Petrol Gauges

[andyd]

No big deal, but just realised the Mk2 gauge has evenly spaced markings, but the Mk3 appears to be unequal, ie the halfway/middle mark is actually closer to the 3/4 than the 1/4.

So if we have 58 litre tank capacity the half mark is actually more than 29.5 litres and well over 30 litres imo.

Mk2 https://www.rallyspares.com/ford-new-ol ... gauge.html

Mk3 https://www.google.co.uk/search?biw=153 ... aZAyk3vcwM:

[stevemarl]

Funnily enough I actually checked exactly this today! Mine (`84) was on 1/2 mark today and I filled it to brim, 29.1 litres or 6.4 gall which is exactly half the 12.75gallon tank. I think Martin, Caprigear, once said that the Mk2s and maybe early 3s, had a different (front mounted?) sender which maybe swept through a different arc & therefore would give a different centre reading? Maybe Mk3`s sender`s not as linear - but reads correctly with the appropriate gauge if you see what I mean?
* I`m afraid I`m of an age where litres get converted to gallons as I understand what 40mpg means

[Andrew 2.8i]

I reckon that if we all tried to duplicate Steve's observations, we'd all get different results about how much fuel is left when the gauge indicates half full.

Good spot about the gauge, I hadn't noticed that before. The half way mark on the mark 3 gauge looks like it's half way up the usable part of the gauge. What I mean by that is that it is halfway between full and the top of the red section.

Andrew.

[andyd]

Funnily enough I actually checked exactly this today! Mine (`84) was on 1/2 mark today and I filled it to brim, 29.1 litres or 6.4 gall which is exactly half the 12.75gallon tank. I think Martin, Caprigear, once said that the Mk2s and maybe early 3s, had a different (front mounted?) sender which maybe swept through a different arc & therefore would give a different centre reading? Maybe Mk3`s sender`s not as linear - but reads correctly with the appropriate gauge if you see what I mean?
* I`m afraid I`m of an age where litres get converted to gallons as I understand what 40mpg means

Steve,
Gallons, miles, feet and inches etc.
But as the petrol pumps are now in litres it's easier to talk that here

Got a feeling my gauge is at fault.
When I got the car the needle would often drop off the scale when it was just over or around 1/4 tank, so put new tank and sender on.

When I last used the car the needle was a little under 1/2 when I put it in the garage, so I assumed around 25 litres left towards my next trip.
Got in it Sunday and within half a mile it was down to 1/4, and barely changed on hills. Got to the petrol station and put £30 (24 litres in which it took easily) so I was expecting it to read 1/2 to 3/4. Wrong, it went right off the top of the gauge which in theory meant there was about 34 litres in it when it was reading 1/4

Did around 40 miles and when I got home it was reading just under 3/4.

I think brimming the tank from now on and doing say 200 miles then fill again. I have put a gallon can in the boot incase I get caught out

[Andy76]

It may be worth checking the compatibility of the gauge and the sender. I've just sold my 2.8 but when I bought it the seller said it had a new sender. It was reading way off. When I investigated the resistance range of the sender was wrong. I had to buy a new one (from retro ford IIRC). It wasn't cheap!

Unfortunately I can't remember the resistance range that the gauge is calibrated to. You can check by connecting a variable resistor to the gauge wiring where it connects to sender and seeing what resistance gives empty and full. I suspect mine had been fitted with a Sierra sender which operates at a different resistance. You will need to remove the sender and check what its operating resistances are using a multimeter.

Andy

[andyd]

It may be worth checking the compatibility of the gauge and the sender. I've just sold my 2.8 but when I bought it the seller said it had a new sender. It was reading way off. When I investigated the resistance range of the sender was wrong. I had to buy a new one (from retro ford IIRC). It wasn't cheap!

Unfortunately I can't remember the resistance range that the gauge is calibrated to. You can check by connecting a variable resistor to the gauge wiring where it connects to sender and seeing what resistance gives empty and full. I suspect mine had been fitted with a Sierra sender which operates at a different resistance. You will need to remove the sender and check what its operating resistances are using a multimeter.

Andy

Hi Andy,
I got the sender from Caprigear so I know it is the correct one.

[Jasonmarie]

So to get this right are we saying that half a tank is not half but 3/4 full ?

[stevemarl]

The problem is that the variable resistance is achieved by having a long piece of resistance wire wound round and round an insulating former, so it forms a sort of closely packed flat coil spring: the blade of the moving arm moves along the edge of this `coil` thus varying the effective length of wire in the circuit & hence resiatance. Problem is, over time and usage, the wires can become bunched up, maybe even touching so shorting out - this will give an area with a very large change in R for a short travel. Between the bunching they become spread out which will mean a large travel with little change in resistance. Just means the output is not as linear as it should be. Unless you were to partially dimantle the cover it`s impossible to tell what`s what. I think the only thing you can do is try to read how your particular gauge works - which is why I brimmed mine today, just to check.. I`m sure mine drops off rapidly in the lower 1/4 and I suspect there`s much more left than it says (that`s for another day ) You could get another sender and it could be the same. It`s not one of the new batch that a CapriPower member had manufactured is it?

[Mc Tool]

Mine is like andyd's ......sorta . I have never seen the gauge read full and on the "run till dry" test , once the needle has dropped down thru the red zone I got another 100 miles before it ran dry might fix it one day .... probly not, got used to it now and plus the Mrs hates it , firkin funny really , picture some OCD woman at the fuel depot .........wantin a tank full ......no matter what she does ...... and its worse with her in the passenger seat while I drive round for 3 days in the red , but she cooks well

[andyd]

When the old sender unit was removed you could see damage to part of the resistance wires.

The new sender unit from Martin was fitted in April and it's only done a couple of hundred miles so that must be ok.

[andyd]

So to get this right are we saying that half a tank is not half but 3/4 full ?

It looks like the gauge marks are correct, although the 1/2 mark just looks slightly higher. As Steve says, probably how the sender is set to read.

The last time I brimmed a Capri was my 280, only to find some leaked back out the tank from somewhere underneath

[tejb1]

My sender gives very little movement in the 3/4 to 4/4 area, then moves much faster between 1/4 and 3/4. I'm paranoid though - the tank is normally full and in any case almost never goes under half a tank!

[T.M.]

Here is some early Mk3. Looks it has marks on gauge in same way as Mk2.

https://img2.auto.cz/img/29/full/4701487_.jpg
https://img2.auto.cz/img/29/full/4701488_.jpg

Tom

[andyd]

Here is some early Mk3. Looks it has marks on gauge in same way as Mk2.

https://img2.auto.cz/img/29/full/4701487_.jpg
https://img2.auto.cz/img/29/full/4701488_.jpg

Tom

Tom, the halfway mark is halfway up the gauge.

[T.M.]

Yep.