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6th gear use on Motorway (is220d)?


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Hi all, 

About half of my driving is on motorways where I'll be averaging 125kph / 77 mph.  I assumed that 6th was better for this type of driving both in terms of MPG and also not loading the engine, but from what I'm reading I'm wondering is this the case? I'm reading some conflicting stuff about both MPG and also Carbon build up in the engines. 

I can do a test with it; clear out my average MPG and drive 1 day in 5th and 1 day in 6th to check the MPG, but am wondering more about the engine / carbon side of it.

Do people feel you'd be better off in 5th or 6th for a run like this? What measurements / tests / experience have you?

Curious G :) 

 

 

 

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Hi Graham,

I have tested this quiet a few times  now it really comes down a few things,

  • Distance
  • Type of fuel

I have a 2010 Is200d so may differ from you however I always use Shell Regular diesel I  did a trip to London- Bradford during xmas time where  I used 6th gear 70mph -80mph and I averaged around 52mpg, this kind of dropped on my return journey  due to start/stop traffic.

I normally use M1  for daily commute for around 10-15 miles either way, and can average around 40mpg with 15 miles dual carriway and town roads, however the other week i filled up the tank with Shell Fuel Save, and mpg dropped  down to 38mpg, so i just keep driving in 5th gear  and mpg dropped down 35mpg, then switched back to Shell Regular Diesel it went back up to 40 Mpg.

I tend to drive in 5th gear at 70 mph when joining the mway or around dual carriage  to give the dpf a clear out and get some extra power, i dont really see the soot coming out maybe its just hard to tell from the mirrors.

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Hi there.

I do a fair few miles on the M25 and M4, and what I have discovered so far is that 5th and 6th on the IS are terrible for UK motorways :smile:

I tend to either do 60mph in 5th or 80mph in 6th.  I don't like to hang around between those speeds really since neither gear seems to suit.  Although I suppose 77mph is close enough that I would use 6th.

What I have learnt is that going around 80-85mph as apposed to 60-65mpg loses me roughly 5mpg.  Between a mix of town and motorway driving, I am currently managing about 38mpg.  Last few trips I was in more of a hurry, so with the higher motorway speeds, it dropped to 33mpg.

As for the carbon build up, to keep your EGR value and DFP clean, it is recommended that you do at least 15 minutes driving at a constant 1800-2000rpm.  Since this corresponds to the speeds I do, I tend to manage more than 15 minutes at that RPM :smile:

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Hi All 

I swapped my 220D for a 250 for multiple reasons however one of the main ones was the very poor gearing in the 6 speed gearbox. I always found that it was pointless trying to get into 6th unless you were going 80+ anything below that caused the engine to sound like it was struggling and caused some vibrations throughout the car. I always found that sticking in 5th gear produced better results in regards to the MPG. 

With a mixture of motorway and town driving I only even achieved an average of 40-45 MPG from the 220D over a tank. I'm now happily getting 30-35 MPG from my 250 with no gearing problems at all (best choice I ever made).

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Thanks for the replies. I've only been driving this car for a few weeks and about 80%+ of my driving is motorway so going to play a little and see if I can inch up the MPG. 

I've started a bit of a test to see what happens at the moment - as info EGR been recently cleaned, car serviced too, no A/C on, and using regular diesel nothing too fancy. My starting measurements from this morning, I spent 20 mins on the motorway doing a steady 75MPH:

- first 10 mins in 5th gear; averaged 6.9L/100KM (41MPG); the car felt fine but was revving at about 2000-2300 revs 

- last 10 mins in 6th gear; averaged 6.4L/100KM (44MPG). During this time I was sitting at about 1600-1800 revs. It was OK, no obvious vibration but I felt I was really at the bottom end of the limit speed wise for this gear.

But from this first run it looks like at this speed 6th gear is a little more efficient. What I plan to do is repeat this test and then start to play a little more to vary the speed, gears. Also I've ordered some fuel additive which people recommended (AR6400-D) so I'll start to add this and see what happens. Also need to check my tyre pressure, I think it's OK as was recently serviced but will double check.  

So in case anyone is interested in my NERD experiment, stay tuned :) 

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I had a 220d a few years back. I was fortunate as mine gave good mpg.

I found i could only use 6th when doing 80+ mph (usually when I was driving in France) At lower speeds the engine was labouring a bit and drone was an issue inside the cabin.

5th was best for me on a journey doing around 70-75mph. If I recall correctly, we drove back from Scotland to Bournemouth in one day and averaged close to 54mpg.  My work run would give about 35mpg and other gadding about produced 44mpg. 

I did use AR6200 at fill ups and put a can of BG244 through the tank every 6-8000 miles. I also checked and cleaned the EGR regularly.

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I dont get why people say 6th is unusable at motorway speeds. I use mine in 6th at 63mph, and average around 53-55 mpg. 

 

True, you need to change down to overtake, but for cruising with the cruise control on, it works beautifully.

5th gives around 47-50 mpg at that speed.

I only use 5th when driving 50 at motorway roadworks, it gives me good 60 mpg then.

 

My MPG may differ from others though, as I drive north-south every week, so going through half the country I get a good set of motorway bits with inclines and declines that create a realistic average.

Some people may only have an incline to drive up, so their mpg will be a lot worse.

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Those are some impressive mpg figures you have there.

However, in my experience, at anything less that 75mph, the car really struggles in 6th, even to maintain the speed.  Tried it last night and it required lots of throttle and took an age to gain the speed back if I dropped to even 70mph.

So at 63mph, even an incline on cruise control would make mine seriously struggle to pull the car along.

Still, if it works for you, then great.  I wish mine were the same. :smile:

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20 hours ago, chris_abr said:

I dont get why people say 6th is unusable at motorway speeds. I use mine in 6th at 63mph, and average around 53-55 mpg. 

 

True, you need to change down to overtake, but for cruising with the cruise control on, it works beautifully.

5th gives around 47-50 mpg at that speed.

I only use 5th when driving 50 at motorway roadworks, it gives me good 60 mpg then.

 

My MPG may differ from others though, as I drive north-south every week, so going through half the country I get a good set of motorway bits with inclines and declines that create a realistic average.

Some people may only have an incline to drive up, so their mpg will be a lot worse.

When do you allow your turbo to kick in?

I couldn't drive 63mph on the mway it jus to slow for me, need to be going 70+

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On 1/28/2016 at 9:17 PM, jayt13 said:

When do you allow your turbo to kick in?

I couldn't drive 63mph on the mway it jus to slow for me, need to be going 70+

I don't. 

Once turbo kicks in you get bad fuel economy.

If you keep it around 63-65 mph gps speed, you should get around that 50-55 mpg from it.

Once you go above 70 (tested at 73 gps speed / 75 acc. to speedo, cruise control on a 180 mile journey), you're talking about 45 mpg.

 

I did another test yesterday, 180 miles on m5/m6, with 58gps/ 60 speedo  as average speed (speed up every now and then to overtake), and my MPG was at 62 on that journey.

 

I've also noticed that my indicated mpg worsened with 17' instead of 16' as I had previously.

But that's due to the fact that the 17'' is roughly 3cm bigger in total resultant diameter of the wheel, and the ECU thinks it's going slower than is actually is, and the mpg calc is skewed to show worse result.

Once I calculated the real MPG I got that day after driving to range of zero, then getting a full tanks fuel (it took 59.5 litres, so only 2.5l were remaining in the tank when it showed zero miles), the ECU had my trip as 610 miles when in reality my mileage was over 680 (took a distance measurement from satnav), so it gave me 47 mpg average when it reality it was over 51.5. And that includes about 1/4 city driving. So not too bad for mixed driving result.

 

As you can tell, I take my mpg measurement way too seriously haha, but it'd be interesting to see if someone else did a measurement like mine, and compare the scores. My car's got 200k miles on the clock, so the engine surely isn't as efficient as it used to be, so I wouldn't be surprised if other people got even better results in brim to brim testing.

 

 

But going back to the main question - you want fuel economy, stick to 6th and change down to overtake, if you want the convenience of not having to change down every now and then, just accept the lower mpg.

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On 25/01/2016 at 6:00 PM, Shahpor said:

I do a fair few miles on the M25 and M4, and what I have discovered so far is that 5th and 6th on the IS are terrible for UK motorways :smile:

 

This actually makes sense and is completely correct, because in majority of Europe and Japan the speed allowed is 130 km/h or 81 mph. So when driving 70 mph you are really reaching the speed for 6th (overdrive) gear. Similarly, in US (the major market) the majority of the roads are limited ~60 mph and historically were limited at 55/65mph (until 1995). Even currently there are just certain extra urban "freeways" where you can drive up to 85 mph, but is not like common. So tactically the gear ratios are correct for Lexus major markets EU/Japan -6th, US -5th. It is only UK (sadly) where the majority of the motorways(and other roads) are limited to 70 mph. I personally, believe this is more of the UK issue than Lexus - theres is no real reason why speed limit cannot be lifted to say 90 mph - but that is different topic. True - Lexus could adapt gear rations to UK, but they didn't (probably because it is minor market). Actually, I am quite happy they didn't as most of the time I am .... (well you know what) :).

On 31/01/2016 at 8:45 PM, chris_abr said:

But that's due to the fact that the 17'' is roughly 3cm bigger in total resultant diameter of the wheel,

Not only the 17 inch are bigger, but I guess the tires are wider (should be wider). And the tires are actually bigger contributor to fuel economy, wider tires are obviously grippier and hence have larger rolling resistance. The rim size would matter more in acceleration, and would unlikely to contribute to fuel consumption while driving at steady speed on motorway. Depending on the speed and rpm of the engine bigger rims might even have better fuel economy (if not the tires).

On 31/01/2016 at 8:45 PM, chris_abr said:

Once turbo kicks in you get bad fuel economy.

Other important thing I would like to note - yes turbo probably affects the fuel economy (didn't have IS220d long enough to have opinion on that), but it actually makes the fuel to burn more efficiently. Essentially, what I am trying to say - driving the diesel car on RPM which is below Turbo range will impact the reliability, not only you are risking to block DPF, but as well turbo itself. So it is better for a car and for the engine to actually be in the turbo range.

Finally, this is really cost vs. benefit. If you drive relatively low miles (under 25k/a) then you better off staying in turbo range - the fuel saved will not cover maintenance costs. If you doing a lot of miles (e.g. company car, which is unlikely to be Lexus IS) then maybe it is actually worth to save money stis way - yes after 60k miles you will have to replace DPF and the Turbine (and maybe other pieces ... like the whole engine :D), but the fuel saving will work out better than maintenance. Though, I am unsure if that saves money (unless you sell the car just before breakdown), here are my calculations:

12000 annual (that is about average for private cars):

  • at 45MPG it will cost you: £1188
  • at 55MPG it will cost you: £962
  • worse case scenario - you will have to replace turbo after 5 years (£1500-3000) and DPF (maybe twice £1200) ~£3500+
  • you're saving on fuel 5 years £1132

Obviously, you can have best of both - if you do maybe one day driving in 5th to flush the turbo and partially DPF, then you can still save money.

Note: Above calculation is just part of the whole story. I am sure there are many permutations I didn't consider here and it is very complex matter. E.g. you might crash the car in 5 years or sell it, finally DPF are getting blocked anyway and even driving perfectly (in terms for DPF) you will still need to replace it sooner or later.

Personally, I did all these calculations and therefore I have IS250 (and generally petrol cars). It makes sense for the high mileage company car to have diesel (which does maybe 60k annual), but not for personal use. You are better of if you can drive it on motorway, but especially in the city is more of the trouble than benefit. Furthermore, used diesel cars are bad investment, because they are likely have covered many miles and have DPF and Turbo partially blocked. To conclude any saving on fuel on diesel cars are contributing to spending on the maintenance, hence it only makes sense where you saving is greater than spending, and for diesel cars there are only few specific cases where it is the case.

 

 

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That is some post Linas :smile:

While you are quite right about the motorway speed thing, can I politely comment that I think your conclusions about turbo economy are wrong.  Let me explain why.

Firstly, what Chris says about turbo boost effecting fuel consumption is not totally correct.  You are right in saying that the boost increases fuel saving, and it does burn the fuel more efficiently.  However, it is not the boost that effects economy, but how much fuel is entering the engine due to the accelerator being pressed.  After all, when on the motorway, you can be in turbo boost range (above 1600-1800ish RPM), but without any throttle input, the turbo wastegate is wide open, so the turbo will not be spinning very fast.  The reason this is not a problem on the motorway is that, once you do put your foot on the accelerator again, there is enough air flow coming into the inlet that the turbo has no trouble spinning up again.

This is also why driving below boost range is so inefficient;  effectively you are driving a turbo car without a turbo and the car struggles from lack of power, thus requiring more fuel to pull itself along.

So you see that ideally, you always want to be in turbo range, regardless of what kind of mileage you do.

Secondly, there is no reason why you would need to replace the turbo and DPF after 60k miles.  Yes, doing short town trips will eventually clog the DPF, but a quick blast up the motorway once in a while will solve that problem.

Also, the turbo is not effected by the type of driving you do at all.  Since the turbo is located before the intake on the inlet track, it doesn't suffer any carbon build up.  Equally, since the exhaust gases are so hot and the turbo spins so fast, carbon build up on the exhaust turbine is also relatively uncommon.  What kills turbo's is the oil seals around the centre shaft wear out and start leaking.  This means that either the shaft starts wearing or oil seeps into the inlet or exhaust.  Most modern turbo's last more than 5 years, for example, mine, as far as I know, is on 115,000 miles and 8 years so far (touch wood).

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19 minutes ago, Shahpor said:

So you see that ideally, you always want to be in turbo range, regardless of what kind of mileage you do.

Sorry for long log response, but the above was what I was actually trying to say.

My point - trying to deliberately be below turbo range, to save the fuel will cause issues.

Point 2 - depends what you mean "once in awhile" - if that is like 1 day from 5. Then yes. If DPF is already fully clogged, nothing but replacement will help.

I never said you need to replace turbo every 5 years - surely they can do and will do more than that if you let them spin. Driving below turbo range will clog DPF which is actually in most cases located just after turbo exhaust outlet (that is because it needs high temperatures to burn the residues of diesel particles). That means that after DPF is clogged the Turbo exhaust outlet will soon be blocked as well. I have personally seen the turbos which are clogged to the level where they no longer spins - this is because blocked DPF creates "negative pressure" (not sure is that is correct term, but I hope you get what I mean) and basically start pumping all crap back to the engine.

So the conclusion - let your turbo spin, say in turbo range and you will have no problems with turbo not DPF.

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No need to apologise, there is nothing wrong with long posts :smile:

Yep, you are correct when you say staying below turbo boost range will not save fuel.

Well, according to the Lexus tech I spoke with, generally a blast once a month would be sufficient.  He said that because the clogging in cumulative, and good blast for about 20 minutes at 1800rpm or above will get the DPF to the 640C required to burn off the carbon.  Obviously, the longer you do it, the better it would be for the cleaning process. 

Sorry, I must of misunderstood, but you said 

1 hour ago, Linas.P said:

If you doing a lot of miles (e.g. company car, which is unlikely to be Lexus IS) then maybe it is actually worth to save money stis way - yes after 60k miles you will have to replace DPF and the Turbine (and maybe other pieces ... like the whole engine :D), but the fuel saving will work out better than maintenance.

and since you said 12,000 miles a year, that equates to 5 years.

Anyway, I think we can agree that getting the car boosting is a good thing for both economy and the clogging issue :smile:

 

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You are right, this is not very clear- I guess that is the problem with long posts. - Will edit it to make more sense there.

I guess it depends how much you drive - if not much maybe once a month for 15 min will be enough.

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I have to backtrack on what I said. Yes, staying in 6th and around 1300rpm gives you ridiculously good mpg (best I got was 65mpg average on 180 mile journey).

 

but after doing only two journeys like that, each 180 miles, my dpf clogged up ( P2002 code) 

Car went into limp mode, couldnt do much with it.

 

I did eventually fix it up the next day - drove at 3.5k rpm at 50 mph for good 20 mins, it was a nightmare. Barely drove 2 mins after starting the engine, and it would go into limp mode again. Then had to pull up on the hard shoulder, restart the car - had another 2 mins "allowance". After about 10 pull ups, the car eventually stopped going into limp mode, so I could properly thrash it. Averaged 21 mpg on a 40 mile motorway journey!

After half an hour, and about 100 ****** off drivers who now have to clean their cars from my exhaust smoke (😂), the DPF was clean enough and the car drives properly again.

Seems to have more power too actually.

 

So as you say, the conclusion is, you can get the good fuel economy by driving the 60mph in 6th, get 65mpg, but always remember to then drive at 75 mph in 5th, so the DPF gets cleaned up, you'll get around 48 mpg on that trip, but when you average it all out, its still a respectable 56.5 mpg average at 67.5mph average if you alternate between the driving styles.

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By the way, now that we have working ECU modding on the 220D, I'd recommend you disable the EGR valve. That's that main issue behind all the problems with 220D - head gasket failures, turbo failures, DPF failures.

Everything gets clogged up with the carbon deposits, and EGR doesn't actually reduce the emissions that much either.

Once you disable it you'll get slightly better fuel economy, and it'll stop that annoying cleckoty noise you get from the engine whenever you have the throttle partially pressed (Noise is just the EGR doing its thing).

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22 hours ago, chris_abr said:

I have to backtrack on what I said. Yes, staying in 6th and around 1300rpm gives you ridiculously good mpg (best I got was 65mpg average on 180 mile journey).

but after doing only two journeys like that, each 180 miles, my dpf clogged up ( P2002 code) 

Car went into limp mode, couldnt do much with it.

That is the best example of what I meant :D - thanks for sharing.

The funny thing, there are many people who actually only drive their cars like that. And make conclusions - "DPF is crap"! so they "delete" it and continue driving this way. This is because some older cars allowed this driving "style" before DPF were invented (or enforced), hence creating "super economical diesel myth". Then you can clearly see who they are, when they pull from junction and leaves everyone in thick black smoke. It is true that it makes good MPG this way, but is so terribly smoking and polluting environment. 

 

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