Which one of your three cars so we know which wiring diagram to choose.

 

Brinny
The sender is, I believe, a device which alters its resistance as temperature changes, allowing a variable current to earth. If you pull off the connector, and just quickly touch it to earth, engine warmed up and running, I think a helper in the cabin should see the gauge move to H. If it does not, I would test the wire between the sender and the gauge multiplug for continuity. After that, test the flexible and its path to the gauge. The same fuse (no. 4) does all the minor instruments.

 

Is this all happening on the original wiring (engine compartment) ?

 

The coolant temp sensor varies its resistance from 9.2 k ohms at -10 C to 0.190 k ohms at 100 C (this per the engine setup guide). I suppose you could simply measure the resistance of the sensor and see if it's close to the ambient temperature (this assuming that the engine hasn't been run in many many hours). The engine setup guide is, I'm sure, somewhere in the docs section. It's actually titled "XH-S Engine Performance" and applies to 1987 MY V-12's and earlier. Might be the same for later models too.

Another thing to try would be to disconnect the sensor and put a 450 ohm resistor across the leads. That should fake the gage into thinking the temperature is about 60 degrees C.

This could also be a problem with the instrument panel. Each gauge gets power, ground and signal from the pressure of a screw pushing against a solder pad. If it's hard for you to mentally picture this, that's a good thing, as nobody in their right mind would think this would be the proper way to wire anything.

Anyway, the table for the coolant (and air) temperatures is on page 13 of the guide.

Thanks,

John
1987 XJ-S V12

 

 

 

 

Is that the one on the air filter trumpet? If so this is for air intake temperature.

The gauge sender is on the RH water rail and is a single wire sender, ground is via the sender case to the engine.

 

 

AHA, that be the one for the LH electric radiator fan, oops.

 

Brinny
The gauge sender is on the A bank front water manifold on the casting, on the of of it, just rear of the thermostat. It has one wire coming from it that goes round the front of A bank into the V under the compressor.

 

 

No.

 

 

IMO & my 91 12cyl these barrel gauges are not very accurate. I installed two Auto Meter (AM) temp gauges & one oil pressure. I also kept the stock gauges connected. The AM sensor's are in the water rails. Temp comparison is 210 F on both AM's while the needle is only at the bottom of the "N", I don't know exactly what this is in actual degrees. Believe me , I have a lot of time & money in those stock gauges, testing, wiring, & sensors.
The stock barrel oil pressure gauge & sender had leaking problems & inaccurate also.

 

I believe it is more a question of repeatability than inaccuracy. I would bet that for a given coolant temp, two different cars' gauges might well be at different positions; but I would also bet that each car's gauge would be at its same position for that given temp repeatedly, and that it would respond to changes properly. Thus, knowing where your car's gauge normally sits is important, so you know when it moves what that implies for your car. And having said all that, cleaning up the rubbishy gauge contact-system which consists of a screw head touching a copper contact, is well worth it.
Now I am not saying the OEM barrel gauges are as good, well made, as easy to read, or dead accurate as aftermarket top notch kit like AutoMeter; but they are quite OK for their purpose.
Where did you install the AM gauges? have you got a photo, as in principle I like the idea, as long as I can hide them and not spoil my interior's look.

 

The three AutoMeter gauge's are mounted in a pod I also bought through the AM catalog. I reworked the 3 gauge pod to fit into the clock/ trip computer cavity. That is about the only place I considered to mount gauges. This means giving up the clock or trip computer. A man on this Forum or JagLovers Forum fit 3 smaller gauges without any pod & fit flush & really looks great. I wanted Smiths, AM, or Stewart Warner & they only come in larger size.
My whole concern was I wanted to view accurate temp reading on both sides of the engine and getting sick of oil gauge/sender issues.
Trying to post pictures is a whole other story

 

You know if anyone has tried pillar side mounted gauges? Like on alot of cars, diesel trucks come to mind. I want a complete set of digital gauges for everything but my god there is nowhere to put it even if you somehow safely trim or remove the faceplates they usually come in. Might just have to sacrafice the glove compartment.

 

Hell no!! A-post mounted gauges are so ricer!