My 1998 XK8 convertible has real gauges installed. Typically the temp will stabilize a little over half scale when warmed up. The oil pressure will start a little over half scale when cold then drop not quite to red line at idle after running for awhile. The pressure will go back to about half scale when the car starts moving again. This has been consistent for some time. Coolant and oil levels are both OK. Recently I noticed the temp and oil pressure both climbing to about 3/4 scale when driving. The oil will still drop to almost red line when idling , but then reads higher than normal when driving again. The temp seems to climb slightly higher at idle and then drops back to about 3/4 scale when driving again. Both fans are running. I'm assuming the oil pressure and temperature are related, but I don't know what to check. The car seems to run fine while this is happening. Hoping for suggestions.

Thanks

 

I think you are over reacting to the real world, but the fans running does bother me. The low speed fan should come on at about 205 F and the high speed 210. Once you are moving the fans should be off unless the A/C is on. When the A/C is on the fans will be at high speed.
If the fans are on without the A/C the thermostat may not be opening correctly. Your observations are appreciated and may just indicate why the factory made the gauges read 'good' through a wide range.
If you could connect a code reader that can show real time data the temperature readings in degrees would be more informative.

 

here is some information that may be helpful in your diagnosis.

as pointed out, a permanent full time readout from the OBD-II port would be useful as far as assigning temperature numbers to the oil temperature and coolant temperature. I use the (low cost) Autool X-60 gauge, sourced thru Amazon. I have it placed on the left hand corner of the dash. Very unobtrusive and out of the usual road view line-of-sight.

It can be easily programmed to display many different engine & transmission data points in either Centigrade or Fahrenheit scales.

I usually keep mine displaying the engine coolant and oil temperatures, as well the trim data.

Z

 

Z ray ..I use the Scangauge reads similar to the X60 but I did not think there was an oil temp sensor in the engine (97 4 L) hence for real gauge you have to fit one....can you clarify on this as I cannot get an oil temp reading.
I think you are right about the varying oil pressure readings particularly as the idle is very low at 600rpm and the oil pump mounted on the crankshaft.

 

Oil pressure is a switch (hence why Real Gauge needs to plumb in an extra sensor), oil temperature as standard is a thermistor which gives the actual temperature. Whether that is true all the way back to the 1997 model you will have to check. See the Oil Temperature Sensor thread.

https://www.jaguarforums.com/forum/x...1/#post1025807


Attachment 91900

 

Thanks for that .am changing the alternator so will be in that area ..have seen your diagram .
If the oil temp controls the VVT perhaps I must have one ....

 

Sorry, I’m not knowledgeable enough on the early 4.0 l cars to know about an oil temp inclusion. The ‘02 models have them, that’s all I can say with certainty.


Z

 

Fitted from the get-go, according to JEPC:



It's the same as the coolant sensor on 99-up 4.0L XK8, and fitted to the replacement crossover pipe AJ85885

 

I just got a new oil pressure switch and its marked 0.45 Bar thats about 7 LB PSI so if the oil light is off you must have over 7 psi probably in the 10-15 range at idle.
I dont know what sort of oil pressure sensor you fitted but all the electrical ones are very inaccurate so dont worry.
Observe what is your Normal .

 

I have two inexpensive OBD readers. They both showed the coolant temp maxing out about 205 F. Neither would read oil temp or pressure. One said the car didn't report them. For what it's worth the OBD readers speed both showed about 3 MPH slower than the speedometer. The speedometer matched my phone GPS speed. I have not tried to match the OBD coolant temp to when the fans kick on or off. I asked TheJagWrangler if something like a bad ground could cause the change in both gauges. The following information on RealGauge is from TheJagWrangler:"Coolant temperature is normal up to about 220 F (just a bit over the 3/4 point), though it should only briefly peak this hot until the fans kick in. I have never seen a failure mode like you described with both gauges malfunctioning by an equivalent amount. However, if you want to reset the gauges, disconnect the negative battery terminal for 10 seconds and then reconnect it. That will reinitialize all of the electronics."

I did the reset with no change. At this point I will just monitor the coolant temp and oil pressure closely since the consensus seems to be I don't have a problem. I still have to wonder why after years of driving this car the indications both jumped from their previous stabilized readings.

Thanks