so im driving home...notice my temp gauge is in the red...with red light on ...I pull over and put the heater on full blast which makes the temp go down back to middle where its supposed to be.

I start the car again...temp is ok for a while ...then oil pressure light comes back on and temp goes right back up to red area and red light comes on.

I shut it off again ...took a look at the engine...it was warm as hell...no leak but fan kept running even with engine off...

I let it cool down for five ten minutes...then started up and drove home with no more issues...

besides the gauges no issues ...running ok ...no other symptoms ???

Oil pressure switch ?? Thermostat ??

any ideas guys

 

Thermostat is the most likely, but with temp that high, you have probably destroyed the water pump impeller. They disintegrate under high temps. Neither one of these issues would be related to the oil light. The fan and gauge temp sensors are independent, I'm amazed you actually saw the gauge go up, most of the time the sensor doesn't pick up the temp. Check your oil level.

 

Do you have any facts to back-up your WP comment?
Do you know what is the temperature service range of the material for the impellers?
As for the gauge, I disagree 100% with you. it is a know fact that the gauge work but not in a linear way. Anything above a certain temperature will show the needle moving from the middle/normal position

 

If you have no coolant leaks, you probably have a bad thermostat and possibly a bad water pump. Do not drive the car until this is resolved. The needle will be centered from about 185 F to 235 F. Above 235 F (overheating) it rises to red.

The viscosity of the oil decreases with temperature. Very low viscosity oil will result in lower pressures, especially at idle, which could be the reason for the oil pressure warning at overheating temperatures.

Once the overheating is resolved, change the oil. The excessive heat accelerates oil breakdown.

 

And... For the less mechanically inclined among us, it is a very risky strategy to "let it cool down" then drive it home, without identifying the root cause of the overheating event. It is risky in a Ford, Chevy or any other car, but especially in an aluminum blocked car with a high performance engine design. When an overheat even seems to occur, as a minimum, check the coolant level, if it is low, and you have no coolant, put clean water in. Make sure the coolant level stays high and is not leaking, then make sure the coolant is circulating by carefully feeling the top radiator hose to see if it gets hot (abouy 200 degrees). If not, walk and call the flatbed.

 

So I cranked up the heat in the car and let it cool down with the engine off but key in the ON position...the needle came down right away...

I do agree that driving an overheated car is dangerous ...but i felt it was safe with the temp back down to normal.

Anyhow I took the car back out yesterday evening to see if it would do it again...

no overheat ...no oil pressure light...we will see how this plays out

 

Replace your thermostat. It is not uncommon for them to stick intermittently. It is cheap insurance.

 

Suggest you invest in a RealGauge for your XJR so at least you have a temperature gauge you can trust.

 

Thats exactly what I was thinking and my Jag mechanic said thats probably it.

Im going to search the forum ....think its an easy job...Will do it myself...

anybody do this job themselves ? Easy ?

 

Yes, I have 9 years experience as a Jaguar technician. I have changed water pumps left and right from overheated cars. Second, with a bad water pump, the gauge moves. FREQUENTLY the gauge does not read as overheating when the thermostat is stuck closed, but the fans go to high speed, indicating the overheating. Not sure I like your attitude much Luc.

 

I bought a low temp thermostat from eurotoyz ...will replace it and report how it goes

 

Changing WP on overheated cars do not mean that the overheating damaged the impellers.
As a matter of fact too many Jaguar techs replace perfectly good water pumps after overheating and Jaguar had to issue a TSB (308-60) on this subject and the only impellers susceptible to damage was the back Nylon 66 on earlier cars.

 

A water pump and thermostat are cheap insurance. Tow it home if you have a problem.
I got stuck in traffic and pulled over as soon as I could safely and it still damaged my engine.

 

I was lucky. My Thermostat stuck OPEN.

 

I doubt the value of a real gauge for someone who drives the car home after it overheats. And I don't like your attitude much either, Margate.

 

someone recently made the comment that: " FREQUENTLY the gauge does not read as overheating when the thermostat is stuck closed, but the fans go to high speed, indicating the overheating."
Every cars or trucks that I have ever worked on, including my 01 XJR have the sensors for both ( when needed) the water temperature gauge and engine computer BEFORE the thermostat,
In such a design, I fail to see how a stuck closed thermostat could have any impact on the sensor being able to read temperature.
As a matter of fact, a working thermostat is always closed until it's rated temperature and the temperature gauge has no problem showing the coolant temperature before opening.
The only time that a sensor will fail to read temperature is when the coolant level is so low that the sensor is not immerged in coolant/water

 

Agreed, just suggesting it as a path forward modification so he actually knows how hot the engine is getting in the future.

 

The reason the Jag guys did what they did is because people obsess over silly stuff. An engine is designed to run at a range of temperatures. The Jag supplied gauge does indicate temperatures over the normal operating range, and if you stop and take action when your gauge indicates above normal temperature, you will be fine. My MY 02 car has been overtemp twice (jammed fan at idle and blown hose), and indicated such, and we stopped and then analyzed and fixed the problem. It still purrs a hundred thousand miles or so later. I run an OBD scanner and monitor temp in my XJR, but the average XJ8 owner has no real us for an auxiliary temperature gauge except for what I use mine for which is operator entertainment!

 

Hi Spark, Im not sure if im reading your post right but you seem to be taking a shot at me for driving the car home after my car overheated.

Im going to repeat myself, I noticed the temp raising right away and pulled over right away. I cooled down the engine by cranking the heat to the max which returned the temp to normal almost immediately.

Then when I started the car again the temp was normal.

At that point I was literally half a mile from my home and drove it home at the normal operating temp...not with the needle in the red.

I remember this forum being a lot friendlier....

 

Well, I would not call it a "shot", but I will say that running a hot car until the "oil pressure" light comes on is usually a very bad idea. Unless you are in a place where stopping was dangerous to your well being, (in which case the cost of the car is immaterial), then the correct distance to drive is just out of the lane of travel. In retrospect, I guess the light that came on was for overtemperature, not actual loss of oil pressure, so you are probably OK.
By the way, as to your question about the thermostat. You probably want to change the riser that it mounts in to a metal version while you are at it. The plastic ones are known to crack and leak. Before you change it, have a look at the archives for the advise to brake the old riser off with some pliers for access to the mounting bolts, then go back with socket head cap screws in place of the hex bolts- using a "ball end" allen wrench socket. Be sure to look at the old thermostat as you remove it so it is clear which side faces "in" and make sure the little "weep" hole is oriented to the correct upward location.

But I stand by my original statement: It is RISKY to drive a car with an aluminum block engine any when there is a temperature issue, 1/2 mile, 2500 feet or whatever, it can lead to a major engine event. And an auxiliary temperature gauge would not have changed anything about your experience either , would it?