1979 245 Coolant Gauge

[Clifford Pope]

A gauge is only measuring an electric current. The first thing to do in any diagnosis is to check whether its information is actually correct. With a temperature gauge you can calibrate it against a proper thermometer.
You can similarly calibrate a fuel gauge by emptying the tank and then pouring in a measured amount of fuel - half a tankful would be a useful check-point.

If both gauges show the same fault then suspect a common fault, and the voltage regulator would be an obvious first stop.

[Clan]

Originally Posted by Clifford Pope

A gauge is only measuring an electric current. The first thing to do in any diagnosis is to check whether its information is actually correct. With a temperature gauge you can calibrate it against a proper thermometer.
You can similarly calibrate a fuel gauge by emptying the tank and then pouring in a measured amount of fuel - half a tankful would be a useful check-point.

If both gauges show the same fault then suspect a common fault, and the voltage regulator would be an obvious first stop.

I would suggest you calibrate a fuel gauge where it really matters that is at the bottom end 😸

However i have found volvo instruments are very high quality and are fairly accurate ..

[Stephen Edwin]

Originally Posted by Clan

I would suggest you calibrate a fuel gauge where it really matters that is at the bottom end 😸

However i have found volvo instruments are very high quality and are fairly accurate ..

My ignorance. At the bottom end?

Thanks in advance.

.

[Clan]

Originally Posted by Stephen Edwin

My ignorance. At the bottom end?

Thanks in advance.

.

yes at the Empty end , that is where we need it accurate .. no where else really matters ... I have found on most volvos that when the needle is exactly in line with the very empty line there is still a useful amount of fuel left ..

[Clifford Pope]

Originally Posted by Clan

I have found on most volvos that when the needle is exactly in line with the very empty line there is still a useful amount of fuel left ..

Are you saying that is a good thing, or are you highlighting the inacuracy?

It depends how you drive.
I like to fill up comfortably in advance of rock-bottom, would ideally like half-full to mean half-full. In practice however the gauge is non-linear in a rather weird way.
It falls from full to 3/4 in no time at all, spends ages in the 3/4 to 1/2 region, falls very rapidly from 1/2 to 1/4, and then hangs about on 1/4 for a long time before suddenly registering in the red.

As a result I take falling to 1/2 as the first warning, and then 1/4 as the "better fill up pretty soon" point.

By contrast the gauge on the LPG tank on my previous 240 was absolutely spot-on all the way down.

[Clan]

Originally Posted by Clifford Pope

Are you saying that is a good thing, or are you highlighting the inacuracy?

It depends how you drive.
I like to fill up comfortably in advance of rock-bottom, would ideally like half-full to mean half-full. In practice however the gauge is non-linear in a rather weird way.
It falls from full to 3/4 in no time at all, spends ages in the 3/4 to 1/2 region, falls very rapidly from 1/2 to 1/4, and then hangs about on 1/4 for a long time before suddenly registering in the red.

As a result I take falling to 1/2 as the first warning, and then 1/4 as the "better fill up pretty soon" point.

By contrast the gauge on the LPG tank on my previous 240 was absolutely spot-on all the way down.

I have done a great deal of driving in all the models with low fuel levels over many years ,and one thing is consistent , you don't run out of fuel whilst the needle is exactly on the empty line .. you have enough to get to the nearest fuel station at least . which is how it should be ...as no one lets the needle get to Empty before they think about re fuelling

with your 1/4 tank level you probably still have enough fuel for around at least 150 miles i would think depending on whether you average 35 or 45 mpg . so no need to worry about refuelling at 1/4 tank 🎅

[Clan]

Originally Posted by Clifford Pope

Are you saying that is a good thing, or are you highlighting the inacuracy?

It depends how you drive.
I like to fill up comfortably in advance of rock-bottom, would ideally like half-full to mean half-full. In practice however the gauge is non-linear in a rather weird way.
It falls from full to 3/4 in no time at all, spends ages in the 3/4 to 1/2 region, falls very rapidly from 1/2 to 1/4, and then hangs about on 1/4 for a long time before suddenly registering in the red.

As a result I take falling to 1/2 as the first warning, and then 1/4 as the "better fill up pretty soon" point.

By contrast the gauge on the LPG tank on my previous 240 was absolutely spot-on all the way down.

I have done a great deal of driving in all the models with low fuel levels over many years ,and one thing is consistent , you don't run out of fuel whilst the needle is exactly on the empty line .. you have enough to get to the nearest fuel station at least . which is how it should be ...as no one lets the needle get to Empty before they think about re fuelling

with your 1/4 tank level you probably still have enough fuel for around at least 150 miles i would think depending on whether you average 35 or 45 mpg . so no need to worry about refuelling at 1/4 tank 🎅

Have you got one of the late cars with a bar graph gauge ? If so , Did you know that the lowest segment goes orange when low then turns to red when you still have about a gallon left .. The new cars have a large diameter tank but not very tall so it does have some mathematical inputs to the gauge , this was going on 24 years ago in the S40 and V40 ranges .