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fuel gauge or fuel sender?


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HI All,

winter is coming to an end (finally) here in Oz and starting to get the car out more.   I have a question that I am hoping someone can help with though.  My fuel was about 1/2 on the gauge, so went to the service station and filled up - right up.  When I got back in the car, the guage now only shows 3/4 full.  i have driven it around for about another 1/2 hour, and the guage is still showing 3/4 - so clearly, it is wrong.   So, my question is - would it be the gauge that is wrong or the fuel tank sender?  How can I check?   I know on the old holdens (here in australia), you could disconnect the fuel sender wire from the tank and 'short' it out and the gauge should read 'full', but not sure about lotus (or where to find wire anyway !!).

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I suspect you may have sorted this by now but I just fixed a similar problem on my car. It turned out to be a leaking float on the sensor. The float was slowing filling up and sinking so it would regi

probably the voltage regulator, a 10V supply is used for fuel and temp gauge. I am assuming it is the same as the Eite/Eclat of same vintage. On Elite it is located on back of speedo. You may notice temp and fuel changed together.

 

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thanks Clive - that is an interesting comment as my temp gauge has show high ever since I've had it (albeit, I have had the car nearly a year, but only driven it about a dozen times) and I was wondering if there was something wrong with my cooling too.   However, the fuel gauge and temp gauge are different are they not - insofar as the fuel gauge shows an 'instant' reading when the ignition is on - but the temp gauge is a progression based on temp of engine?  Is the voltage regulator replaceable?

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7 hours ago, hepkat63 said:

thanks Clive - that is an interesting comment as my temp gauge has show high ever since I've had it (albeit, I have had the car nearly a year, but only driven it about a dozen times) and I was wondering if there was something wrong with my cooling too.   However, the fuel gauge and temp gauge are different are they not - insofar as the fuel gauge shows an 'instant' reading when the ignition is on - but the temp gauge is a progression based on temp of engine?  Is the voltage regulator replaceable?

Both gauges work exactly the same: the resistance in the sender determines the voltage that reaches the gauge and this causes a deflection of the needle. The reason the fuel gives an instant reading, is that the resistance in the level sensor is a certain value for a certain level, right from the start. The resistance of the temperature sender will decrease with rising temperature, causing the needle to start low and then rise. A high resistance (open circuit) will give a low (zero) reading, low resistance/short circuit will give a high/max reading in both gauges, so relatively easy to check. Inside the fuel tank there is a float connected to the variable resistor in the sender, as this float lowers with decreasing fuel level, the resistance will increase and the needle o the gauge drop. If the float is wrongly adjusted, this will account for an incorrect or offset reading. It's good to check the voltage coming from the regulator just to be sure, but I wouldn't worry about the gauges as long as there is movement (especially in the temp gauge). You'll soon figure out how the needle position relates to the actual fuel left.

I have made many mistakes in my life. Buying a multiple Lotus is not one of them.

 

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Voltage regulator failure...usually it becomes intermittent and gives battery voltage instead of a regulated 10volts. This causes the gauges to OVER read....I used to get palpitations when I spotted the temperature gauge at astronomic readings, until I realised that the fuel gauge reading had also shot up, and a look at the wiring diagram gave the reason!! Now i have a new regulator, everything is much more believable. If your fuel gauge reads 3/4 when the tank is really full, the most likelty thing is that the float has got stuck. It's reasonably easy to get it out to check.

Scientists investigate that which already is; Engineers create that which has never been." - Albert Einstein

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When my voltage regulator when potty the needles on the speedo and temp gauge would dip at the same time, read low and then creep back up to where they should have been. They would also flicker occasional. Replaced with t a solid state one and all good since.

Pete

Pete '79 S2

LEW Miss September 2009

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doesn't sound like the voltage regulator is my problem then really.  Yep, maybe fuel gauge stuck - would make sense, as car doesn't give driven much and probably sat around with the same level in the fuel tank for a while.  Yes, seems easy enough to take the sender out of the tank (i guess !).  Q:, is the sender only in one of the tanks?

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  • 11 months later...

I suspect you may have sorted this by now but I just fixed a similar problem on my car. It turned out to be a leaking float on the sensor. The float was slowing filling up and sinking so it would register progressively lower fuel levels even after fill ups. It was a very slow leak over a period of weeks so wasn't an obvious fault. You'll obviously need to remove the sending unit and check the float to see if there's some gas in it. It doesn't take much of a leak to cause it to start to sink (mine was only about 1/4 full) so be sure to actually remove the sending unit from the tank and take a close look. The good news is a new float is cheap and easy to come by - worth having one on hand if/when you check to see if that's the problem.

Edited by 2many cars
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This is why aeroplane fuel gauges used to have cork floats...they can't get punctured!!

Scientists investigate that which already is; Engineers create that which has never been." - Albert Einstein

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I had a fuel gauge showing what I knew to be less than what was in the tank and it turned out to be a leaking float. I got a replacement from sj sports cars and that sorted it.

Good luck , hope you sort it out. 

Robin 

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Do we have figures for sender resistance, full and low? My instruments are being serviced and i wish to provide the chap with those figures.

Cheers

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