I have a 1999 xk8 I have replaced all cooling components other than the radiator.When on the road temp remains at approx 200 deg, when i stop at lights jumps to about 210 deg this is confirmed by real gauge. The fans are running, then returns to around 200 deg when driving. After 16 years would it be wise to finally upgrade and change the radiator.

 

I've moved your post from the General Tech section to the XK8/XKR section where you will get better response.


regards,
Steve

 

Long discussion on this subject here: https://www.jaguarforums.com/forum/x...rature-138312/

I had this question when a new radiator cross over pipe with its accompanying temperature sensor kept the fans running with the AC off in 20*F weather. Buried in there is the resistance values of the sensor vs coolant temp. At the 190* area, while not exactly linear, 30 ohms equates to about 20*F. Remember the RealGauge, which I have installed also, is only displaying the ECM's digital interpretation of the resistance value of the sensor in ohms. Once you are comfortable with the real engine temperature as measured by an outside device such as the IR gauge you can calibrate the RealGauge to that value.

My solution was the third new temp sensor which was the closest to the Jaguar specifications which are contained in the above link.

Bottom line is that my OBDII port reading and correspondingly the RealGauge read above 200*F in normal operation. That is while the IR gauge reads 180*F on the brass temp sensor and 206*F on the head itself.

It is just not right that with a 183*F thermostat the OBDII port reads at the boiling point.

 

Thanks Test point. Gauge and scanner read the same temp , Im pretty good hands on with tools not so good on under standing the electrics. Is the temp sender the culprit,

 

You are going to have to invest in an IR gauge or find someone that has one to confirm the REAL temperature of the engine. Measuring the resistance of the sensor only tells you what the varistor thinks it sees.

After my experience I was left with two impressions:

Jaguar has never published what the expected running temperature of the engine should be. The closest information is the expected resistance of the sensor. I have had cooling problems in the '82 Volvo referenced below that turned out to be a 32 year old radiator and the engine head temperature is only 3-6*F above the 180* thermostat specification. Not so on the Jaguar.

The manufacturing resistance tolerances for the temp sensor is outside of what I would consider reasonable. It took 3 sensors to find one that sorta displayed an approximation of the expected temperature and that only ran the fans when the temperature was above 20*F.

Another thought: With the idiot gauge on these cars someone could leave the dealer after a complete coolant system rebuild totally unaware that the engine is running hot and that the fans are running all the time.

 

Thanks again Testpoint for your info, I have a if scanner i will get a reading at temp sensor .Fans don,t run all the time i will try and see what temp starts them running. What puzzled me was the sudden jump in temp when stopped at lights, I thought with fans running temp would stay about the same. Thanks again for your help.

 

Infrared Thermometer - Non-contact, Digital Thermometer

 

I have one. got it to do trans service .will check it out tomorrow. Thanks walter.

 

Reading the OBD II output on a ScanGuage my 03 XK8 runs around 190 to 196 at speed, it will climb as high as 209 when stopped or slow moving traffic.

 

Have you any idea the temp when fans should come on, so i can check mine tomorrow. thanks walter.

 

This info is buried in the above referenced link. It is not identified if this an external device measurement of the coolant temperature or a reading at the OBDII Data Port.
. . . . . . . . . . . . . ON . . . . . . . . . . . . OFF
Slow (Series) . . . 90*C (194*F) . . . . . 86*C (187*F)
Fast (Parallel). . . 97.5*C (207.5*F) . . .93.5*C (200.5*F)

Keep in mind that the gauge or scan tool reading has only a varistor resistance translation to the real coolant, or head temp.

 

I have had the Real Gauge since it first became availalbe. My coolant temp showing on the dash was consistently very slightly - if even noticeable - above the midpoint on the scale, about half a needles width above midpoint, during normal steady cruising even mid summer in Florida. I have that as the baseline in my head. Recently (at about the same time as your posts on this started Tespoint) I too replaced the crossover, thermostat, and sending unit with genuine Jaguar parts, and ever since, the needle sits consistently slightly higher on the gauge, about half a notch higher, than it used too. It bothers me that it isn't where it was/should be. I don't notice my fans running more frequently or sooner. I will pick up an infra red temp reader, but because Realgauge was showing proper temps for more than a year, and immediately after the new parts it shows higher, I am sure the engine temps are the same as ever, and are normal. I read your other post about this, and then re-read the Realgauge instructions, but didn't see how to calibrate it to compensate for the unacceptable tolerances in the sending unit. Testpoint or Steve, can you point us to the actual calibration procedure? Is it not advisable to re-calibrate the Realgauge to compensate for the sending unit?

 

I hesitate to change the RealGauge calibration at this point. The thought is that I will wait until a little later in the Summer to see how it displays then. I would prefer it to alarm a little sooner than later.

 

Test point looked at car again this morning, ran it up to temp , both fans came on at around 204 degs they seemed to be running high speed. temp dropped and they both switched off at about 197 degs , did not get any slow speed at 194 degs that is if my scanner is correct. Is there different relays for slow and high appreciate your help in this matter.

 

Also tried a reading on thermostat housing but was getting slightly lower reading than what my scanner was giving me about 5 to 10 deg difference.

 

My IR readings on the brass temp sensor are all in line with what I would expect from the thermostat specification, not the resistance value of the sensor varistor. About your 10 degrees.

The bottom line, in my opinion, is that he Jaguar specified sensor is not within the resistance specifications specified by Jaguar . . . but the failure is in the right direction. A brand new sensor provided in the cross over pipe measured 30 ohms below Jaguar specifications, 10*C/20*F more than the Jaguar specifications. The over temp light will come on at a lower temperature than the actual, real, measured by an external device coolant temperature.

A replacement brand got closer but is still causing the 5*C/10*F higher than expected reading.

 

just ran a test sitting in my driveway. Temp readings from my Scan Gauge connected to the OBD port

Factory temp gauge hit mid mark at 184 and stayed there.

Thermostatic appeared to open at 185 as the lower hose started to get warm, temp dropped to 182 and went back up.

Both fans came on at low speed at 193 and the temp stayed at 193 for 10 minutes while I watched it. Never got any hotter idling so I shut it off.

 

Sounds like your car is perfectly matched to the Jaguar specifications. Mine is not.

Original temperature sensor?

 

I want to thank Test point And Jandreu for your input , I now believe my readings are showing higher than they should. New cross over pipe with sensor was installed about 3 months ago just before i fitted the real guages. I suppose it is better to show higher than lower, I would just like to get it right. I have spent 2 years rebuilding the car from the ground up drives like a dream, Thanks again Walter.

 

Just an FYI from JTIS