Fuel Gauges

Types Fixings Identification Calibration

Gauge Types:

Jaeger, early magnetic system, externally lit, FG2530/63 BHA4381:

Smiths, early magnetic system, externally lit, FG2530/70 BHA4381:

Smiths, Mk1 thermal, externally lit, BF2300/02 BHA4470:

Smiths, Mk2 thermal prior to 1977, shrouded pointer, internally lit, BF2223/00 and BF2226/00, BHA4685 and BHA4736: (Moss Europe)

Smiths, thermal North America unleaded 1975-76, BF2226/02 BHA5342:

Smiths, thermal, RHD, 1977-on, BF2239/00 AAU3032:

Unfortunately this gauge is very difficult to get at being immediately above the steering column.

Smiths, thermal, unleaded, LHD, 1977-on, BF2239/01 AAU3031:

Fixings:

Early fuel and dual gauge with external illumination fixing strap AJH5185 with thumb nut 17H932, and a spring washer: (Moss Europe)

Internally illuminated fuel, dual and round temp and oil pressure gauge fixing strap AJH5187 uses the same thumb nut and spring washer as above: (Moss Europe)

Identification:

There were at least eight part numbers for fuel gauges for different markets and years, and at least eleven different reference numbers, some of which share the same part number of course. Whilst for some it will be obvious which era and market they are for e.g. those emblazoned 'Unleaded Fuel Only' for North America and Japan at various times, and those with the plastic bezel from September 1976 onwards, others may have internal differences which affect calibration according to which tank and sender they are used with. From the beginning of MGB production to October 64 unstabilised Jaeger gauges (FG2530/63) were used, and from but even this seems to have had a Smiths variant (FG2530/70). The gauge below is a BHA4736 with reference number (partially concealed under the front part of the face, circled) BF2226/00. BF2223/00 used the same part number from November 67 for all markets, the change to BF2226/00 occurring around 1972. This gauge was used up to September 76 for UK cars, ending earlier as engines for other markets gained catalysts and the gauges (a labels at the filler) highlighted that only unleaded fuel should be used:

Later gauges from September 76 on with the upwards pointer have the identification number behind the lower part of the dial, as in this example of a temp gauge:

As far as I have been able to ascertain these are the various fuel gauges and senders used over the years for each market:

Part No.	Reference No.	Chassis numbers		Dates		Notes	Sender	Notes
BHA4214E	FG2530/63	101	47712- 48767	May 62	Oct 64	Jaeger, magnetic, externally lit	BHA4292	Screws to tank
BHA4381E	FG2530/70	47712- 48767	56742	Oct 64	Mar 65	Smiths, thermal, exposed pointer, externally lit	BHA4471E	Screws to tank
BHA4470	BF2300/02	56743	138400	Mar 65	Nov 67	Smiths, thermal, internally lit	ARA966/ AHU1027	Locking-ring to tank
BHA4736	BF2223/00	138401	153877	Nov 67	Aug 68	Shrouded pointer, Canada	ARA966/ AHU1027	Locking-ring to tank
BHA4736	BF2223/00 BF2226/00	138401	415000	Nov 67	Sep 76	UK	ARA966/ AHU1027	Locking-ring to tank
BHA4865	Note 1	138401	258000	Nov 67	Aug 71	USA, Sweden, Germany	ARA966/ AHU1027	Locking-ring to tank
BHA4865	Note 1	153878	187840	Aug 68	Sep 69	Canada	ARA966/ AHU1027	Locking-ring to tank
BHA4736	BF2223/00 BF2226/00	187841	415000	Sep 69	Sep 76	Canada	ARA966/ AHU1027	Locking-ring to tank
BHA4736	BF2223/00 BF2226/00	258001	382134	Aug 71	Jun 75	North America	ARA966/ AHU1027	Locking-ring to tank
BHA4736	BF2223/00 BF2226/00	258001	415000	Aug 71	Sep 76	Sweden, Germany	ARA966/ AHU1027	Locking-ring to tank
BHA4736	BF2223/00 BF2226/00	101	2903	Dec 72	Jul 76	All V8	ARA966/ AHU1027	Locking-ring to tank
BHA4736	BF2223/00 BF2226/00	258001	386267	Jun 75	Sep 75	North America except California	ARA966/ AHU1027	Locking-ring to tank
BHA5432	Note 2	382135	415000	Jun 75	Sep 76	California, 'Unleaded Fuel Only'	ARA966/ AHU1027	Locking-ring to tank
BHA5432	Note 2	386601	415000	Sep 75	Sep 76	Rest of USA, 'Unleaded Fuel Only'	ARA966/ AHU1027	Locking-ring to tank
AAU3032	BF2239/00	415001	523002	Sep 76	On	UK	11H5062/ ADU3218	Integral outlet pipe Note 3
AAU3032	BF2239/00	415001	443980	Sep 76	Sep 77	Japan	11H5062/ ADU3218	Integral outlet pipe Note 3
AAU3031	BF2239/01	415001	523002	Sep 76	On	Rest Of World (not Japan), 'Unleaded Fuel Only'	11H5062/ ADU3218	Integral outlet pipe
AAU3031	BF2239/01	443981	523002	Sep 77	On	Japan, 'Unleaded Fuel Only'	11H5062/ ADU3218	Integral outlet pipe

Note 1: The Parts Catalogue indicates changes in part numbers for all cars at November 67 with the Mk2, and also at August 69 (Canada) or August 71 (USA, Sweden and Germany) when they reverted to the metal dash part number again. However one source of a 1970 USA fuel gauge shows it has the same reference number as the metal dash cars, so what this first part number change represents is not known. Because the sender didn't change the electrical characteristics of the gauge won't have changed, so any of the gauges for that sender could be used if visually acceptable.
Updated July 2009: However the voltage stabiliser changed at the same time as the gauges, and it seems that with the wrong mix of gauge and stabiliser the fuel gauge at least gives incorrect readings. Mk1 cars used part number 27H 7819, Mk2 cars used BHA 4602.
Note 2: Clausager indicates LHD cars got different gauges with the new plastic dash of September 76, and the part numbers in the Catalogue do change. However he has two photographs of the North American plastic dash - one with chrome bezelled instruments and a 120mph speedo, and the other with plastic bezelled instruments and an 85mph speedo, the 85 mph speedo only arriving with the 1980 models in June 79. If his photos are 'correct' then all the LHD instruments must have changed again after the start of the 77 model year, possibly at the start of the 80 model year when the speedo changed, but the Parts Catalogue doesn't reflect this (by then it doesn't show the late change to the 85mph speedo either). One source of an early Californian 'Unleaded Fuel Only' gauge indicates it has the same reference number as the later gauges, so again the reason for the part number change is not known. Because the sender changed in September 76 it's possible it's characteristics changed, which may well need a different gauge from the earlier sender, but that would have been the case for the 77 model year chrome bezel gauges as well as the 80 model year plastic bezel! All very confusing.
Note 3: GTs got the sender with integral outlet from chassis number 412301, the roadster from 415001, however both were August/September 1976.

Calibration

This is for the Smiths thermal gauges used after October 1964, for detail on the earlier Jaeger gauges see Barney Gaylord's site.

Rear of the gauge (right way up) showing the slotted plates through the holes in the case. This is a old, spare gauge hence the scabby appearance. I used this when first testing my ideas for calibration, before I realised how easily damaged the slots were. Note that it is not required to open up the gauge for calibration, it is done from the back:

Rear of the mechanism out of the gauge, again showing the slots:

Front of the mechanism showing the 'F' slotted plate with the 'screwdriver' slot in the middle, the pivot at the top, and the limit stops at the bottom. As you can see adjustment is almost more of a case of pulling the slot towards the terminal post, or pushing it away, rather than turning it on its own axis as one does a screw:

Front of the mechanism showing the 'E' slotted plate with the 'screwdriver' slot in the middle, the pivot at the bottom, and the limit stops at the top. Note the heater winding is wound on just one half of the 'U' that is the bimetal strip. This is the ambient temperature compensation mechanism. Because one end of the 'U' is attached to the base and the other to the pointer, any ambient temperature changes cause the 'U' to bend equally in both halves of the 'U', so effectively the two ends stay in the same position relative to each other, and the pointer does not move. But when a current is applied to the heating coil, only one half of the 'U' is heated, the ends of the 'U' move relative to each other, and this causes the pointer to move. I only discovered this when heating the whole of the gauge to see how much ambient temperature changes affected it as I was of the opinion that the temperature compensation was done in the stabiliser. I was initially surprised to see no movement of the pointer, but then realised the significance of the 'U' shape of the bi-metal strip. Confirmed by laying a pencil soldering iron across first the unwound section, then the wound section, on the unwound section it caused the pointer to move backwards, whereas on the wound section it caused the pointer to move forwards as one would expect:

Showing the E plate fully adjusted to the left:

Showing the E plate fully adjusted to the right. Note the gauge is not powered, and just goes to show how much pointer movement is affected by a small movement of these adjustment plates:

Gauge unpowered, showing the 'cold' gap (A) between the ends of the bi-metal strip:

Gauge fully powered, showing the larger 'hot' gap (B) between the ends of the bi-metal strip. Note how the relatively small increase in gap causes full-scale pointer movement:

Unfortunately the 77 and later fuel gauge being above the steering column is nowhere near as easy to access, try removing the tach first: (Clausager)

Removing the bezel and glass - there should be three tabs on the bezel (A) folded over a flange on the case. The bezel needs to be twisted round until the tabs line up with cut-outs in the flange (B). However there is a rubber gasket which can glue things together, in which case the tabs may have to be levered back a bit with a screwdriver and the rest of the bezel eased away from the case flange bit by bit until it comes free. There should also be a square-section rubber O-ring on the outside of the case (not shown) to buffer the instrument against the dash panel: