My petrol gauge doesn’t function. I’ve got a spare E-type gauge installed now and while it serves to fill the hole in the dash it registers full regardless of tank level, so pretty useless. While my original is awaiting repair is there a non-original alternate gauge that can be installed in the interim?
I’m guessing after 54 views and 24 hours the answer is no.
The sender works fine so I at least have the low fuel level warning light to go by till I can get the gauge sorted out.
Anybody have a procedure to test and troubleshoot the XK120 petrol gauge?
Sorry, I have no procedure re. the gauge testing, however, if your fuel level warning light is functional you should be able to manage. My gauge has a nasty habit, once it is down to about one quarter full, of locking on empty. This is usually produced when turning a sharp corner. As my notes show I average 20-22 m.p.g. I calculate that when the light comes on and stays on I am good for about 40 miles. At the point that it lights on up any subsequent drive I always carry a gallon gasoline container so as not to get caught out. It has only happened once in the last 20 years or more!
The sending unit topic has come up quite often.
A full reading on the gauge means the wipers are all the way at the green/black end and/or there is no resistance from the green/black wire to ground.
Pull off the green/black wire and touch it to ground with the key on and see if the needle swings between empty and full.
Now pull off the cover and see where your wipers are.
Now if you want to try fiddling with the gauge, there are two little nuts in slots on the back. Those adjust the position of two magnets inside the gauge.
You want the needle to swing freely between those two magnets.
Thanks, Chris. I’ll just keep the tank fairly full. I had the old girl out for its first Cruise Night yesterday. It attracted a fair bit of attention, but mostly from older Brits …
, here with the missus in her appropriate 50’s femme fatale garb
That bump above the bootlid is a removable magnetic third brake light. I’ve also added removable rear- and side-view mirrors … my neck flexibility ain’t what it used to be
Yes, it does seem like it’s a pretty simple construction, Rob, if only a little delicate. I’ll (very carefully) take the case off and check the continuity of the two copper coils. I think the new sender’s working ok but I’ll take your advice and verify it. My original sender was very stiff but I’ve got it actuating well and resistance readings on the multimeter at various arm positions look reasonable. I may swap it back in.
Adjusting these undamped fuel gauges is a real black art, in my experience. I always try to match sender to gauge on the bench before installation. Changing either the gauge or the sender in your system will lose all the correct positions, so I always try to match sender to gauge on the bench before installation. You can read the resistance produced by the sender with a meter quite easily, but first make absolutely sure that the float can sit where you want it at the top and bottom of the tank. Don’t forget to check there are no baffles or vertical plates in the way of its action.
Adjusting the two coils on the gauge is real fun - a tiny change to one throws the first one out, and so on… I tend to settle for the gauge sitting on full for the first half of the tank, so that when the pointer starts to move, I have to watch it more closely. As long as the pointer swings on corners, you know you still have petrol…
I suspect a MKVII petrol gauge would work, they look the same, but apparently need some modification to fit properly into the XK dash
I also have a working sender that I was going to sell until I accidentally crushed the metal float (which wasnt in good condition anyway)
I did read the min/max resistances and I think it was in the order of 10-170 Ohms.
Looks great! I hear you about the neck, I find backing mine into the garage is now becoming a real pita, especially with the drophead top obscuring the wing line!
I will be in touch after our forecast hot spell passes about taking a drive down. It occurred to me that I probably should try and do it in June before things really heat up in July/August, either that or leave it 'til the fall. I find top down driving in blazing sun when the temperature is above 30C ceases to be enjoyable, it’s why I find spring and fall the best.
See the link here: XK 150 Fuel Sender - #9 by clivejer.
I was thinking that myself, Roger, since I have both gauge and now freed-up original sender out of the car. Should be some pleasant Sunday afternoon entertainment if I don’t manage to destroy the gauge in the process - I suspect I may have a disconnect internally or grounding issue somewhere between B and T terminals and taking the gauge apart doubtless requires some delicate handing to avoid breaking that delicate pointer
That’s consistent with what I’m getting on the original sending unit, Tony, so encouraging that at least that part of the equation is confirmed.
I’ll look forward to it, Chris.
Thank you, Clive! This may be just what I need to educate myself on the thing. I’ll study it right after I hit the reply button …
Alright, I’m seeing already from that, Clive, my understanding of how this gauge functions is as defective as it is … time to take a break and read it over carefully before I proceed. Thanks! Just what I needed.
Just rechecked the resistance readings of my original sender and it’s showing 88 Ohms in the full position and 4 Ohms empty. Those numbers are closer to those @Eric_Capron reported here:
I think the new unit I installed showed considerably higher readings.
I have heard that the new units are over priced and not accurate
This may well not be the case with others, as only complaints usually come forward
I have got several old ones working
I expect a MK7 and XK120 would have different resistances based on tank differences
The resistances are from memory, the low one should be about right
Differences in sending units would be related to bends in the float wand and float radius from the pivot point.
Differences in the gauge would be in the mounting tabs or lack thereof.
Well, Clive, that MG tutorial did the trick!
I read it over a couple of times and took the face off the gauge, magnifying glass and light in hand. Looked it over thoroughly and could see nothing amiss. Then noticed the little blob of solder on the right side coil plate with nothing attached. Odd. Checked the schematic in the tutorial to learn there’s supposed to be a hair thin coil wire there. It grounds the circuit. Fished around with a dental pick and found the loose end tucked underneath. Almost invisible. Resoldered it, put the gauge back together, hooked it up to a battery and the sending unit, adjusted the position of the two coils and the gauge is now working perfectly. Happy camper.
I was quoted $200 to have the gauge refurbished but hesitated to send it off. Stuff gets lost in the mail and these later XK120 petrol gauges are virtually unobtanium.
Many thanks to all who chimed in.
That is the most common fault with them, and is relatively easily fixed
You may wish to take this chance carefully to wipe down the copper coils, and clean the point on the wiper
I am inclined to think my MK7 LH sender would still be usable if a new float was soldered on, but in the instance of MK7 with 2 tanks, each side wire is different length and shape for some reason
@Rob_Reilly , now as I recall, the MK7 gauge has 2 tabs to screw to the sheetmetal of the dash, and apparently the XK120 does not.
Its my opinion they could easily be modified to fit.
I would like to find out, as I have several laying around, and one is enough,
if the rest can be made useful to XK guys, that would be to the benefit
replica MK7 senders are very expensive indeed, this is the last one I have
I did carefully retain all the tiny screws that are involved with attaching it to the tank, they may be an obsolete size and save someones backside, does anyone happen to know what size they are?
AS.303/4H is a #3BA x 1/2" long cheese head screw.
Here is a gauge from a 120.
There are little clips that hold it in to the instrument panel.
The case of the XK120 gauge has a ring welded to it about 3/8” from the face. It mounts to the inside of the dashboard with two L-shaped clips, one at four o’clock and the other at 10 o’clock. With the dash installed it’s almost impossible getting at the cheesehead screw that secures the upper clip. The gauge has to be grounded in order to work so the ring, the clip and the inner dash where the gauge mounts needs to be free of corrosion.
here is a MK7 dash, you can see the two screws that retain all the gauges
The small gauges are ~ 1" deep
Although you cannot see it, the AMP gauge appears to have a very similar collar to the XK petrol gauge
I have heard from a member that the MK7 gauges can be made to fit XK with a “sleeve”, and a very quick look suggested to me that I could grab a beer can, pair of scissors and a few simple tricks and it would fit like a gem
Dont have an XK dash to experiment with
Clearly you would rebuild an original if possible.
If not possible, or none present, I would be surprised if they dont work.
I have one sitting around, and a bag of resistors, so I can check its response to various resistances
Thanks Rob for the screw sizes…I Google 3BA x 1/2" and they are available in round head, but when I tried the correct “cheeshead” profile, found none
Just to add a new detail for your upcoming book on “Trivial Jaguar things 2 or 3 people want to know” I have noticed the screws always are red, so perhaps that is a sealing compound as the hole penetrates the tank from memory
Thay can be difficult to get out without breaking off in situ
I used butane pencil heat on (removed and defumed tanks) to get them out easy
While my oil pressure/temperature gauge was awaiting repair I picked up a comparable, working gauge at a flea market for $10, ground off the two tabs and fabbed a sleeve out of PVC tubing to allow it to be mounted to the dash.
The gauge face is different from the original and the ether tube is a foot shorter but it otherwise worked out well. This is an entirely mechanical gauge so it doesn’t need to be grounded to the dash. If you were to use the same technique to mount the Mk VII petrol gauge to the XK dash you’d need to add a ground wire.
There are a couple of differences between the Mk VII and XK120 gauge, the face being the most apparent, but the latter also has a low fuel level warning light so you’d also need to either insulate the bullet connector of its Gy lead in the dash or disconnect it at the sender to keep it from shorting out.