Spark plugs for LPG LS430

[Abid221]

Hello

Getting my LS430 LPG converted. I've read that the spark plugs should be changed. 

Which ones do members recommend? And also how often should they be changed? 

Also do I really need to install the Flash lube system? 

Thanks 

[BMCWP]

I was told I needed "Platinum" Spark plugs in my Jaguar however I discovered that ordinary plugs worked just as well if changed during normal servicing and in 8 years had no issues - There may be a different way of doing things with the LS430's though so I would wait for somebody with actual knowledge to chip in 🙂

[messi]

You need denso or ngk irridum sparkplugs as recommended 

[Abid221]

1 hour ago, messi said:

You need denso or ngk irridum sparkplugs as recommended 

Thanks 

[The-Acre]

2 hours ago, messi said:

You need denso or ngk irridum sparkplugs as recommended 

Correct, but don't be fooled by the cheap ones from the likes of eBay, they can be poor imitations!

[runsgrateasanut]

I put Brisk Spark plugs in my Car in readiness for the changeover to LPG but as a Hail Storm in France turned the Car into a Golf Ball I won't be converting, as you know.

They've worked very well in my LS400 never missed a beat, but not tested with LPG or a LS430 so.............?.

[cruisermark]

I think I may of been a victim of this

[Herbie]

+1 for NGK or Denso iridium (15 years experience of LPG).

[Abid221]

4 hours ago, Herbie said:

+1 for NGK or Denso Iridium (15 years experience of LPG).

Where's the best place to buy these.? 

[The-Acre]

11 minutes ago, Abid221 said:

Where's the best place to buy these.? 

Eurocarparts have Denso iridium plugs for £10 each if you use their sale code, not sure how much less you can get the genuine article for elsewhere. 

[Bluesman]

On 3/13/2019 at 7:31 AM, Abid221 said:

Hello

Getting my LS430 LPG converted. I've read that the spark plugs should be changed. 

Which ones do members recommend? And also how often should they be changed? 

Also do I really need to install the Flash lube system? 

Thanks 

I have only ever used the standard plugs without any problem.

The answer to your Flashlube system is NO.

It's just another way of trying to get another hundred £s or so out of you. If your engine runs on unleaded petrol it will run on LPG with no problems.

[ScottC]

Jury seems to be out on this but LPG does burn a bit hotter than petrol so may be a bit harder on the spark plugs.

If you do buy the LPG certified ones remember to put a bit of snake oil on the threads before you fit them.

 

Scott

[Herbie]

41 minutes ago, ScottC said:

Jury seems to be out on this but LPG does burn a bit hotter than petrol so may be a bit harder on the spark plugs.

If you do buy the LPG certified ones remember to put a bit of snake oil on the threads before you fit them.

Not sure I'd agree with that. NGK are world leaders in their field and iridium plugs perform brilliantly on LPG or petrol so irrespective of whichever fuel I'm using, I'd always go for NGK Iridiums anyway.

[brendangeorge]

The standard spark plugs are fine - the LPG conversion does not need anything special.  I did nearly 200K on LPG in a 430.

The flash lube system is a waste of time - you don't need it.

Keep the LPG system well maintained and don't let any Muppets near it.

Keep an eye on the compression and look out for any rumbles - a loose spark plug on mine caused a burnt out valve.  This resulted in low compression and low speed rough running.  A V7 was the result and a 265K 15 year old car is not worth fixing at that point.

A mechanic forgot to nip up the plugs during a service - number 6 must have been looser than the others.........

To be fair the old crate had done its duty and owed me nothing.

I miss the old beast but I don't miss fettling it all the time :).

The new hateful object is awesome - get in, press the break, press the start button and go.

[Abid221]

7 hours ago, brendangeorge said:

The standard spark plugs are fine - the LPG conversion does not need anything special.  I did nearly 200K on LPG in a 430.

The flash lube system is a waste of time - you don't need it.

Keep the LPG system well maintained and don't let any Muppets near it.

Keep an eye on the compression and look out for any rumbles - a loose spark plug on mine caused a burnt out valve.  This resulted in low compression and low speed rough running.  A V7 was the result and a 265K 15 year old car is not worth fixing at that point.

A mechanic forgot to nip up the plugs during a service - number 6 must have been looser than the others.........

To be fair the old crate had done its duty and owed me nothing.

I miss the old beast but I don't miss fettling it all the time :).

The new hateful object is awesome - get in, press the break, press the start button and go.

Thanks for your advice. 

I'll be going ahead with a spark plug change as the previous owner who had it for 6 years hadn't changed then in his ownership. So perhaps a few new sets of sparkies might do it good. 

These ngk iridiums are bloody expensive. But I'll have to cough out the dosh to get it done with some peace of mind. 

 

[Bluesman]

On 3/17/2019 at 7:01 PM, ScottC said:

Jury seems to be out on this but LPG does burn a bit hotter than petrol so may be a bit harder on the spark plugs.

If you do buy the LPG certified ones remember to put a bit of snake oil on the threads before you fit them.

 

Scott

LPG burns lower than petrol.

[ScottC]

Yes, however a quick 'google' reveals that the cylinder head temperature is significantly higher with LPG due to the quicker burn time of the gas.

Running on petrol the cylinder temperature is reduced by the cooling effects of the petrol as it is injected. You don't get this with LPG as it is converted to a vapour

in the vapouriser before it is injected.

So it seems that the temperature around the spark plug will be much higher whilst the engine is running on LPG.

 

 

 

Although LPG produces less total heat ( it has a lower calorific value) that heat is released in a shorter time. The reason for this is that LPG is a 'perfect' gas at ordinary atmospheric temperatures whilst petrol vapour is liquid that has been forced to vapourise. The cooling effect of liquid petrol droplets is not present with LPG and the total heat is released more quickly. A greater heat 'spike' is the result. The engine will run slightly hotter, although the difference may not be large enough to show on the temperature gauge. Only the cylinder head temperature (CHT) will increase significantly (although not enough to cause any problems). Most cars do not have a device for monitoring CHT (unlike aircraft). A typical car temp. gauge measures coolant temperature only, which is much more of a general picture.

 

Leading on from that, it follows that an engine running on LPG will ' warm up ' more quickly than it would on petrol. Petrol consumption is extremely high when the engine is cold as a choke or excess fuel device (both giving a very rich mixture) must be used. LPG scores over petrol again, as this is not necessary. LPG does not need an artificially rich mixture and the engine warms (to its normal operating temperature, where it is most efficient) even more quickly as a result.

LPG has a high octane rating (it tends to give less 'knock') and is more easily and thoroughly mixed with air. One of the results of this can be a quieter and smoother running engine.

Scott

[Herbie]

+1 for what Scott says - I was reading that very same article and was going to quote it but he beat me to it.

[ScottC]

Not wishing to throw a spanner in the works here, but a copper or silver cored plug has far better thermal conductivity and much lower electrical resistance than a platinum or iridium plug.

So it should produce a better spark and wick more of the heat away from the combustion chamber.

I went through all this a bit back when I got my LPG LS430 and I found quite a number of references to platinum/iridium plugs being created to meet the demands of extended service life in modern cars, rather than them being any better than 'traditional' plugs.

I also found a number of references to platinum/iridium plugs being difficult/impossible to get out after extended mileages, so maybe a case there for using a plug that needs to be changed more frequently before it has a chance to get stuck. 

 

Scott

 

 

Material	Thermal Conductivity W/(m•K)	Electrical Conductivity MS/m
Silver	407	66
Copper	384	57
Gold	310	45
iridium	147	18
Platinum	70	10
Nickel	59	10

[Herbie]

24 minutes ago, ScottC said:

I went through all this a bit back when I got my LPG LS430 and I found quite a number of references to platinum/iridium plugs being created to meet the demands of extended service life in modern cars, rather than them being any better than 'traditional' plugs.

As far as I know that's the whole reason - to produce a good spark over the entirety of its longer life.

When changing plugs is a 4 or 5 hour job you don't want to be doing it very often so they're designed for longevity, not necessarily to be better with any given fuel.

[Bluesman]

11 hours ago, ScottC said:

Yes, however a quick 'google' reveals that the cylinder head temperature is significantly higher with LPG due to the quicker burn time of the gas.

Running on petrol the cylinder temperature is reduced by the cooling effects of the petrol as it is injected. You don't get this with LPG as it is converted to a vapour

in the vapouriser before it is injected.

So it seems that the temperature around the spark plug will be much higher whilst the engine is running on LPG.

 

 

 

Although LPG produces less total heat ( it has a lower calorific value) that heat is released in a shorter time. The reason for this is that LPG is a 'perfect' gas at ordinary atmospheric temperatures whilst petrol vapour is liquid that has been forced to vapourise. The cooling effect of liquid petrol droplets is not present with LPG and the total heat is released more quickly. A greater heat 'spike' is the result. The engine will run slightly hotter, although the difference may not be large enough to show on the temperature gauge. Only the cylinder head temperature (CHT) will increase significantly (although not enough to cause any problems). Most cars do not have a device for monitoring CHT (unlike aircraft). A typical car temp. gauge measures coolant temperature only, which is much more of a general picture.

 

Leading on from that, it follows that an engine running on LPG will ' warm up ' more quickly than it would on petrol. Petrol consumption is extremely high when the engine is cold as a choke or excess fuel device (both giving a very rich mixture) must be used. LPG scores over petrol again, as this is not necessary. LPG does not need an artificially rich mixture and the engine warms (to its normal operating temperature, where it is most efficient) even more quickly as a result.

LPG has a high octane rating (it tends to give less 'knock') and is more easily and thoroughly mixed with air. One of the results of this can be a quieter and smoother running engine.

Scott

All LPG engines start from cold on petrol and don't switch over to LPG untill engine has reached operating temp.

[Herbie]

4 hours ago, Bluesman said:

All LPG engines start from cold on petrol and don't switch over to LPG untill engine has reached operating temp.

Wrong I'm afraid.

Mine would start on LPG from cold although it wasn't really recommended. The actual changeover temperature was set at about 35^oC, which is a long way from normal operating temperature of about 90^oC. Usually it changed within about half a mile.

It's true that older systems should be run up to normal temp first but modern gas systems look after themselves very well on their own.

[ScottC]

Yes

On the hottest days of the summer my car is running on gas within a few hundred yards. No reason to think it wouldn't run immediately on LPG

if the electronics allowed it to. 

 

What system was yours? I have a BRC system in mine.

 

 

Scott

 

 

 

[Herbie]

1 minute ago, ScottC said:

What system was yours? I have a BRC system in mine.

The guy who did mine really knew his onions and rather than just use a complete kit from a given manufacturer he chose each component as being the best for the car.

It's more than three years since the conversion was done and it's over a year since we traded the car in for our current one and my memory isn't what it used to be but I do know that he chose a KME NEVO ECU, along with (I think) either Keihin or BRC injectors and possibly a KME Gold reducer - I honestly can't remember. What I do know is that it was truly superb and never gave an ounce of trouble.

[ScottC]

13 hours ago, Bluesman said:

All LPG engines start from cold on petrol and don't switch over to LPG untill engine has reached operating temp.

No that is completely wrong........LS460 conversion uses direct injection system for the LPG.

No vapouriser is needed to heat the LPG as on an indirect injection set up, the gas is injected straight into the combustion chamber.

So it starts and runs from cold on LPG.

 

 

Scott