fuel warning light

[Mickyboy]

Originally Posted by HarryM1BYT

I understood we had established that the handbook was wrong?

That it does not behave that way, that it doesn't come on at a set quantity of fuel. It can be off when I park up, come on as I restart, then go back off again once on the road. In other words - more rapid consumption can bring it on. The actual gauge itself, at lower fuel levels - can rise rise and fall with varying consumption rates.

All of that suggests the gauge display and warning light are based on a calculated range, rather than a quantity of fuel remaining. It is set up so as to deliberately panic the driver, before it runs out. Even if the HiLine system is not installed, the range calculation will still be done and the result available to the rest of the system.

I have tested your first paragraph on lots of 75’s and ZT’s and can confirm that Harry is correct, on the various 75’s and ZT’s this is exactly what happens.
Mick

[HarryM1BYT]

Originally Posted by Al_B

How about using the dash button menu yo get the fuel sender readout? That will tell you how much is in the tank won't it?

The nearer it gets to being empty, the less accurate the sensors become. There are two sensors - floats, each operating a rheostat. The floats can never measure down to the very bottom, because they stop floating an inch or so above the completely empty. Add to that, the fuel will be slopping about in the tank. The two values are measured and integrated in software, to provide a level, then that level is shown by the pointer on the gauge.

When taking the risk of driving a new to me car, with a low tank - I carry a can of spare fuel and keep off risky roads. I have never run the 75 out of fuel.

[T-Cut]

Rather than stopping when the light pops on, it would be interesting to see if the light goes out after a period of low speed driving. The computer apparently calculates range from the data collected over a relatively short period, so by reducing speed/consumption rate, the light should go out after a specific time period. this is because the new range calculation exceeds the proposed threshold. Extrapolating, the light should pop on again if the speed is increased, so reducing the range to below the suggested threshold. It would thus be a reasonably easy way to establish the existence of a range threshold rather than a volume threshold.

TC

[Steve42]

Last week my tank was very low.
Gauge was nearly on 0 and dashboard said I had 3 miles in the tank.
Started the car up and started to de-ice the car.
After a few min it had gone from 3 miles to 10 miles .
I had 10 miles to get home so thought I would risk it .
Drove the 10 miles home and got to the garage.
Stopped and looked at the dashboard I still had 20 miles left in the tank .
Mind you cost me 67 pound to fill up.

[HarryM1BYT]

Originally Posted by Steve42

Last week my tank was very low.
Gauge was nearly on 0 and dashboard said I had 3 miles in the tank.
Started the car up and started to de-ice the car.
After a few min it had gone from 3 miles to 10 miles .
I had 10 miles to get home so thought I would risk it .
Drove the 10 miles home and got to the garage.
Stopped and looked at the dashboard I still had 20 miles left in the tank .
Mind you cost me 67 pound to fill up.

That agrees with my own findings, plus the gauge will also rise and fall a little too, inline with rate of consumption.

[T-Cut]

Originally Posted by HarryM1BYT

the gauge will also rise and fall a little too, inline with rate of consumption.

What possible use is that? I don't understand the logic, if that was MGR's intention. The gauge should fall as fuel's consumed. The rate of fall will vary with the rate of consumption, so why would it be made to rise? I've read several accounts of the varying gauge, but the explanation needs testing. It's just as likely to be a bug in the software.

The wife's car has both a normal gauge plus a permanent range displayed on the dash. I assume the range is calculated as proposed in the thread, but the analogue gauge doesn'r rise and fall in any way. It just falls variably as logic would require.

TC

[HarryM1BYT]

Originally Posted by T-Cut

What possible use is that? I don't understand the logic, if that was MGR's intention. The gauge should fall as fuel's consumed. The rate of fall will vary with the rate of consumption, so why would it be made to rise? I've read several accounts of the varying gauge, but the explanation needs testing. It's just as likely to be a bug in the software.

TC

Sorry, I cannot explain it, it is just what I and others have observed. The only reason for the behaviour I could think of, was one of scaring the driver into to adding fuel and maybe driving in super economy mode until filled.

[T-Cut]

Originally Posted by HarryM1BYT

The only reason for the behaviour I could think of, was one of scaring the driver - - - -

I guess it would balance out the false sense of security that's given by the temperature gauge!

TC

[Steve42]

Originally Posted by Steve42

Last week my tank was very low.
Gauge was nearly on 0 and dashboard said I had 3 miles in the tank.
Started the car up and started to de-ice the car.
After a few min it had gone from 3 miles to 10 miles .
I had 10 miles to get home so thought I would risk it .
Drove the 10 miles home and got to the garage.
Stopped and looked at the dashboard I still had 20 miles left in the tank .
Mind you cost me 67 pound to fill up.

All 3 75s I have had have done the same.
Same as the odd ball idea of the wipers dropping to the next next setting when you stop the car.

[HarryM1BYT]

Originally Posted by Steve42

All 3 75s I have had have done the same.
Same as the odd ball idea of the wipers dropping to the next next setting when you stop the car.

Its not that oddball, I would do that manually anyway, when waiting at the lights.