Fuel low light - game of nerves :-)

DJ Les · March 1, 2019

As a new owner the first few fill ups were around 50 litres when the garage fuel pump cuts off and I was getting less than 300 miles to a tankfull. i read in the manual that the rx400h has a 65 litre tank, so, that meant there must be still 15 litres as a reserve. A quick calculation concluded I should have 88 miles left in the tank after the fuel low light comes on, I was always lead to believe most cars have about 50 miles left in the tank as a reserve.

Thought I would try setting Trip B to zero when my fuel light came on, Trip A was showing how far I travelled on this tank of fuel. This is where it gets to be fun (no petrol can as backup), the first time I got to 27 miles and bottled out. When I filled the tank it took 57 litres......... the next time (this Monday just gone) I got to 54.7 miles from fuel light on and the tank took 58 litres and total of 357 miles from that previous tankfull. Oh btw, this is on standard Esso 95ron octane petrol.

Don't think I'll try to go further without a backup can of petrol, my nerves won't take it lol. But at least I now know I can safely travel 50 miles after the fuel light comes on.

So, has anybody gone further or anyone deliberately ran out with a backup can of petrol to see how far the car will go?

olliesgrandad · March 1, 2019

Definitely wouldn't run out of fuel as there is bound to be a few years worth of crud in the bottom of the tank. I never let the tank go below a quarter. Even that has caught me out. I once owned an Audi A4Quattro where the gauge and computer went faulty without me knowing and I ran out of petrol with 1/4 tank showing...

Hadrian · March 1, 2019

I used to let the tank in my Accord get fairly low, as we didn't use it a great deal. Probably because of this it developed an annoying whine.

So had to source a replacement from a breakers.

m4rkw · March 1, 2019

It's not generally a good idea to let it get low enough to make the fuel light come on. The fuel in the tank cools the fuel pump, if you routinely run it down this low you will likely encounter premature fuel pump failure.

For more info see: http://www.agcoauto.com/content/news/p2_articleid/195

DJ Les · March 1, 2019

Don't intend to run the tank this low in general. But, it was an interesting experiment to see how far I dare go after the fuel low light comes on. I'm now confident that I've got over 50 miles in the tank if I'm in a pinch. Also, I can expect around 300 miles from fuel low light to fuel low light which leaves 15 litres = 3.3 imperial gallons still in the tank. 🙂

Incidentally, I have used http://www.fuelly.com on my Iphone for mpg details etc. for my last few vehicles.

Herbie · March 1, 2019

You should never allow yourself to be "in a pinch" as you say, for all the very good reasons already stated above. It could prove to be a very costly experiment.

When the needle gets to about 1/4 (never less) I fill up. Simples.

DJ Les · March 1, 2019

As stated above I don't intend to run this low normally, this was just an experiment to get an idea of what reserve I've got (in miles).

I intend to fill up when the fuel low light comes on or 300 miles on the trip counter since the last fillup, after all, there's still 3.3 gallons in the tank.

ISJason · March 1, 2019

I always fill up when the gauge shows just under a quarter or a quarter.. the drive system won’t start if there’s no fuel in the tank don’t forget

Sent from my iPad using Tapatalk

BachelorDays · March 1, 2019

For what it's worth, there's never so many miles left in the tank, since it all depends on the type of driving you'll be doing. Beyond that the only real advice is... Don't run out of petrol.

Do, however, note the comments above about the issues running low on a regular basis can cause to the fuel system parts.

DJ Les · March 1, 2019

8 hours ago, DJ Les said:

Don't intend to run the tank this low in general. But, it was an interesting experiment.

7 hours ago, DJ Les said:

As stated above I don't intend to run this low normally, this was just an experiment to get an idea of what reserve I've got (in miles).

BROUWERS · March 1, 2019

I once did well over 100 miles with the fuel light on, but that was on an experimental hypermiling run where I averaged 53.5 mpg (685 miles on one tank). I then managed to get 59.65 litres in there before the pump clicked and turned off 1st time, so in theory I could have gone another 60 miles.

welland · March 3, 2019

On 3/1/2019 at 7:03 PM, BROUWERS said:

on an experimental hypermiling run where I averaged 53.5 mpg (685 miles on one tank).

Crikey, how did you manage that? What sort of roads / conditions / speeds....?

BROUWERS · March 3, 2019

10 hours ago, welland said:

Crikey, how did you manage that? What sort of roads / conditions / speeds....?

Summer temperatures, no highway driving, max tire pressures, minimal luggage on board, no AC, minimal amount of cold starts, pulse and glide where possible, so basically no realistic conditions at all 🙂 Some fair hills on the way though. Calculated actual fuel economy was 51.74 UK mpg.

Delphius1 · March 5, 2019

On My RX300 the low fuel light comes on with around 50 miles range left on the info display. I've run it down past zero miles on the info display by a further 5 miles and still ran the car to a petrol station. Not by choice, but when I was out in the sticks late at night in an unfamiliar area trying to find an open petrol station.

That night I understood what electric vehicle drivers feel regarding range anxiety.. :-)

Rutlandlex · March 5, 2019

Well I've always run the fuel right down until the warning light comes on and even 10's of miles with the warning light on in every car I have ever owned and I have never had an issue. I see filling up with fuel as a necessary evil so in order to reduce the number of fill-ups then I stretch each tank as far as I can.

DanD · March 6, 2019

On 3/1/2019 at 2:11 PM, BachelorDays said:

For what it's worth, there's never so many miles left in the tank, since it all depends on the type of driving you'll be doing. Beyond that the only real advice is... Don't run out of petrol.

Do, however, note the comments above about the issues running low on a regular basis can cause to the fuel system parts.

You're right. Also, you need to consider that the shape of the tank and the position of the outlet pipe will result in some of the petrol not being accessible. The latter will also prevent sediment from being fed into the engine.

I came across the following which might be of interest:
https://carfromjapan.com/article/car-maintenance/everything-drivers-need-know-fuel-tank-capacity/

Mauler · April 10, 2019

On 3/1/2019 at 7:39 AM, olliesgrandad said:

Definitely wouldn't run out of fuel as there is bound to be a few years worth of crud in the bottom of the tank. I never let the tank go below a quarter. Even that has caught me out. I once owned an Audi A4Quattro where the gauge and computer went faulty without me knowing and I ran out of petrol with 1/4 tank showing...

People say this about the inside of fuel tanks, but when my Dad and I removed my old '05 plate TDCi Focus to replace it's fuel sender unit the inside of the tank, which AFAIK was the original and I doubt it had been cleaned in it's then-13/14ish years, was as clean as a whistle.

Ala Larj · April 10, 2019

On 3/6/2019 at 12:39 PM, DanD said:

You're right. Also, you need to consider that the shape of the tank and the position of the outlet pipe will result in some of the petrol not being accessible. The latter will also prevent sediment from being fed into the engine.

I came across the following which might be of interest:
https://carfromjapan.com/article/car-maintenance/everything-drivers-need-know-fuel-tank-capacity/

And I thought the fuel filter was there to prevent sediment entering the engine!

m4rkw · April 14, 2019

On 3/5/2019 at 1:28 PM, Rutlandlex said:

Well I've always run the fuel right down until the warning light comes on and even 10's of miles with the warning light on in every car I have ever owned and I have never had an issue. I see filling up with fuel as a necessary evil so in order to reduce the number of fill-ups then I stretch each tank as far as I can.

You've been lucky, or simply just didn't have the cars for long enough to see the fuel pump go out but this kind of treatment will definitely put significant wear on it. In the same way that a sample of 1 is unrepresentative of many other avenues in life, it doesn't prove anything. There are always people who smoked two packs of cigarettes a day and lived to 90, but extrapolate the trend out over 100,000 people and see what you find 🙂

genkakuzai · April 18, 2019

This has been puzzling me for quite some time, because I've noticed that while it doesn't burn through fuel faster than any of our other two cars, the refill light comes on much much earlier. Today I got "lucky", the light went on pretty much exactly 10 km before I was about to get a full refill. I got pretty much exactly 50 litres in, and since the volume is 65 litres, this would lead me to believe that the refill light comes on when there's around 14 litres remaining.

m4rkw · April 19, 2019

8 hours ago, genkakuzai said:

This has been puzzling me for quite some time, because I've noticed that while it doesn't burn through fuel faster than any of our other two cars, the refill light comes on much much earlier. Today I got "lucky", the light went on pretty much exactly 10 km before I was about to get a full refill. I got pretty much exactly 50 litres in, and since the volume is 65 litres, this would lead me to believe that the refill light comes on when there's around 14 litres remaining.

Does the manual say when it's meant to come on? Assuming you get around 30mpg that would equate to about 90 miles left, which isn't inconceivable I guess but I think they'd likely set the threshold lower. A quick google suggests others see the same so perhaps this is normal.

If so this is a good thing in my opinion - 14L left is still probably enough not to cause damage to the fuel pump so as long as you refill when the light comes on you should be good. If it was half that or lower I wouldn't want to let the light come on.

Zotto · April 19, 2019

When fuel light goes ON I usually refuel ASAP, while instrument gives 50 km. left: actually I have never succeeded to fill more than 58 liters in this situation, so with light on you have at least 7 liters left, that with my usual driving style means 85 km. or more.

Britprius · April 19, 2019

Not withstanding the OP saying he would not run out of fuel purposely. The thing that has not been mentioned so far is that with a hybrid when you run out of fuel it is possible to deplete the traction Battery to a point where it will no longer turn the engine over to start the car. For safety reasons the car will run electric only till the Battery is discharged.
This then means a trailer lift to the dealers for the high voltage Battery to be re-charged. The dealers do not normally keep the special charger in the workshops. it has to be ordered in specially with the operator, and can take some time to arrange at considerable cost.

John.

TimS320 · May 27, 2019

I’ve been having the same thoughts as the OP.

Just in the middle of a holiday across Europe and over 3 full tank fills only managed averges of 320-330 a tank. Only got the last up to 345. The RX handbook states the tank is 65 litres but I’ve not managed to get more than 52 litres in. I always used to assume 1 gallon left when the warning light came on in all previous cars but I am sure this is a lot more. I also can’t get more than 30 mpg on the autobahn, even when trying for an economy run.

However unlike old VWs I don’t run this right down unless absolutely necessary. Only time I had this recently was coming down the A1 from Newcastle to Manchester one night when one services was blocked off for a night closure and the next only had diesel! Pulled in to the third one on fumes, having done 30 miles after it showed zero. Like others, I still couldn’t get near 65 litres, 59 was all. So is there 5 litres of fuel in the tank unused?

On another thought, I’ve been crosschecking the trip computer in the car with two satnavs as we were bored and had a 1000km run to make. When getting an Average Speed indication it is usually 5pmh less than the speedo. The satnav shows in the middle of the two, which is correct as the car speedo should always over read to prevent speeding.

However I wonder if the lower computed averges might have any affect on the really low average MPg I have just got over the last 3 fills of around 28-30mpg.

malcolmw · May 27, 2019

I checked out my 4RX450h for this. I ran it down to zero miles left and then brimmed the tank. Basically, you still have enough fuel for about 45 miles when the range reads zero. The light/warning comes on at about 30 miles range left so you have typically 75 miles to fill up.