journal) could be more than just manufacturers spin.

i got iridiums on mine cant remember brand got 4 prongs instead of one i think i paid about 250 for the 6 ive only done 20k on them 70k is pretty good i recken for lpg mate
mine gauranteed for 100k
next time ill get somthing cheaper and just replace more oftern as doesnt take much to change i also changed im leads at the same time
if you have no problem changing your plugs id say just keep using them for anothe 30k or replace the rear bank only

Thanks Alscall, Robceline, Ash, and everyone else.
I went the Iridiums, and supported Australian Businesses, Coz a guy spent the time, and his knowledge was T-riffic, also recommended the Penrite Oil range.
Gonna try and bribe Cracka to help me out too, goods for labour thingy, win-win.

The melting point of Iridium is over 2400 celcius, for platinum its about 1700 celcius and copper is about 1000 celcius. Iridium is also the most stable of those 3 metals (Iridium (and Platium) won't corrode, but copper does (ever seen the green tinge on copper left in the rain?)). The higher meting point is why Iridium plugs can have a fine tip - if you had a fine tip on copper plugs they would melt away. This is especially important with LPG, because LPG burns hotter.

Yes, but considering the original plugs still looked good after 70,000 km with no sign of reaching 1,000 degrees celcius, you are not going to notice the presence of the most expensive plugs you can find throwing sparks at the fuel/air mix inside your engine.

The other issue is longevity.

All things being equal, the Iridiums / Platinum will out last copper.

I'd personally go the Iridiums for the simple reason that I don't want to be personally changing (or paying someone to change) the plugs in the rear bank more often than I have to!

Here's a good tip for visually diagnosing a spark plug's condition:

http://www.ngksparkplugs.com/tech_support/spark_plugs/faqs/faqread.asp?mode=nml

The other issue is longevity.

All things being equal, the Iridiums / Platinum will out last copper.

http://www.ngksparkplugs.com/tech_support/spark_plugs/faqs/faqread.asp?mode=nml

That is true most of the time, but boosted performance cars often destroy iridiums/platinums quicker than coppers. Seems to depend on the car a lot, some people have them last 30k km easily, others I've seen burn through them in 3000km.

That is true most of the time, but boosted performance cars often destroy iridiums/platinums quicker than coppers. Seems to depend on the car a lot, some people have them last 30k km easily, others I've seen burn through them in 3000km.

Just remember the original copper plugs still look good at 70,000 km, so this engine obviously isn't hard on plugs.