Smiths fuel gauge issue

Technical Area for all the problems you have in the garage
Post Reply
User avatar
agnoraan
Posts: 1271
Joined: Sun Aug 17, 2014 5:37 pm

Smiths fuel gauge issue

Post by agnoraan »

We're in the process of wiring up the new aluminium dash and have fitted a new Smiths "classic" fuel gauge. I'm sure that when the car was parked up the old Smiths gauge showed it had just under half a tank of fuel. The new gauge is showing a quarter full. Also, it's very, very slow to react to show the fuel level. has anyone else had issues like this and if so what did you do to cure it? I spoke with Merlin Motorsports who I bought it from and they didn't have an answer for it.
cheers..Nige
KevinW
T289R Member
T289R Member
Posts: 563
Joined: Mon Dec 14, 2015 6:29 pm
Location: West Sussex

Re: Smiths fuel gauge issue

Post by KevinW »

i would guess a well-damped fuel gauge is a good idea to minimise false readings from 'slosh'.
Spyda do a useful gadget to help linearise the usual crappy response of these sender/gauge combinations;

https://www.spiyda.com/fuel-gauge-wizard-mk3.html
User avatar
clive
T289R Member
T289R Member
Posts: 3392
Joined: Thu Mar 01, 2007 1:18 am
Location: Perth

Re: Smiths fuel gauge issue

Post by clive »

I have a lovely bottle of single malt. I'm sure when I last had a dram, it was half full but when I looked at it just now, it's only a quarter full too! It must be the weather.

I would check whether the new gauge requires a voltage regulator or not and did the old one?
Cheers, Clive.

(If I'm not here I'm in my workshop or on the golf course!)
User avatar
peterc
T289R Member
T289R Member
Posts: 2041
Joined: Wed Mar 05, 2014 9:05 am
Location: Surrey

Re: Smiths fuel gauge issue

Post by peterc »

Clive’s comment on the voltage stabiliser is probably the main reason. I do have a voltage stabiliser on my Smith’s gauge(s).

The important aspect of accuracy of fuel level detection is to get the arm long enough to register the correct level at both empty and full. I performed a lengthy task of taking measurements of the actual depth of fuel in the tank, the ohms from the sender and what the gauge read for every two litres poured into the tank. I wasn’t getting sufficient difference in ohms near the empty condition for the Spiyda unit to improve the gauge reading below 1/4.
After discussing with Spiyda we came to the conclusion that in my case the unit would only sort out the inaccuracy between half and full which of course is not when you are worried about fuel level.
The Spiyda unit is undoubtably very useful for odd shaped tanks especially where the shape changes between top and bottom.
For those members just starting that part of the build then get the sender arm correct and then the Spiyda unit would indeed even up the accuracy across the full range taking into account that the Hawk tank is bigger at the top than the bottom.
Peter C
User avatar
agnoraan
Posts: 1271
Joined: Sun Aug 17, 2014 5:37 pm

Re: Smiths fuel gauge issue

Post by agnoraan »

The car has a voltage stabiliser and it's working fine. The new Smiths gauge is a replacement for the old Smiths gauge, the only difference is the new one is of the "Classic " range. It's just so slow to move
Nige
User avatar
clive
T289R Member
T289R Member
Posts: 3392
Joined: Thu Mar 01, 2007 1:18 am
Location: Perth

Re: Smiths fuel gauge issue

Post by clive »

The new Smiths gauges have built in voltage stabilisers. If there is a three letter code beginning with A on the body this indicates it doesn't require an external stabiliser. (APG for petrol gauge I recall). If this is the case then you might have too low a voltage.
Cheers, Clive.

(If I'm not here I'm in my workshop or on the golf course!)
User avatar
agnoraan
Posts: 1271
Joined: Sun Aug 17, 2014 5:37 pm

Re: Smiths fuel gauge issue

Post by agnoraan »

Ah right thanks Clive. I'll tell Owain tonight when I see him, as he's doing it for me. The voltage stabiliser on the car works fine, but didnt know the gauge could have its own internal one
Cheers Nige
KevinW
T289R Member
T289R Member
Posts: 563
Joined: Mon Dec 14, 2015 6:29 pm
Location: West Sussex

Re: Smiths fuel gauge issue

Post by KevinW »

peterc wrote: Wed Jul 18, 2018 7:48 am Clive’s comment on the voltage stabiliser is probably the main reason. I do have a voltage stabiliser on my Smith’s gauge(s).

The important aspect of accuracy of fuel level detection is to get the arm long enough to register the correct level at both empty and full. I performed a lengthy task of taking measurements of the actual depth of fuel in the tank, the ohms from the sender and what the gauge read for every two litres poured into the tank. I wasn’t getting sufficient difference in ohms near the empty condition for the Spiyda unit to improve the gauge reading below 1/4.
After discussing with Spiyda we came to the conclusion that in my case the unit would only sort out the inaccuracy between half and full which of course is not when you are worried about fuel level.
The Spiyda unit is undoubtably very useful for odd shaped tanks especially where the shape changes between top and bottom.
For those members just starting that part of the build then get the sender arm correct and then the Spiyda unit would indeed even up the accuracy across the full range taking into account that the Hawk tank is bigger at the top than the bottom.
Peter C
Peter - if the Spyida unit is surplus to your requirements, would you be interested in selling it? Have been thinking of buying one anyeway as the crendon tank is highly assymetric.
Kevin
User avatar
peterc
T289R Member
T289R Member
Posts: 2041
Joined: Wed Mar 05, 2014 9:05 am
Location: Surrey

Re: Smiths fuel gauge issue

Post by peterc »

Kevin,
Sorry to disappoint but I didn’t buy one because of my discussions with Spiyda. He told me what I would need to do to be able to install/ calibrate and having told him the results and my concerns he agreed that his unit would not solve the bottom end and indicate the last 1-1.5 gallons.
So until I can pluck up the courage to rip out the tank and reset the fuel sender arm I make do with knowing that the gauge is at least fairly accurate at around the 1/4 mark (but no where else)
Peter C
Last edited by peterc on Wed Jul 18, 2018 8:22 pm, edited 1 time in total.
KevinW
T289R Member
T289R Member
Posts: 563
Joined: Mon Dec 14, 2015 6:29 pm
Location: West Sussex

Re: Smiths fuel gauge issue

Post by KevinW »

Fair enough Peter, I'll just have to stump up full price for a new one!!!
all the best, kevin
Post Reply