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MG Midget and Sprite Technical - Fuel Gauge

Hi Guys

As you know, I own a 1975 midget.

Is there any way of checking the accuracy of the fuel gauge.

Currently it is showing just over a quarter full, would his be accurate or not?

Rylan
R Williams

Rylan,
In general these old gauges can vary a lot. You also dont know if a PO has changed either the sender or the gauge or both in the past and they may not be compatible. I have seen cars showing 1/4 full when it has run out and equally others showing empty with a couple of gallons in the tank. Only one sure way to find out. Put a gallon in a can and leave in the boot and then run it until it runs out.

Trev
T Mason

Mine reads backwards (shows full when empty and quarter full when full). Explain that!
Chris H (1970 Midget 1275)

Short of pulling the tank off (not particularly tricky, unless the nuts are seized) then there's no easy way of getting to the sender. If you look in the manual (original owners manual or Haynes) then that will tell you the capacity of the tank. Go to the petrol station & take a note of how much fuel fits in before it goes 'clunk'. Then do the maths & find out how accurate your gauge was!
I always carry a 5L tank in the back, got me out of trouble once when trying to get the tank empty for removing it!
-Craig
C Robertson

Chris H,
Reverse the two wires on the back of the gauge and maybe it will read the right way round.
Mike Howlett

I recommend calibrating your gauge using these instructions:

http://www.mgb-stuff.org.uk/electricstext1.htm#adjust

My gauge only ever goes up to 7/8 full, but more importantly at the bottom end it reads correctly. On 'Empty' I have about 5L left in the tank.
TonyJH

Rylan
- accept the gauge as an approximation as long as it's near to being accurate when the tank is towards being completely empty of full - recalibrate the gauge if not

As Trev points out there could be a lot of variables, if you're going to run until you completely run out then I suggest a fuel filter just before the carbs to catch possible rubbish at the bottom of the tank

Craig's idea will work but wont be very accurate because of unknown variables and its inaccuracy may be opposite to the generally acceptable inaccaracy of the fuel gauge or it might compliment it

I think all fuel gauges vary in their accuracy over their range from E to F

You might think this next bit is trite but if you think about it it makes sense - you'll learn how accurate the gauge is over its range the more the use the car and get used to it

Carry a full can in the boot, have a fuel filter

My new gauge with semi-conducter voltage stabilser and unkown tank and float sender shows full and half for quite a while but everywhere else on the gauge seem to move quite quickly

Tony I think that calibration of the guage is a good idea if your gauge isn't showing too far out
Nigel Atkins

My Healey Frogeye gauge was way out - plummeting from full to half full in about about 20 miles, then falling eratically to empty at about 100 miles. When the engine had to come out for a five-speed conversion the problem came to light - earth strap missing, or rather left unbolted at one end by previous owner. But more to the point, I had a tip from Alan Anstead which seems patently obvious, but I hadn't thought of - use a bamboo cane as a dipstick. Turned out that when my tank was showing empty, there was still two inches of wet on the stick, in other words a good 50 miles or so of fuel left. Simple and effective.
C Whiting

<<if you're going to run until you completely run out then I suggest a fuel filter just before the carbs to catch possible rubbish at the bottom of the tank
>>

I keep reading this advice from various people.

As the tank pick-up pipe is fixed and not attached to a float, why should it be more likely to pick up any debris from the bottom of the tank when the fuel level is low?
Dave O'Neill 2

all the more reason to have a fuel filter all the time, plus it's then very easy to see if fuel is actually getting to the front of the car at least

TBH I'm not sure why it would be that more muck would get through on an tank almost empty, I think it's a case of muck or slime being at the bottom and a matter of it not being pulled out whilst a thinnerliquid is there??? - I'm no petrochemist as you can tell
Nigel Atkins

<<As the tank pick-up pipe is fixed and not attached to a float, why should it be more likely to pick up any debris from the bottom of the tank when the fuel level is low?>>

I believe the theory is that the less amount of fuel remaining in the tank the more it sloshes about and holds more dirt in suspension.

Dave
D MATTHEWS

This thread was discussed between 05/05/2011 and 16/05/2011

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