Hi All,

I currently have NGK plugs fitted.

Is there any benefit from changing them?

Only if they are worn out and need changing. Stick with the recommended NGK plugs and change every 10-12,000 miles. If you want to swap to the Iridium equivalent, they will last longer (about 40,000 miles) but cost more than 4x the price so you aren't really saving anything.

Richard, ever heard of these ones? They are from Poland (you happen to be there once and awhile) and I was told they seem to be good.
These are the ones for Mr. Lucas:
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and these should be for Bosch:
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I have never heard of them.
Tony.

Neither have I. There are a number of different LPG specific plugs out there, the Brisk silver ones that seem to cause more misfires than Champions on most cars that people have tried them in and the special NGK ones. Personally I don't think it worth trying anything other than standard and I know that Vauxhall/Opel engines which were available on LPG as standard will only run on the original plugs.

Having seen the spec for the NGK ones, they are Iridium tipped but don't seem any different to the normal Iridium plugs other than being marked as for LPG and costing a lot more. The GEMS standard plug is the BRP6ES which last around 10,000 miles and I get them for £2 each, the Iridium BPR6EiX which lasts around 40,000 miles at £6 each and the LPG2 at £14 each which I doubt will last longer than the standard Iridium. Although in the long run the Iridium works out slightly cheaper, I use the standard ones and change the plugs every time I change the oil and filter.

Thanks Richard.

On the subject of spark plugs, what gaps are people using on LPG? Some people seem to say the standard gap and some seem to say reduce by 0.2mm.

I use NGK BPR6ES on my Thor aswell, and they seem to run fine, both on Petrol and LPG.

I haven't used Champion plugs in ages.. think they may have been in mine when I first bought it, but never since!

Gap - I used the standard gap of the NGK'S on my Thor.. the manual says to not gap them and leave them as standard out of the box. I checked my new ones and they were all just under 0.9mm from memory

I read somewhere - possibly http://www.lpgforum.co.uk - that you should gap them down to 0.7mm, and when I did that it made quite a difference. I'm still on the set of plugs I fitted not long after I got my P38, so I suspect it's probably due some.

0.7mm equates to 27 thou which is slightly wider that the standard 25 thou that plugs always used to come gapped at, 0.9mm is 35 thou which is about standard for a modern car with electronic ignition. I've never gapped mine down but may try it next time (if I remember) and see if there's any noticeable difference.

Martyuk wrote:

I use NGK BPR6ES on my Thor aswell, and they seem to run fine, both on Petrol and LPG.

Ditto

Just make sure they fit first!
https://rangerovers.pub/topic/305-resurrection-vogue-se-a?page=2#pid4215

Ferryman wrote:

Martyuk wrote:

I use NGK BPR6ES on my Thor aswell, and they seem to run fine, both on Petrol and LPG.

Ditto

I gap my NGKs to 0.7mm but that's standard for my Jeep. Haven't changed any plugs in the Range Rover yet. I vote for standard plugs, standard gap - and NGK are top of the heap. LPG does need a decent spark, so you might notice a shorter service life but nothing that makes the super expensive "LPG specific" plugs worthwhile.

No expert on plugs or chemistry but can say what I've noticed, my point of view and what the wider consensus of opinion seems to be.

If you're not sure what make of plugs to fit on any given vehicle, the NGK equivalent to whatever is standard is generally a good bet, not really relevant if NGK is standard.

Single pronged plugs are usually the best bet on LPG, unless standard plug has more prongs. General take on this seems to be that the extra prongs shield the mixture from the spark.

A lot of modern vehicles use platinum plugs as standard, platinum is supposedly consumed during the burn process of LPG because it acts as a catalyst (in the LPG burn process). While I'm sure iridium will last longer than platinum (it's a harder metal), I don't see any problems with platinum plugs in LPG engines, though they do wear out a bit quicker than running on petrol. At school I was taught something that acts as a catalyst aids a process without being consumed itself... and there is platinum in catalytic converters anyway.

LPG needs a hotter ignition source than petrol but I would think any electrical spark should be hot enough, so I don't tend to go with theories that refer just to spark temperature. Where coil voltage is marginal for making a spark jump across a plug gap, a spark may be much less likely to form running on LPG which is a dry fuel compared to running on petrol, so closing the gap is likely to help make for a good consistent spark. For any given condition in an engine cylinder, coil voltage needs to rise to the point at which a spark will jump the gap, so closing gap can also slightly advance ignition timing, I would think a negligible effect. No harm on most engines from using a slightly narrower gap than standard, gap will increase as the plug wears anyway (used to be common to gap points just a bit narrow knowing that soon gap would be to spec). Probably no big gains to be made from different plug types and gaps, as long as there are no misfires.

Used to be fairly common to have to close plug gaps, these days seems much less common, probably due to the vehicles we convert becoming later year models with stronger coils but never had misfire problems with P38s except in cases of worn ignition system components. If I had a P38 I'd fit the NGK's and gap them down a bit.

Having said all the above, I recently did a favour for a mate, changed the plugs on his petrol only Mondeo ST220 with Duratec V6 just for the cost of the bits. He'd had the plugs changed 6 months back and gave me the impression it had run OK since then until recently, so I had to wonder if the garage had changed the 3 rear cylinder bank plugs which is a manifold off job (front bank easy access without manifold off). I drove it in high gear at low speeds high loads to make it misfire and bring on the flashing MIL light, then OBD pointed to misfire cylinder 3, which is the right side rear plug. Getting the plugs out I noticed that 5 were new NGKs but the one with the misfire was an old original type Motorcraft plug. I changed them all for new NGKs, same spec as the 5 NGKs that came out, NGKs supposedly the equivalent to the Ford spec plug. It seemed fairly obvious that I'd found the problem (the plug that hadn't been changed) and I nearly didn't even bother testing it, but I did test it and it still misfired! Then my mate told me he'd had no problems with the car until having the plugs changed last time, and he'd been back to the garage about the misfire twice but they gave up when they found no OBD codes. Now I re-gapped all the plugs (closing) to spec (not pre-gapped to suit the Mondeo) and fitted new leads (his idea). The car now drives well under nearly all conditions but I could still force an occasional misfire at very low rpm near full throttle (few people would drive like that normally), and I reckon this will be due to the NGK plugs not being as good in this engine as the Ford recommended plugs, putting the Mondeo V6 in the same bracket as the Vauxhall engines Gilbert mentioned... but I only learned this while messing with plugs on this car, and since I have converted loads of the same engine in other V6 Mondeos and V6 Jags without having to even consider plugs, can read into this that standard plugs are the best bet on this engine on either fuel and NGK equivalents problematic even on petrol (on this engine).

Simon