QuestionQUESTION: Hi Howard,
I’m writing this as your responses to other people on line are very professional and comprehensive! The needle on the temperature gauge of my 1984 jaguar XJ6 does not go up to full operating temperature (i.e. to 85 / 90 degrees which is midway on the gauge or start of the green band). It only ever goes to approx. 75 degrees no matter what the driving conditions are. Would this be a faulty/inaccurate gauge or an indication that the engine is not running at optimum temp.? Any way of testing for this or what steps I should take?
One other problem that I have with the car is that the a/c has stopped working. It just blows luke warm air when I turn the knob around to the coldest position. Before it stopped working I had noticed that the a/c compressor was very noisy anytime the a/c or heating system was turned on (which was very annoying because to passers by it sounded like the engine was very rough!) The questions I have in relation to this are; is this level of noise normal for a/c compressors? Do you think that absence of noise from the compressor means the compressor needs to be replaced? Do you think the compressor is the reason for the a/c not working?
Thank you for taking the time to read this and for any help that you can pass on.
Frank.
ANSWER: HI Frank,
The sending units are in the end of each fuel tank behind each tail light assembly. Run the tanks low on fuel and you can jack the rear up and remove the tail light assembly and remove the sending units and with each out, reconnect the wires and tape or stuff a rag in the opening in the tank as you don't want a spark around the fumes. then turn on the ignition and hand operate the arm on the sending unit to see if the gauge goes full to empty. If it does not and the arm is free to move it's full travel it is most likely the gauge because the sending unit is a wire wound resistor and is most likely unable to change in resistance. The gauge uses a full 12 volts and does not use a voltage stabilizer. With the ignition on disconnect the light green wire from the sending unit and note which way the gauge needle goes. If it goes up past full, it is possible to add an adjustable resistor to the wire and trim the reading without purchasing a new gauge or sending unit. If the gauge goes down below empty that can't be done. I have been able to do that on other cars but have not tried it on a Jag yet.
If you don't want to do all of that and can wait, I have a jag that has that problem and I have intended to try it. So I will do the resistor test soon.
Let me know,
Howard
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QUESTION: Hi Howard,
I think your response may have been meant for a different person. The queries I have are in relation to the temperature gauge and a/c. Perhaps you sent my answer to someone else?
Frank
ANSWER: Hi Frank,
Sorry about that, I have brain fade at times and I have no idea what I told the other guy.
You are right about the temp. The ser III Xj-6 should show about 90 C. all the time. If all of the other gauges are readng correctly then the power to the gauge is probably ok. Jaguar does not use a voltage stableizer like other British cars. The temp sender unit is in the rail on top of the intake manifold. You do need to confirm that there is a ground strap from that rail to the engine at the rear of the manifold. Put your volt meter on a low volt scale and check to see if there is any voltage between the engine and the negative post of the battery. I found this to be a problem on several ser. III Jags. If you find voltage there correct the ground of engine to frame. If you find this you must right away get some anti electrolisis coolant additive for the cooling system. Available at truck supply stores. You would not believe what damage this can do.
Then you need to check the temp of the top of the radiator. Then check the temp of the coolant rail with all of the sensors in it. They should match and be in the 90 deg C. area.
I don't have specs on the ohms of the sending unit but I have two ser. III Jags and they both read correctly so I will ohm them and get the readings to you today or tomorrow.
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QUESTION: Thanks Howard for the very comprehensive and prompt response! Any chance of advice to the second query I had regarding a/c in my initial email? Thanks.
Regards
Frank
AnswerHi Frank,
I checked the ohms and it was cold at 63 deg F. and it was about 1K ohms and I warmed it up to about 88 deg C. on the gauge and the ohms went to 100 ohms. That should give you an idea of the range it runs.
As far as the AC goes you need to get the Jaguar manual as the system is very complex and it would take us a year via e-mail to trouble shoot the system.
Roughly the compressor runs all the time even with the heat on and it uses a series of vacuum operated doors to blend the correct temp from a sensor under the lip of the dash pad. Depending on the setting of the left control switch. The vacuum doors are controlled by a drum that opens and closes a bank of vacuum switches and a few electrical switches to control the two inside fans. The vacuum supply comes in a port in the lower right side fire wall and another exits the fire wall to operate the heater control valve.
I have worked on Jaguar since 1960 and I need the manual laid open to try to diagnosis an AC problem. It would take too much, too long to attempt to do it via e-mail. An AC man who knows Jag well may be able to do it but I know I can't, sorry.
If you are good with AC and electronics you could do it with the manual in front of you. If you get a manual and try it and need specs on an item, let me know as I have accumulated a lot data on specs from the factory that are not in the manual.
Howard
