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Hows your G-car fuel gauge accuracy? - Fuel System/Carbs - The Lotus Forums #ForTheOwners Jump to content


Hows your G-car fuel gauge accuracy?


snowrx

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Just did a weekend away to the LOG40, and got to spend lots of time watching my fuel gauge enroute.  Mine will register above the full line when filled, then give me 130-160 miles before dropping to the full mark, and continues to read higher than actual fuel to around half full, then begins a race towards the bottom of the gauge below half tanks.

My temp gauge works fine, so I assume the voltage regulator is good. Battery voltage is steady. So barring the usual issues with fuel shifting in corners and the difficulty in fully filling some cars tanks, what is your experience with the Smiths fuel gauge as fitted to the early eighties cars?  I'd assume my sender is tweaked or has been replaced with the wrong one, but the car is pretty original otherwise; and I don't want to pull the sender only to find "they all do that sir". I suppose I could add resistors in series or parallel with the sender to at least get full tanks to read at the top line, and see where that left me as to the rest of the gauge travel.

 

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Hey Thomas,

Haven't a clue what to expect on gauge progression as I've yet to drive my S2, despite owning since '97! I wonder if your gauge is reading at all different lately as compared to earlier times, perhaps indicative of slow fail of the rheostat? On tinkering with external resistors I did so with the '64 Elan formerly owned and was at least pleased to have progressive accuracy in the range of lower fuel levels.

Cheers

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Mine is broadly similar.   i.e. starts as full, reads full for a period of time, then drops fairly progressively until 50%.  Stays on 50% for ages.  Then drops like a stone after a certain point.  (but that's fine, as its most sensitive as its nearing empty). 

NB Doubt I could get 360 out of mine, but I never brim it and have never run it empty, so not sure what actual max range is.       

Edited by 910Esprit
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Mine's not quite the same but way off linear so I mostly ignore it.  I also set the trip each fill but don't usually leave it 360 before the next.   The issue for me is that the low fuel light starts flashing on some corners and catching my eye from about an indicated 1/3 full and becomes increasingly frequent as it drops further.  Its a distraction I don't need so I generally fill up again relatively soon after despite "plenty" of fuel left.   I also find MPG varies significantly depending on what I'm doing.  I did 350 miles on Monday - mostly motorway/dual carriageway on a full tank and its showing about 1/4 full at the mo.  When I did Castle Combe in May, I needed a refill at about 200 miles.

Loving Lionel and Eleanor......missing Charlie and Sonny

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Not sounding good for the OEM system. It's not critical with a 4-500 mile range and an operating odometer, but an annoyance.

Like I said the gauge goes past 4/4 to the stop when fully filled, took 11 US gallons to fill when showing 5/8 full, and 14.2gal to fill when showing a 1/2 tank, leaving ~7.8 gal in the tanks.

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I think its better to go by miles in the Esprit. The gas gauge suffers from 'mood swings' a LOT!🤪 (Our '88 has the VDO gauge)

 

Of course, the mileage you get per tank is going to vary quite a bit too...those last 3 - 4 gallons take FOREVER to top up, especially in locales with vapor recover systems on their pumps. 🥵

I remember the low fuel light coming on at a Road Atlanta HPDE after one session. I must have been turning some wild G-forces on RH curves...when stationary, the gauge was 3/4 full.

Hey, if the engine runs, you can't be out of fuel yet.

Atwell Haines

'88 Esprit

Succasunna, NJ USA

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My 87 Turbo gauge is more of a approximate rather than absolute, reads way over full when first filled and the low fuel light flashes intermittently once down to about quarter.

I replaced the 10V ref mechanical switcher with a small adjustable voltage regulator PCB from Ebay so I have a known good reference and the gauge became more consistent, but its still somewhat on the enthusiastic side.

 

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Checked my sender with 7 miles on a full tank, and am seeing 14 ohms. Power from the stabilizer was 10.03 volts.

I haven't seen definitive specs for the sender, but I think it's supposed to be 30 ohms full and 190-200 empty, maybe going open circuit at the bottom?

Anyway, I'm going to add a series resistor to the gauge wire to bring the needle closer to the full mark, then see how that affects the balance of the scale.  Miles to go before I'll know. 

 

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OK , so with my 14 ohm full tank sender reading. I tried some resistances to see what the gauge would show;

-22 ohms took it down to 3/4

-10 lined it up with the 4/4 mark 

-8 ohms took it to a needle width above the 4/4 mark

So I made a pigtail with a 10 ohm resistor in it and put it inline with the GB wire, and I'll see how it turns out..

Sender Pigtail (2).JPG

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  • 4 weeks later...

Ok finally put the last frosty miles on this morning to get the tank down to an indicated 1/2  with the 10 ohm resistor in series with my ~14 ohm full sender.

I had to put just about 11 gallons in to fill.  The fill valve started clicking off at about 10.4 Gal, and I persisted longer than usual cramming more gas in and managed to get 11.7 in total.  So certainly on line with 1/2 of my listed 22 US gallon total capacity.  Close enough for me, although running the tank down to 1/4 will have to wait till next summer. My guess is it will still be non-linear at low levels, but at least my gauge is now more accurate at normal usage levels.

 

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