Fuel tank with bolt in sender unit

[Harry]

Hi I have several left hand fuel tanks all appear to be mk 1 tanks one has a bolt in sender unit does anybody know what this would have come from.

[1071 S]

Don't they all (like my 63 S) ??? later ones (maybe still Mk I) have the bayonet fitting....

Cheers, Ian

[rich@minispares.com]

bolt in senders stopped @1964 - I think it was roughly when voltage stabilisers where introduced that the twist senders came in

[Harry]

I have several cars rangeing from 59 to 68 both 59 cars have twist in type retaining lock assuming tanks are original as they have no drain plug as body has no hole in floor for a drain. Also have several cars 63 on 850 to cooper s all of which have the twist type some of these cars I have had over 30 years so I am pretty sure tanks are original.

[AndyB72]

It could be an Innocenti one, off the top of my head the sender is held in by 8 small bolts and came in two sizes. If it still has the sender fitted it should have 3 connectors (two for the gauge and one for the low level light) and a pipe coming out of the middle that bends towards the back seat.

[dklawson]

Sorry to contradict anything said above but the transition from bolt-on to bayonet mount senders was in late 1964 (as mentioned above) when the voltage stabilizer was introduced. I understand that for a short period during the change there was a transitional sending unit that had the resistance range of the later sender but still bolted on. I do not know the dates for that transitional sending unit.

To determine what your car has and what your car needs for a fuel gauge is fairly simple. Connect a multimeter to your car's fuel sending unit with the wires disconnected. Either remove the sender from the tank or use a coat hanger through the filler neck to lift and lower the float. For the early senders and gauges that operate WITHOUT the voltage stabilizer the sender will measure about 10 Ohms when the sender is at "EMPTY" and near 90 Ohms when the sender is at "FULL". If instead your sending unit measures about 270 Ohms when empty and about 30 Ohms when full, that is a later sending unit and it needs the later gauges with the stabilizer. These resistance values are "nominal". Your actual measurements will likely be a bit different but close to what I mentioned.

As many of you already know, you cannot mix gauge system components designed for the voltage stabilizer system with those that came before it. You must use all early components or all late components.

BMC appears to have made the change to use the voltage stabilizer several years after the switch was made by Standard/Triumph and others. Regardless, a bayonet ring mount sender on a pre-1964 Mini would indicate that changes were made to the car at some point.

Hopefully Nick at MiniBitz will see this thread and be able to post some dates and provide additional information.

[cheleker]

Agree with Doug; except, I would say that the change from bolt-in was earlier in 1964, which would make the "transitional" sender a bayonet ring type. Take that as a "maybe" becasue it has been a while since I did the related research!
Regardless, pre-64, as Doug posted, and maybe a couple of months into 1964, would be screw in if parts are original to the car.

[dklawson]

Chuck, my car is either a late June or July '64 (I'll check the certificate tonight) and it had the bolt-on sender when I got it. I do not know the exact date the gauge system changed but I have always assumed it was rolled in with the other changes that happened in/around September of '64. Again, I am hoping that Nick sees this thread and can offer his comments.

[NickD]

According to AKD3509, the change from the senders retained by screws to those retained by a lock ring was at body no 23174 (in February 1964?). The lock-ring senders initially had the same stud & nut electrical connections as the earlier screw-in type and were used with the same fuel gauge. In September 1964 a revised lock-ring sender with Lucar terminals was introduced along with a new fuel gauge and the change to voltage-stabilised instruments. My September 64-build car has the lock-ring / stud & nut / early instrument combination

[dklawson]

Thanks Nick. That's a slower and muddier transition than I anticipated. Paraphrasing what you said, it sounds like a transitional sending unit would have been in use from February to September 1964... compatible with later tanks and non voltage stabilized gauges. Bolt-on senders until February '64. Does that sound correct?

[Tim]

So if you wanted to fit the later tank to an early car you could simply track down the transitional sender unit, which would physically match the later tank, but electrically match the earlier electrical system.

That sounds easy!

Tim

[Toby]

I think you guys are forgetting that the 64 tank with the sender that locks in had the drain tap on the underside. After that the tap got discontinued as far as I know.

[ricardo]

October 1964, tank has the drain tap.

[NZmember]

I have just purchased a '63 project with Austin speedo but came with a replacement tank with the twist in sender and lucar connectors. So have the connection problem described.
Without replacing the fuel gauge is there any way to connect the later sender with a voltage stabiliser etc?

Thanks
Derek

[matic]

hi sirs,
i got question. if i use 5.5gallon duel tank with locking nut version and late sender init, what will i modify the original mk1 fuel gauge to suit this sender? do i need to put the voltage stabilizer? is the voltage affecting to the original mk1 guel gauge?

warm regards
ink

[Tim]

The early and late senders are entirely different electrically. The resistance range is different, but more importantly they operate in opposite directions (one has low resistance when full, the other high). So there is no simple way to connect one to the other.

The only way I know to connect mismatched senders and gauges is to put some clever electronics in between which can read the sender and translate its output into something the gauge understands. Something like this https://www.spiyda.com/magento/index.ph ... d-mk2.html

Tim

[dklawson]

There is nothing I can add to Tim's excellent summary. You cannot mix the pre-1964 and post-1964 gauge system parts.

That "Fuel Gauge Wizard" linked by Tim sounds like a GREAT buy at 40 GBP. That's less than the cost of just about any single gauge component purchased new.

[matic]

hi sirs,
thank you so much for a great information.

by the way, i have more question about fuel gauge wizard. according to the website, the seller ask about the gauge type and sender unit. if i like to use an original mk1 fuel guage with late locking ring, what do i select?

for example, what ohm of the original fuel gauge? however, the ohm of late sender is 30-260 as mentioned on the selection option.

thank you so much and regards
ink

[NZmember]

Well I'm impressed, that is a great item to have developed. Thanks for posting.

[dklawson]

hi sirs,
thank you so much for a great information.

by the way, i have more question about fuel gauge wizard. according to the website, the seller ask about the gauge type and sender unit. if i like to use an original mk1 fuel guage with late locking ring, what do i select?

for example, what ohm of the original fuel gauge? however, the ohm of late sender is 30-260 as mentioned on the selection option.

thank you so much and regards
ink

The early senders I have measured have a "nominal" range of about 10 Ohms = Empty to 90 Ohms = Full. The exact value of your sending unit will likely be very different. The later gauges expect a sender that has the nominal range you specified. If I bought the Gauge Wizard I would select "don't know... calibrate myself". It should not be hard to do and presumably be able to match your exact sender to the gauge.