I've fitted a new sensor, put a new plug on the wire to the sensor and tried a different gauge in my S3 XJ6, are there any common places the wiring would usually fail on these? Are the plugs by the brake servo where the loom from the engine bay goes to the instrument panel? If it is I guess I could check the wiring to and from this point to see if the problem is either side of the connection, or the connection itself.

The wire from the sending unit/sensor goes to a connector down low on the RH engine bay wall. Generally you find problems in that span, as engine heat bakes that section quite a bit

yes

Perfect

Cheers
DD

So I borrowed a probe pointer thing from my brother and managed to quickly trace the wire, I cleaned up the connection on the firewall plug and then checked with the probe pointer at the gauge connection, it's definitely getting a connection from the engine to the gauge but still not working. Anything else I can try?

sounds like it's not the wiring but the gauge. Substituting the gauge is the next step.

Electrickery is far from my strong suite

However, a radical idea in part. Check the S57 jaguar schematic to make sure your probe was for the correct wires.

Get a long wire. Connect one end to the sensor. Take the other through the windw in the door and to the guage. Now try.

Bench test the sensor with heat and the OHM meter. Unfortunately, new is ot always good !!

Use an IFR to see if there is temperature to measure.

Carl

Right pic is with the engine off, left is with the car running. It doesn't move further than that (different gauge albeit second hand).

This is the connector to the firewall which the probe sensor gave the beep to:

I gave the inside of the connector a clean with wire wool then sprayed a bit of WD40 in it after and used a precision screwdriver with a bit of rag to clean out the muck and dry it off.
I'll try running a cable direct tomorrow, I don't suppose you have any more guidance or a link on bench checking?
Thanks.

Did you already swap gauges or remove / access the wiring to the existing one ? I'm not at home with my cars to check the ohm values ( cold to hot ), but the temp sensor acts as a variable resistor in the ground path for the gauge ( looking at the S57 manual ). Since the fuel gauge looks like it is working, I'll assume the temp gauge is getting 12V+ as well ( same fuse circuit ).

I would try the following steps:

1 Remove the wire at the sender unit, any gauge movement ? Next ground the wire to a known good ground point, any gauge movement ?
If no to both, then either there is a wiring or gauge problem ( think you are already past this step ).

2 Remove the gauge or access the wiring with the dash pad removed. I can't remember if the gauge connects with separate wires or just one plug ( will check tonight ) so if separate wires remove the GU ( Green / Blue stripe ) wire from the gauge, connect a jumper wire to this gauge connection and do the disconnected / then grounded test above. If just one connector, then remove the gauge, run 12+ to the Green wire and do the open / ground test on the GU.
If the gauge pegs it's good thus a wiring problem, if still no movement then the gauge itself is bad.

I think it's most likely the connectors you showed above or the ones on the gauge itself being gunked up ( or even disconnected ).
Hope this helps.

Cheers,
Brian

with the engine running for some 25 minutes to bring it up to temperature, tap the glass of the gauge to see if it moves. Sometimes they get stuck.

Cracked it, I ran the wire from the sensor to the gauge and it worked, I checked with the probe again on the factory wiring and traced the fault to the plug on the firewall. It was making a connection but not a great one so I crimped the connector a bit so it was a tighter fit and hey presto!

Oil gauge decided it wasn't happy and that's stopped working now so I'll have to check the firewall plugs again but happy to be able to see the temp now!

Thanks for all the help

All right, success !!! Makes one feel good.

Jump the OP sensor to guage and see if that works. Need the engine running to make that test valid.

The OP sensors go bad. Been there done that. Mine did. I knew I had OP as my car is a lump with hydraulic lifters. No rattle meant OP OK. But, I got another. NOS from David Boger at Everyday XJ . OP good again!!!


Connectors just seem that on these cars, after decades???
o
Carl
Carl

Went out yesterday on a short trip, didn't go above 90, was going for a longer trip today and it overheated and dumped its water in the road 🤦‍♂️ luckily I'd just pulled off the motorway when I heard a pop before all the steam so hopefully it was just a pipe. Will investigate tomorrow.

Carl's suggestion on running a test wire is great, I do that all the time. Buy or make some leads or test wires about 24" long with a little alligator clip at both ends. Make sure the clip insulation is the same color. I have a black wire with black clips and a red set. That makes it easy to hook things up. If you have a long run, say from the engine through the window into the interior you need a long piece of wire then clip the test leads to the connection and then to the wire on both ends. Be sure to make sure to doesn't short at the clip, I use clothes pins to make sure they don't fall down and touch. With an old Jaguar you are always going to be working on electrical problems so having a pair of test leads in your tool box is going to make things easier. They also come in handy when you don't have enough hands to hold the multimeter probe to the connection.

Jeff

Thanks, Jeff.

I have a bunch of them

Carl

Any news on what burst??? Hopefully just a hose!!
really ruins your day being trailered home!

90 C or 90 kmh ?

Carl

I'm not sure what the cause was but it was a lower hose that gave up the ghost



90C

So I'm not sure what cause the car to overheat yet but I've ordered a new radiator hose set and a water pump, while I'm waiting on those parts coming and as there's no water in it I thought I'd put in a new thermostat in which I already had. I cleaned up the thermostat housing while it was off but in doing so I found the casting on the housing wasn't the best! My older brother works for an engineering firm so I think I'm going to have to get him to bung some weld in it and skim it.






Wish I hadn't found this but at the same time I'm glad I've found it sooner than later.

My brother welded the bit of thermostat housing which wasn't up to scratch and skimmed it, even powder coated it I sprayed the other half of the housing:






The intake flute was also looking a bit shabby so I cleaned that up and gave it a lick of paint:








It's not immaculate but looks a hell of a lot better than it did.

I need a brother like that!

I am surprised that the distressed metal did take the weld! Good work, Looks far better...


Probably the hose failrure as the cause of the over heat, rather than the over heat causig the hose failure.

Now, all the other hoses in the cooling system are suspect, alog with the heater hoses..
Carl

Hi, glad to see the gauge problem was just the corroded firewall connection.

Here are some pictures of the temp gauge wiring connections, and a way to quickly test it.
To test:
ground the case at the knurled bracket that holds it in the dash ( ground point for gauge )
briefly touch +12 V to the connector with the double solid green wires ( positive supply for gauge ) -- you should see the needle move left just slightly ( colder )
now connect + 12 V to that connector
briefly touch a jumper wire from ground to the connector with the single green / blue stripe wire ( from sender ) -- the needle should move full right ( hot )
don't leave it connected as I'm not sure if it will affect / hurt the gauge to peg the needle.

The red with white stripe is for the lighting in case it needs to be tested ( has a bulb in the metal case )

Once I find / measure the sender ohm to temp ranges, I'll post numbers here so the gauge can be tested for ACCURACY not just operation !

Cheers,
Brian

PS NOT responsible for anyone letting the Lucas magic smoke out !