LPG Spark Plugs - Fact or Fiction?

[LairdScooby]

Rover 25 1600 the iridium tipped ones last a good while but they are a Tenner
each

Easy to change on that motor and could buy 4 sets of nickle plugs for same cost...

Point here easy to understand and similarly applying to long lived tyres - Good that you don't have to change them so often, unless some other problem occurs such as punctures (particularly in tyre sidewalls) or kerb damage (case of some drivers). I prefer to change plugs during servicing anyway, less chance of them being stuck when it comes to changing, gives opportunity to check if cam cover gaskets are leaking oil into plug chambers.

Simon

Aaaaaahhh, that would be the K-series then. A tenner a plug is painful, i can buy a set of 6 NGK Copper Core jobbies for my Rover on ebay for a tenner. However, if i decide to go for something a bit more exotic then it will cost obviously cost me more.

Have to agree with Simon though, they're dead easy to change and you could buy 4 times as many sets for the same money of less exotic plugs that still do the job. Possibly they'd do the job better as they would be "fresher" - maybe something to think on? That was the whole point of me asking the question in fact for this thread.

I suppose in many ways i have my answer now and it is an answer of many ways too - basically i'll try the standard plugs and see how it goes. I often manage to blag trade price from my local auto factors especially if i buy plugs for both Rovers at the same time - must check to see what the Jeep uses! Might get even more discount!

[slickwix]

Although this thread is 5 years old I will throw another question in there which I've been researching the past 2 hours without success.
Basically, I have Bosch platinum FR7HPP33+ plugs recommended for my PETROL T4 V6 (2003 Multivn 2.8L AMV motor). I bought them a long while ago (before conversion) and in the interim have converted and discovered NGK LPG6 plugs as my best option.
OK, so I may as well install the FR7HPP33+ since I already have them, except on one website detailing these plugs (NB, only 1 of many websites) it specifically states 'Not to be used for CNG/LPG vehicles'.
Also, I do not know what plugs I'm running on now....very hard to get to on this motor AND have driven nearly 20,000km since conversion!
Is this a case of being too careful or is there an issue here that someone can enlighten me on (and save me 120 odd quid for 6 x LPG6 plugs)?
Thanks in advance,
Slick

[Gilbertd]

As a general rule, LPG and Platinum plugs aren't a good mix, whereas LPG and Iridium work fine. The NGK LPG plugs are Iridium but very expensive compared with normal Iridium plugs, have a look at www.sparksplugs.co.uk and see if there is an NGK Iridium option for your engine.

[LPGC]

That said, in most cases if an engine is recent enough (which could be quite old these days) to have platinum plugs fitted as standard, the manufacturer recommended platinum plugs are likely to give good performance on LPG. They wouldn't last as long as iridium.. but there's always the question when swapping from a plug that's proven to give good results in an LPG converted engine (of a certain engine model) to a plug that's yet unproved in the same engine model whether or not the unproved plug will give the same performance.

I still regularly see vehicles that have been running fine on LPG until the owner changed type of plugs during a recent service. Could say the owner might have considered the different type of plugs an upgrade but the engine didn't!

The situation is probably a bit better now than it was years ago, these days plug manufactures make/list more 'equivalent' types (nickle / platinum / iridium) and vehicle manufacturers that fitted platinum plugs as standard are likely to list an iridium plug as an upgrade... but plug manufacturers equivalents and manufacturer listed upgrade plugs by no means fully detract from the experimentation aspect of swapping to a different plug type.

Especially on an older spec engine, if plugs are easy to change (as they are likely to be on an older engine) a lot of owners prefer to stick to the cheap nickel plugs they know give good performance and are prepared to change them more often.

On a quite recent engine if a vehicle manufacturer fitted platinum plugs as standard but both the vehicle manufacturer and plug manufacturer list an iridium equivalent it's probably safe to assume the iridiums will give good performance and last longer than platinum.. especially if plugs are difficult to change it's likely such owner would be wise to swap to the iridium equivalent.

Between those two example situations there are many various combinations of older model engines with difficult to change plugs, newer spec engines with easy to change plugs, etc. Should the owner of an older vehicle on which it's a 5 minute job to change plugs risk buying plugs that cost 6 or 7 times as much as nickel plugs on the basis if they give good performance he won't need to change them as often... when he can't take the new plugs back if they don't give the good performance. Should an owner of a vehicle with platinum plugs that have lasted 20000 miles on LPG, plugs difficult to change, risk swapping to iridium - iridiums might last twice as long an platinum but if they don't give good performance he hasn't just wasted the cost of the plugs, he's also had to do the difficult plug change twice in quick succession.

The old-skool advice was that platinum acts as some kind of consumable catalyst in the LPG burn process (I realise the contradiction in terms there) hence it was said that platinum doesn't last much longer than nickle when running on LPG. I'm not sure where this came from or how true it is but it became generally accepted and I have repeated it myself. I've since wondered if that advice was started by installers who didn't want owners to fit platinum plugs in case owners brought vehicles back to them with misfires that they blamed on the LPG system but was actually a symptom of a poorer spark on older engines with weaker ignition systems fitted with platinum instead of nickel plugs (or even just fitted plugs of a none proven type for LPG on the respective engine).

Iridium does always seem to outlast platinum which does always seem to outlast nickel but this doesn't say anything about performance. If you change plugs from none iridium to iridium and still get the same performance as with the plugs removed you're laughing, it seems to be increasingly possible to do that.

[slickwix]

Thanks for those responses, greatly appreciated.
Unfortunately platinum plugs are what are recommended for this vehicle per that site (including all the cross ref's), or else the LPG6.
When I snoop about online I also discover the Denso VK16 "iridium tough" are also applicable, but at a similar price to LPG6 and with a "platinum chip on ground electrode", so don't know what to make of that (is it only platinum in the core that is the issue, or anywhere on the plug?).
In addition, a hard to get Champion plug is available that fits my criteria with a copper core!? A better price on these, but have read nothing regarding copper core and LPG. Tempting, but....hmm.
So, all in all, confusion is waxing here, but from what I've just read here I'm warming to simply using the platinum ones I already have and see how that fares. After all, I don't even know what's in there now, I only know they are probably ready to change.
Thanks again,
Slick

[Brian_H]

Probabbly a good idea to find out what you currently have since those are working well? Granted you have the others, so may as well fit them, but note whats currently in there once you remove them.

[LPGC]

Most platinum and iridium plugs have only the bottom (centre pin) electrode made from the precious metal. Denso make a range of 'double' precious metal plugs where both the centre electrode and overhanging bit (the anode and the cathode) have precious metal at the point of narrowest gap.

I have good results with Denso double iridium plugs on Nissan VQ35 engines (the standard plugs is an NGK single platinum plug), this isn't to say a plug of a different make/model to standard plugs for your engine (or to plugs you've found to give good results) would give good results on your engine.

Plugs are not difficult to access/change on a VR6 engine? I inspected plugs on a VR6 the other day, easy job.

[slickwix]

Doing the job tomorrow, so expect the update soon.
I've never changed plugs on this vehicle before, but judging from this 14 minute YT clip it kind of looks a bit tricky. These sideways V6 configurations always seem to have a bunch of spaghetti hoses to pin back, and that's after grill removal and radiator shift. Unlike the big open plan Chrysler v8's Im used to working on.
But thanks for that drop of courage,
https://www.youtube.com/watch?v=ewUx5UA1F-4

[slickwix]

So, the short of it is that the platinum plugs I had purchased were the exact ones I'd been driving with. By the looks of them they were way overdue for a change too. Straight swap.
But that job took 2.5 hours, so next time I'll be going for the longer life plugs.
Thanks for all the help.
Slick

[LPGC]

No probs Slick.
2.5 hours... Worse case scenario would be if you fitted iridium plugs which didn't work well so had to swap back to platinum.. it'd be 5 hours instead of 2.5 and 6 iridium plugs wasted. The iridiums would likely give great results but it would be unfortunate if they didn't lol.

[slickwix]

Good point.
Sadly, worse fates have befallen me regarding all things mechanical, but that's another (long) story....

[TNT]

My Golf Hated the NGK LPG plugs, Standard ones are perfect.

I would make the step up to Iridiums but the standard ones can had so cheep I don't mind swapping them out at a 9000-10000mile service, plug you have the added bonus of wanting to quickly check up on the HT leads and ignition coils or packs. my last set of leads lasted 30,000 miles and made a bit of a mess ( corrosion) of my coil back causing it to overheat. I would not have caught that if i wasn't changing my plugs every service. Turned out I had an iffy but not dead crank sensor too.