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Trip Computer And Reserve Tank


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I have only recently purchased my car and I filled up the other day when the trip said 10 miles left but I only got 56 litres in the tank so there was still 2 gallons left.

Can anyone confirm that the trip computer ignores the reserve or is it an issue with my trip ?

Thanks

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I have only recently purchased my car and I filled up the other day when the trip said 10 miles left but I only got 56 litres in the tank so there was still 2 gallons left.

Can anyone confirm that the trip computer ignores the reserve or is it an issue with my trip ?

Thanks

The mpg figures shown by the OBC on my GS430 tend to be almost identical to the figures that I get manually (I always brimfill), but the "remaining miles" is always out. Easy to check the approximate "true" fuel remaining though if you know the size of your tank.

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I appreciate I can check the true fuel by what I get in the tank at fill up but just wanted to check that the trip ignores the reserve.

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From my experience, it does NOT ignore the reserve. Usually when my goes into reserve, I normally have around 35 miles remaining.

Interesting, when I last filled up the needle was on the "R" and I got 56 litres in the tank which indicated that there was still 9 litres remaining but my trip is showing 0-10 miles left in the tank.

On my previous Audi the trip would show zero miles left but you could still get about 20-30 out of it.

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I appreciate I can check the true fuel by what I get in the tank at fill up but just wanted to check that the trip ignores the reserve.

As far as I am aware, Lexus do not have a "reserve" fuel tank as such. It may be that the OBC is set to ignore a certain amount of remaining fuel because the indicated remaining miles can fluctuate by maybe 10 miles even if you cover only 2 miles.

Since the Lexus OBC seems pretty accurate regarding mpg the point I was making was that you can easily tell how much fuel is left at any given time before you fill up.

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If you let it go that low there is small chances you will get air locks in the tank and not get enough in. But my IS220d ran once at "0" miles left for 15 miles before I got to a station in Scotland hills, and it took 60 litres dead.

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this has been on my mind since i bought my IS. as far as know the IS250 tank 65litres, however, when i fill up the tank with about 30 miles left (according to the trip) the tank fills up with only 55-57 litres. so it hides 10litres somewhere. my theory is that the IS keeps the other 10 as emergency to make sure you always keep the tank filled and not let it run dry.

to b honest in a way it better for me since instead of filling every week with £65 i only need £55. :D

just to check can every one who is reading this topic please check the next time they fill up how many litres you get in to fill up tank. also please note how many miles you have left acc. to trip. thank you.

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When my OBC gives me a range reading of 0 miles there is somewhere between 1 and 2 gallons still in the tank, so it's obviously being overly cautious and trying to disuade us from running the tank right down - which is fair enough.

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I always tend to fill up when i get down to a quarter full anyway so i don't worry about how accurate the last bit of the fuel gauge is. I know exactly what fuel consumption I'm getting because I always brim it and record the amount of fuel going in, and then zero the trip meter.

I expect most manufacturers make the gauge pessimistic so you don't run out unexpectedly through not paying attention to the gauge.

Even if you did know that when the OBC says the range left is 0, that there's still a couple of gallons left, would you really drive 30 or 40 miles happily?

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I always tend to fill up when i get down to a quarter full anyway so i don't worry about how accurate the last bit of the fuel gauge is. I know exactly what fuel consumption I'm getting because I always brim it and record the amount of fuel going in, and then zero the trip meter.

I expect most manufacturers make the gauge pessimistic so you don't run out unexpectedly through not paying attention to the gauge.

Even if you did know that when the OBC says the range left is 0, that there's still a couple of gallons left, would you really drive 30 or 40 miles happily?

No I would not but right now my trip is saying 3 miles left but my local Shell garage near home is 4p per litre cheaper than the one near my work so I wanted to make sure I can do the 7 mile journey without running out of fuel.

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Buy 2 litres (minimum sale) near work to get you home, then fill up at Shell.

You have "lost" 8p but will get home comfortably.

I can't believe we are discussing this.

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Buy 2 litres (minimum sale) near work to get you home, then fill up at Shell.

You have "lost" 8p but will get home comfortably.

I can't believe we are discussing this.

I couldn't agree more. If you are worrying about how much the fuel costs then you shouldn't be in the car in the first place. Just fill the thing up and enjoy the car. Unless you've got the diesel of course.

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Buy 2 litres (minimum sale) near work to get you home, then fill up at Shell.

You have "lost" 8p but will get home comfortably.

I can't believe we are discussing this.

I couldn't agree more. If you are worrying about how much the fuel costs then you shouldn't be in the car in the first place. Just fill the thing up and enjoy the car. Unless you've got the diesel of course.

If you read the original post the question was about the trip computer vs the actual fuel left, I was trying to establish the accuracy and wanted to see if other owners could help.

I could not care less about the 8p but the nearest garage to my work takes me in the wrong direction and I would have to sit in rush hour traffic for around 20 minutes to get there. My journey home is only 25 minutes.

As said originally I have only recently purchased the car and am trying to get an idea of the accuarate MPG.

For those of you who are interested my trip said 0 miles for about 3 miles of my journey and when I filled up I got 60 litres in.

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"As said originally I have only recently purchased the car and am trying to get an idea of the accuarate MPG."

With respect, using the range figure is not the way to do it.

The first answer from dave1 says it all really.

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this has been on my mind since i bought my IS. as far as know the IS250 tank 65litres, however, when i fill up the tank with about 30 miles left (according to the trip) the tank fills up with only 55-57 litres. so it hides 10litres somewhere. my theory is that the IS keeps the other 10 as emergency to make sure you always keep the tank filled and not let it run dry.

to b honest in a way it better for me since instead of filling every week with £65 i only need £55. :D

just to check can every one who is reading this topic please check the next time they fill up how many litres you get in to fill up tank. also please note how many miles you have left acc. to trip. thank you.

Lucky me just filled up

i had 23 miles remaining and the Tank has just taken 57.83L at £1.00.9 per L (what ever happened to the 14p gap between petrol n Diesel)

then gave me a range of 508 miles then i drove very good at 30mph & 40 and i was showing Tank ave 44.5MPG and overall i am showing

40.7 MPG

if any mathamaticians want to work that out see if it is reading true

IS220d

Matt

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Buy 2 litres (minimum sale) near work to get you home, then fill up at Shell.

You have "lost" 8p but will get home comfortably.

I can't believe we are discussing this.

I couldn't agree more. If you are worrying about how much the fuel costs then you shouldn't be in the car in the first place. Just fill the thing up and enjoy the car. Unless you've got the diesel of course.

Oi not Every Diesel is S :tsktsk: T And i bet yer happy now your petrol is the same price as Diesel (unless your company pays for it)

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Remember Jeremy Clarkson when he drove the A8 from North London to Edinburgh and back. He was on "0 left" for ages before he got the cough from the engine, only 100 yards from the North London pumps.

So I think it is normal, all cars have a 2 gallon or so reserve.

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  • 3 months later...

Just the other day I thought about how much I get out of a tank with the IS250. So today i went to fill up with the trip computer saying 15 km (about 10 miles) left to drive. Without squeezing in anything extra, I filled it up with 57.59 litres. Knowing the reported tank size is really 65 litres, I would say the reserve is about 7 litres, which we don't even normally use because the trip computer would show 0 to go...

I understand you shouldn't drive the tank to totally empty, but I'm just used to the empty tank light turning on when the last reserve is indeed in use (50-100 km left), but with Lexus there seems to be a double safety net then... This would also mean that the range when used according to the trip computer is about 50-100 shorter than it could be.

With my previous cars the light showing up would mean the reserve was in use, and the 0 coming up mean't the tank was totally empty, so this is something of news to me.

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