99 RON Fuel and Spark Plugs

[Ozzay]

As you guys probably know I have had the IS250-SE for a bit more than a year know and have been floating through these forums getting your good help on most things.

In the service history the spark plugs were changed at 62,000 miles and the cars currently on 92,000 miles.

Everythings been in order and been maintained. Last time done an oil service Mobil ESP 5W-30 in August but have not done more than 3000 miles since and trans fluid 5L change in JULY.

I've been using Shell 99 mostly 90% of the time with the odd BP or alternative super fuel.

Noticed over a few months that Shell 99 has a bit of jerky gear change not majorly and BP has been quite smooth.

Oil definately fine and gearbox etc. Cars perfect.

Do you guys think this has something to do with the spark plugs? They were last changed in 2018 from the previous owner/garage and I can only assume they are the Denso ones mentioned in the spec.

Anyone had any similar experience? Do you think I should change the plugs?

[scudney]

Wouldn't have thought it would be the spark plugs if they are the recommended ones as apparently they are good for 100,000 miles,

[ColinBarber]

Worth pulling a plug to check it is the right model and not a Denso fake to put your mind at rest. 

[dephrank]

Isn’t 99 RON a bit too much for the 250? Mine says 95-97 Ron only. The car needs a good flooring sometimes to clear up the cobwebs. 

[Linas.P]

Fuel should not impact your gear changes. As for spark plugs - assuming they are correct plugs they should not be a problem either, after just 30k miles.

So generally speaking, anything to do with gearchanges will be related to gearbox itself. Perhaps disconnect the Battery to clear what it has learned (clears ECU memory)? 

1 hour ago, dephrank said:

Isn’t 99 RON a bit too much for the 250? Mine says 95-97 Ron only. The car needs a good flooring sometimes to clear up the cobwebs. 

That is not how octane works. Higher number does not mean more "potent" fuel, it just means fuel is more resistant to pre-ignition... so it is almost opposite, the higher is the number the "worse" it burns (at least by itself). 

[dephrank]

17 minutes ago, Linas.P said:

That is not how octane works. Higher number does not mean more "potent" fuel, it just means fuel is more resistant to pre-ignition... so it is almost opposite, the higher is the number the "worse" it burns (at least by itself). 

Thanks for the info. Didn’t know that. 

[eleveneleven]

Take it to Lexus for a Gearbox drain and Fill, costs around £180, makes a noticeable difference to the way the gearbox behaves. 

[Linas.P]

19 minutes ago, eleveneleven said:

Take it to Lexus for a Gearbox drain and Fill, costs around £180, makes a noticeable difference to the way the gearbox behaves. 

He said it was done in July... unless it was done wrong.

[Ozzay]

1 hour ago, eleveneleven said:

Take it to Lexus for a Gearbox drain and Fill, costs around £180, makes a noticeable difference to the way the gearbox behaves. 

Done the full replacement. 5Litres and gasket seal with new filter. Definately could see a difference.

But again, this is definately a fuel thing I have noticed where BP 97 feels smoother (not quieter initially). When you put your foot down BP fuel will hold lower gears longer where as Shell 99 would change the gear up earlier unless you decided to press mucher harder or go manual mode.

Its not majorly jerky, its just a slight jerkiness when you decide to take notice.

I thought oil and filter but no that was recent.

Fuel economy locally is about 22-25 but again that's short half mile journeys start and stop no chance of warming up.

On a combined medium/long 32-35. Pure long drive it does deliver at minimum 40mpg and I have seen it do 45 mpg.

I will check the sparks again but it has been 4 years since changed and I suppose I have driven it hard when warm half the time.

I have a friend with a garage so not an issue on price to change them I would not be able to on these streets too much havoc on the road for me.

In the manual it says "95 or higher" (fuel)

By the way I am using 5W30 oil anyone ever used 20W-50? Even though the manual says preferred for 5W30.

Sparks: DENSO FK20HBR11

By the way a side question, anyone ever bothered with DIFF oil.

[Ozzay]

On 2/20/2022 at 10:32 AM, dephrank said:

Isn’t 99 RON a bit too much for the 250? Mine says 95-97 Ron only. The car needs a good flooring sometimes to clear up the cobwebs. 

Mine says 95 or higher but I will be even more limited since E10 is a no.

[Linas.P]

30 minutes ago, Ozzay said:

Done the full replacement. 5Litres and gasket seal with new filter. Definately could see a difference.

But again, this is definately a fuel thing I have noticed where BP 97 feels smoother (not quieter initially). When you put your foot down BP fuel will hold lower gears longer where as Shell 99 would change the gear up earlier unless you decided to press mucher harder or go manual mode.

Its not majorly jerky, its just a slight jerkiness when you decide to take notice.

I thought oil and filter but no that was recent.

Fuel economy locally is about 22-25 but again that's short half mile journeys start and stop no chance of warming up.

On a combined medium/long 32-35. Pure long drive it does deliver at minimum 40mpg and I have seen it do 45 mpg.

I will check the sparks again but it has been 4 years since changed and I suppose I have driven it hard when warm half the time.

I have a friend with a garage so not an issue on price to change them I would not be able to on these streets too much havoc on the road for me.

In the manual it says "95 or higher" (fuel)

By the way I am using 5W30 oil anyone ever used 20W-50? Even though the manual says preferred for 5W30.

Sparks: DENSO FK20HBR11

By the way a side question, anyone ever bothered with DIFF oil.

DENSO FK20HBR11 is correct, question is if they are genuine. 

20W50 would be terrible choice of oil, especially that 20 part, this is sort of "classic" car oil, definitely not for modern engine and would result in excessive wear when cold (which is already the most damaging part of the engine cycle). I have used Mobil1 ESP extra long-life 0W40 with great results. In short the lower is the the first number (cold) and the higher is the second number (warm) the better. So 0W40 or 5W50 is good oil, 20W50 is trash oil (except of very limited classic car niche), the only issue with "multi-grade" oil (all oils nowadays are multi-grade) is that the wider is the gap, the more additives there are in the oil, and the more additives the quicker the oil will lose it's spec. For example 5W20 could have very thin base oil and relatively small amount of additives, so even when additives fail it will remain thin oil, which is good for shorter trips and colder weather... say after 6 months it will be 10W15. However, if you take 5W50 (which is considered racing oil - protecting well when engine is warm hence W50), then it will degrade into something much thicker, because base oil for it is much thicker, say 30W40, which is horrible for cold start. 

In short if you go with "aggressive" multi-grade, then you need to replace it more often, ideally every 3000-6000 miles or 3-6 month, otherwise stick with good quality 5W30. I would replace it every 6000 miles anyway, because direct injection engines are picky on oil.

[Mr Vlad]

Excellent post Linas 👍 

[is200 Newbie]

So if you can tell that the plugs have been changed, can you tell if the upstream oxygen sensors have been changed (located in the engine bay on the exhaust) - could be they are on their way out as they will, together with the downstream ones determine what the fuel/air mix is by the ecu and could, as you are saying its not that noticeable an issue, be causing it?

[Linas.P]

But why would that be causing harsher shifts? Poor fuel economy perhaps, bit sluggish start, especially when cold - that would make sense. As well it won't matter what fuel is being used, it would be either continuously poor or all-over the place is intermittent. But if it is harsher gear changes with only particular fuel, then it kind of doesn't make sense. 

Sadly I can't provide the answer, but I am thinking along the lines that fuel and shifts are unrelated, and harsh shifts are rather coincidence related to something else. 

[Ozzay]

3 hours ago, is200 Newbie said:

So if you can tell that the plugs have been changed, can you tell if the upstream oxygen sensors have been changed (located in the engine bay on the exhaust) - could be they are on their way out as they will, together with the downstream ones determine what the fuel/air mix is by the ecu and could, as you are saying its not that noticeable an issue, be causing it?

I cleaned the MAF around April/May last year with MAF cleaning spray. Noticed better throttle response slightly but that's it.

Reset the ECU around 3-4 months ago just because I thought give the car a reset post fluid change and of course from my other few threads you would know I hate this car when it goes to first gear under 7mph but its so much better now especially when warm. As in it will drop to 1st but going back to second its just quick and not much overreving going on. But this is another story its just certain bumps are so disgusting I have not choice to slow down on a crawl, its also to do with the suspension type, in a BMW 1 series I could fly over them without feeling much but IS its likes you know it will jump a little.

 

[Linas.P]

3 minutes ago, Ozzay said:

I cleaned the MAF around April/May last year with MAF cleaning spray. Noticed better throttle response slightly but that's it.

Reset the ECU around 3-4 months ago just because I thought give the car a reset post fluid change and of course from my other few threads you would know I hate this car when it goes to first gear under 7mph but its so much better now especially when warm. As in it will drop to 1st but going back to second its just quick and not much overreving going on. But this is another story its just certain bumps are so disgusting I have not choice to slow down on a crawl, its also to do with the suspension type, in a BMW 1 series I could fly over them without feeling much but IS its likes you know it will jump a little.

Yes most Lexus for some reason don't like speed bumps, any sort of bump which hits both wheels at the same time. Same thing in RC and IS mk3... although I would not advise flying over the bumps in BMW 1 series, because one day both spring may collapse. Happened to my friend on motorway and it was not very funny 😄  

[Ozzay]

4 hours ago, Linas.P said:

But why would that be causing harsher shifts? Poor fuel economy perhaps, bit sluggish start, especially when cold - that would make sense. As well it won't matter what fuel is being used, it would be either continuously poor or all-over the place is intermittent. But if it is harsher gear changes with only particular fuel, then it kind of doesn't make sense. 

Sadly I can't provide the answer, but I am thinking along the lines that fuel and shifts are unrelated, and harsh shifts are rather coincidence related to something else. 

You know the weird thing is. When the car starts cold on any fuel type. The shifts are dead smooth. Its when the cars warming up and believe me I drive under 2000 revs like a grandma until it hits the middle of the temp range.

Definately a fuel thing.

I can only think of spark plugs and/or another ECU reset perhaps. But yeah BP is just different. Before I used to hate BP but now I am thinking it suits the car better in the way the gears shift. But saying that I had no issues pulling the car off standstill on Shell 99.

The previous owner was quite meticulous. Only owner of the car since new and always took it to mostly the same garage and they wrote everything in the service manual properly.

If I can get 6 original Densos cheap I might consider changing them. Are NGK any good I read that they have better tolerance for temps but if they are both iridium can't say if either one matters much.

Don't really want to service the car oil seems fine and that will be In JULY.

So maybe:

Clean throttle body

Change Air Filter again

Sparks

ECU reset

 

@Linas.PTalking about the suspension I have had it for over a year I am generally a careful over bumps but don't care when it comes to general roads no matter how bumpy or poorly surfaced they are in the UK. Went North Wales last year hit some B roads everyday really pushed it around hard, great fun, and yet no knocks no rattles just nice as I got it when I hear it take over a few humps. Dunlops on your rec are still about 8mm minimum.

[Linas.P]

NKG are ok as a brand, but not suitable for IS250. In IS250 it is best to stick with Denso, they are pricey, but in grand scheme of things not too bad:

https://lexuspartsdirect.co.uk/product/lexus-is-phase-2-six-spark-plug-kit/

 

[Ozzay]

Only fault I have had with the car that came up on the dash was the washer fluid 🤣

I will probably check something via OBD reader.

[Malc]

16 hours ago, Ozzay said:

If I can get 6 original Densos cheap I might consider changing them.

good god ........... you're changing the plugs maybe every 100k miles or 10 years is it ???  why on earth worry about scrimping to save a few bob to the possible detriment of your sanity and using your car satisfactorily

Malc

[Mr Vlad]

I've read this thread a few times and I still don't get that how different petrol can dictate the auto box as to when it changes gear. I think it's like a placebo effect.

You say you've changed the oil. Have I miss read something ? Engine oil or gearbox oil?

Engine oil won't affect gear changes but gearbox oil will. I've read that in one or two cases where the owner has had a gearbox oil change and all kinds of hell broke loose. 99% of those who have had gearbox oil change have had no I'll effects. One wonders then if you got your gearbox oil changed was it done correctly. It is a distinct possibility. 

One I'll effect that comes to mind is that a partial oil change (the 2 and a bit litres that comes out when the pan is dropped)  disloges (is that spelt right?) crud particles that block a valve or two in the box which causes all matter of gear change problems. Something to think about. 

[eleveneleven]

Interesting about the fuel, I use Shell V power exclusively and it runs/shifts just fine, the only gear I can actually feel once warm is 5th to 6th.

BP is actually the closer station to me but never really considered using their premium stuff, cant see it making any difference but I'll try it on the next fill up...

 

[Malc]

I'm not so sure BP petrol is exclusively BP fuel

Tell you why .....  my local BP station is  run by MFG ....  Motor Fuel Group .... there signs  all over it !  I think maybe they are the ASDA fuel stations too ...  and a lot lot of others .........  maybe I'm too cynical but these days I rarely believe all I see as the " truth "

Malc

[Malc]

https://www.ukfuels.co.uk/new-mfg-sites/

Malc

[Linas.P]

No petrol station in UK runs exclusively their brand fuel. Unless maybe there is petrol station very close to the same brand refinery and it simply makes sense for them to order the fuel from closest refinery. Generally, the petrol stations are franchises and some portion of their fuel comes from that brand to keep the franchise going. The rest is usually supplied by whatever is the closest refinery. 

It seems logical to me that something Shell V Power probably would be type of fuel the stations orders from Shell, because it is not generic, but standard 95 Octane E10 may come from anywhere, as it is just generic fuel.