I took out the instrument pack and discovered nothing out of the ordinary. Took off the circuit plastic, pulled out the instruments, cleaned all the connections, and put everything back together. Didn't undo the main ground in the left A post but it looked perfectly clean so I sprayed some contact cleaner on it and put the dash back together. All the instruments work great but the temp gauge is still pegged on the right within about 30 seconds of ignition. About 30 minutes after turning off the engine, I turned on the ignition without starting the car and the temp gauge went immediately to halfway between Normal and Hot. After a couple of hours, it finally went to cold.

Unless there is something else you guys think this could be, I'm thinking I should replace the temp sender. I'm having trouble with the part number, though. DBC3728 appears to clearly be the coolant temp sensor. I think DAC2583 is the temp transmitter I need to replace but I'm having trouble confirming that is correct for this car. Allan, can you confirm it?

 

The parts list says the part number is DAC11079, should be pretty easy to find. (DAC2583 is for pre-facelift cars)

Hope that fixes the problem

Cheers,

Allan

 

Thanks, Allan. I've ordered both parts. I'll let you know the results.

 

Replacing the temp senders had no effect. There's $50 wasted.

In addition, since I took took apart the instrument pack in the dash and cleaned it, my tachometer works only in the morning. When I first start the car, the tach works fine. When I start up to come home from work, it doesn't work.

So I'm going to finally do what Jim suggested and clean all the ground points.

Allan, it looks like I have to completely remove the dash to get to the ground point for the instrument pack. If you or anyone can give me any hints on shortcuts or things to avoid, I would really appreciate it.

I'm finding it hard to believe that this is a ground issue. All my ground connections look perfect--no rust, no corrosion. The only time I've ever seen electrical problems like this related to grounds, it's been because of rust or corrosive buildup. Regardless, I'm going to take apart the car and try to clean these connections as best I can.

One thing I did notice: Now, just turning on the ignition--without starting the car--is enough to peg the temp needle to the right. I wish I had seen this before the got the new senders.

 

Not surprised but at least now you have a spare

I still believe you have a connection problem and the fact that your tach is playing up reinforces that.

A couple of things to look at. The tach gets its signal from the coil. The tach signal along with the temp signal come in to the cockpit on the right hand side and connect to the dash harness at block LI134 which is down near the ECM. You could check to see if those connections are good.

After that the signals go directly to the instrument pack. Did you inspect both sides of the two plugs and make sure the plugs seat securely?

The ground is a likely candidate too. I know it may look ok but it is a good practice to clean and secure just to rule it out.

I'm not sure you can get to it from underneath but might be worth a look. Otherwise it's off with the dash

Well to paraphrase Sherlock, when you rule out the probable, you're left with the improbable If all the connections check out fine, then you might have a kooky temp gauge but the fact that the tach is playing up too makes me doubt that.

Stick with it, you WILL solve this problem!!

Cheers,

Allan

 

Ok, a little different today. Tach is back to working all the time--at least it did today. The temp gauge is doing something new, though. Immediately after start, needle is pegged to the right. After about 5 minutes of driving, needle hovers around H and stays there. This is similar to what it was doing at the beginning but it used to hover around N.

I tested the temperature at the thermostat housing with an electronic meat thermometer immediately after I got home and got a reading of 175 F. I can't seem to find the specs for normal operating temperature anywhere but this would seem to be low.

Allan, is there any possibility that my car is overheating now and I just can't tell?

 

Ok, so when you measured the temp at the thermostat housing, was this after the car was completely warmed up, say after a half hour of driving or just after 5 mins?

If it was fully warmed up then I would say that the engine was actually running very cool. Even if you have an 82C thermostat (standard is 90C I think), I would expect temps in the mid 180's at least for a fully warmed engine, so 175 seems quite low. My car generally runs at between 195-200F and can get as high as 215 or so in very hot weather and stop and go traffic. For most cars 195-200 is thought to be ideal temp for good combustion.

If it was just after 5 mins, then 175F would be very believable. I'm assuming of course that your meat thermometer is fairly accurate? If you want to be more certain, perhaps you could borrow or buy an infrared temp measuring device? You can get a decent one for $25 or so.

The unstable readings still indicate a bad wiring or ground connection IMO. Perhaps you could try the old wiggle test. Have someone monitor the gauge while you wiggle the connector at the transmitter. Do this with the engine running. Then disconnect the transmitter connector and ensure that the gauge pegs to the left. (don't burn yourself )

After that it becomes a bit of a hunt, perhaps you have a bad connection in the harness, a dodgy ground or a poor solder joint on one of the connectors. My guess is that it's one of these but there is also the possibility that you have a duff gauge. I think this is less likely though.

Keep at it

Cheers,

Allan

 

Thank you for your input, Allan. Been a while I know but I just got back to this. I have been keeping my meat thermometer in the car and checking the temp regularly. To answer your question, I tested with the engine running after I got home from work. I can't seem to find specific specs on running temps for the 94 AJ6 but it seems mine is not overheating.

Finally, the gauge just gave up the ghost pretty much altogether. I took it out and today put it on the bench with the original temp sender. I put the sender in hot water and the needle goes right to 3 o'clock. It appears to stick there and when I turn off the power, it's as likely to go clockwise as counter-clockwise back to C. I can't seem to get it to read anything like a normal temperature. It appears to now be hypersensitive and only registers cold or volcanic.

My testing seems to indicate the gauge is bad but I have seen much reference to adding another ground or an inline resistor. Allan, you mentioned the idea of a ground but all my other problems went away after I made sure I had well seated connections to the back of the instrument pack so I am dubious. The inline resistor suggestion throws me. Why would an XJS, after running great and the temp gauge working fine for years, suddenly need a resistor unless something is suddenly wrong with the gauge? Messing with the mechanism of temp registration is scary to me as I know just what kind of damage overheating can do. My guess would be that this model gauge has a history of becoming faulty. It does have 190K miles on it, after all.

It seems my next step is testing the sender against another gauge--preferably one that shows actual temps--but I'm assuming all senders are not created equal. After that, I guess I will have to try and repair the gauge but I have no idea how. Finding another one seems unlikely.

Anyone have any further suggestions?

 

my temp gauge is acting almost identical to yours

I have tested actual temps at the t-stat housing with a inferred laser thermometer. and get 175-180 at the t-stat housing. temp gauge reads just under the red line on the gauge at normal temperature. will occasionally peg itself all the way out. normally as the temp of the engine is still cold but warming up then drops back down as it gets closer to normal temp.

so far all i have done for diagnostic is unplug the sensor and verify that the reading drops to dead cold and test pegged against ground. and taken a lot of readings with a laser thermometer. I ordered a new sensor. has not arrived yet. but i am hoping that fixes my problem. but I see that you replaced the sensor and the issue continuous. so this may be interesting

 

im still waiting on me sensor but i was doing a bit more messing around with it yesterday as it was really nice weather. one thing that i noticed is im getting battery voltage at the temp gauge sensor, is the temp gauge suppose to run on bat voltage or is it suppose to be regulated 5v

 

Thank you for the confirmation. I have been unable to find a spec providing normal operating temperatures.

This is the behavior I got after replacing the temp sender. The problem started with the gauge not registering at all and then going to N after a while. Later, it would peg at 3:00 and come back to N. I replaced the sender and it pegged at 3:00 and came back to H. Sounds like you're about halfway through the cycle.

Yes, my guess is your sender is fine.

I did manage to find a replacement gauge. Waiting on its arrival, now. I'll let you know the results probably by next week.

 

I'm sure between the both of us having seemingly identical issues we will get it figured out.

i ordered a genuine jaguar sending unit from pauls jag, as iv read some threads about replacement sensors not reading properly and people adding resistors to correct the reading.

i don't think resistor will correct my current issues as its not a consistent up and down reading. i did however add resistance for testing by connecting a test light in series with the sensor and it did lower the reading on the gauge.

 

I'm by no means an expert so hopefully someone can give a better answer (are you there Allan?). But just to clarify, there are two temp senders in the thermostat housing. One has two leads coming out and I believe this is part of the ECS. The other has a single lead and connects to the gauge. It is a thermistor that provides resistance for its ground connection from the engine block to the gauge. As temperature goes up, resistance goes down, and the gauge is actuated toward H as resistance decreases. +12v is provided to the gauge from the ignition hot on pin 12 (I think) of the 14 pin connector to the instrument pack. Pin 13 is the ground connection to the lead on the sender.

 

That's interesting. I had not heard about the need for a resistor from replacement senders not working correctly. Before I got a parts catalog, I almost put the wrong replacement sender in but Allang set me straight. Now I have a catalog which confirms the right part number DAC11079.

When I get the replacement gauge, I'm going to test it on the bench with my original sender before I put it in the car. I'll keep you informed.

 

the 1 wire sensor is for the gauge the two wire for the ecm. it should work as a variable resistor.

i should bench test my sensor but as i already ordered a new one as standard diagnostic points towards a bad sensor. im just going to wait untill the new one gets here.

i would be curious if anyone knows if the temp gauge is suppose to be regulated 5v like the ecm sensor or battery voltage.

the sending unit i have coming is the same part number and suppose to be a genuine jaguar sensor

If someone with a properly working temp gauge could unplug there 1 wire sending unit turn the key on and test voltage between ground and the wire and tell me if its 5v or battery voltage it would be appreciated.

 

i have a bit of a update for you.

my new temp sensor came today

here is what they sent me as a dac11079

i went back and more carefully read the e-bay listing and it says

"This is Jaguar's recommended replacement for DAC11079 - long thought extinct elsewhere, but not at Pauls...."

"I thought i was getting a dac11079 but it actually does not say that you are getting a dac11079 you are getting jaguars recommended replacement for the dac11079"

it does fit and look right and everything else.



installed now i have proper sweep from dead cold to full warm but it was still reading warm

175*



so i installed a potentiometer (basically a variable resistor) i had laying around. (i think it was a dirty pot i replaced in a guitar amp and threw it in my electrical junk box.) its a 20k pot witch is way too big for this application but put some wire and some connectors on it plugged it in and adjusted the gauge down



i just e-taped it out of the way for right now im going to run it like this for a few days maybe make some slight adjustments to it then if all is still well after a few days ill measure the resistance its set ant and wire in a fixed resistor

 

It is interesting that Jaguar used the DAC 2583 temp transmitter for most of their cars of that era but the DAC 11079 only for the facelift XJS. The series III saloon, XK40, pre-facelift XJ-S and even the X300 all used the DAC. 2583 In fact that transmitter has been in use in many British cars since the late 60's!!

I am curious why Jag changed the transmitter for the facelift XJS, especially as they were continuing to use it on the XJ40 and X300? It seems logical that they must have different resistance value ranges. As I have the DAC 11079 in my 94 XJS and the DAC 2583 in my 95 XJ6, I think I'll take some temp/resistance measurements to see. More anon.

 

it would be appreciated if you could do that.

thank you

 

Ok so after taking a few readings, these are my findings. All readings were taken with an IR temp sensor pointed at the same place on the thermostat housing just below the Coolant temp sensor. I cross checked my IR temp readings on the XJ6 with the temp readout of my scan tool and found the results were always within 3-4F which I think gives a reasonable level of validation. (Variance probably due to the emissivity differences between the housing and a black body source.)

94 XJS with DAC 11079 (B+ FEED VOLTAGE 14.22v)



67F = 1370 Ohms
78F = 1003 Ohms
94F = 665 Ohms
104F = 529 Ohms
130F = 222 Ohms
160F = 150 Ohms
180F = 125 Ohms
190F = 100 Ohms

This is the temp gauge on my XJS at a measured 190F




95 XJ6 with DAC 2583 (which is an Elmwood 81EL074 sensor. Elmwood are out of business) FEED voltage = 9.22v with engine running which I found odd.



68F = 865 Ohms
81F = 635 Ohms
94F = 465 Ohms
104F = 388 Ohms
133F = 222 Ohms
158F = 143 Ohms
180F = 100 Ohms
190F = 90 Ohms

NOTE: Apart from the senders being different, I believe the gauges are also. I found in one of the XJ6 manuals the following "The coolant temperature gauge is calibrated to indicate at approximately 'Normal' for a wide range of normal engine operating temperatures." Which indicates that the gauge effectively becomes an 'off-on-off' switch.

In contrast, the XJS gauge readout is always directly related to the resistance change and Jaguar just noted a very wide 'Normal' range on the gauge markings.

 

thank you for taking the time to take take the measurements for us.

although im doing better with the new sender, im still having some slightly erratic readings. part of this might be that im using way to big of a pot to try to calibrate my gauge. but im going to pull my cluster out again and clean connections again as well as add a additional ground.

one thing i found very interesting is although the resistance is much different on the lower end of temps the operating temp is only 10ohm difference.