Hi All,
The fuel gauge in my HQ has always read about half of whats actually in there. Yesterday after fitting a GTS dash I have realised that its probably the sender not the gauge. There is about 70 ohms of resistance between the sender and earth. From what the manual says, it should be 30 ohms when full, and 0 ohms when empty, so its acting as an open circuit therefore making the NEW gauge read past full. Id say the old gauge must have burnt out/got damaged hence the low readings.

I've tried 3 gauges and they all read past full, so I've disconnected it until its fixed so they don't get damaged as well. Is it likely the sender is buggered, or could it be something as simple as a bad earth between the fuel tank and the body? I've checked the resistance directly from the sender to earth and its the same as the gauge end so the wire itself is OK.

Bit of a poor design in my opinion, the gauge working in the reverse way to HJ onwards, as there is much more chance of an open circuit on the sender wire than short circuit...

If it is definitely the sender, are there any tricks to replacing it? Its a Statesman.

any help much appreciated.

quote:

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Originally posted by GeeR
I understood 70 ohms was about the correct empty reading for an early thermal sender?

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Yes & no.

The early sender is the magnetic type (0 ohms empty & 30 ohms full).

The late sender is the thermal type & is 73 ohms empty & 10 ohms full.

Dr Terry.

Hi Tour Director.

As GeeR said, an HQ 308 with factory a/cond uses a fuel tank sender with a different base. They have an extra hose fitting for the fuel/vapour return. The Rares ones suit the cars without factory a/cond. If Rhyss car has no a/cond, then his problem is solved. If he needs the factory a/cond type, then he will have to have his sender reconditioned.

Dr Terry.

Hi Rhys.

What a conundrum !!

Firstly 9/73 is right on the changeover from magnetic to thermal type fuel gauges, so you could have either type fitted. The oil gauge did not change type, so its sender is probably OK.

The dash earth strap must be connected, especially if the fuel gauge is thermal, otherwise it will burn out. So connect the earth strap permanently & carry out a few tests. Get a resistor substitution switch from Jaycar or similar & do some tests by substituting those values for the sender to see if you have a good working gauge & what type it actually is. If you cant find one of those switches, get several loose resistors close to the values of: 10, 25, 30 & 73 ohms & connect them in place of the fuel gauge sender & look at what it reads.

Remember magnetic type is 0 ohms (short to ground) empty & 30 ohms full. The thermal type is 73 ohms empty, 25 ohms for half & 10 ohms for full. Also the thermal gauges take longer to stabilise, so read it after 5 minutes or so.

This is one advantage of the magnetic type, they are not voltage sensitive & work much more quickly. The thermal type are usually more accurate.

Dr Terry

Edited by user Saturday, 21 February 2009 3:29:37 AM(UTC)  | Reason: Not specified

Dr Terry,
I have an update. The original large fuel gauge I took out is definitely thermal. I have opened it up and the right hand coil looks like it has got very hot and lost its insulation, but it isnt open circuit. Before I took the gauge out, it was reading about half of what was actually in the tank.

I put 20L of petrol in yesterday, and the sender went from reading 70 ohms, to 61 ohms. Does this sound correct?

I have tried two fuel/oil gauges, but I think they are magnetic. One is dated 1977 so must have been a spare part. Dr Terry could you please confirm if the GTS dash fuel/oil gauges changed from magnetic to thermal in 73 as well or did they keep using the magnetics until the end of the HQ range? The thermal mechanism looks quite big and Id say it would hardly fit in the smaller gauge! I thought that the early GTS dashes had much bigger print on the fuel/oil and temp/batt gauges, and the later ones had smaller markings, is this right? The two I have tried have the smaller markings/text.

Hopefully Ill get to the bottom of this soon!
thanks
Rhys

You could try this company in Osborne Park and ask them for some advice.ph: (08) 9240 6999 They are called Applied instruments.

Is EH magnetic type? I tested and read from 0-26 ohms. It waves like a clown as the fuel moves side to side on the side streets.

Hi Guys
Is there an easy way to identify early and late gauges. I notice that some have a pressed stell back on them whilst others are plastic. Also I have been told that there are different manufacturers for the two of them. One is a slow moving gauge or dampened to suit the tank without baffles, and one is a fast moving gauge that suits the tank with baffles. Any info would be appreciated
All the best
John