The oil pressure and temperature gauges in these cars are placebos. They go the neutral position quickly and will stay until extreme pressure or temp in your case is identified then the indicator will move. Chances are that you are reading it correctly by your other device but did not know about the indicator delay in the car. I can tell you that when your indicator begins to move to a danger point you need to react.

 

Thanks, Gus. I'll tell you one thing, when it did move off of mid-gauge, it went from half-way to pegged-out hot in about 5 seconds.

Gonna take the advice of the brain-trust here and replace the thermostat and the housing.

Cheers,

 

Well, I spent all day Saturday changing out the thermostat and housing on the XJ8. I have the skinned up knuckles and finger cramps that go with that operation, but it's done. I took the old t-stat apart and really could not see anything obviously wrong, but who knows? We've got another road trip planned in a couple of weeks, so we'll see what happens. I'm taking the trusty code reader with me this time.

By the way, here are a couple tips for anyone doing this job: 1) - Remove the air inlet pieces all the way to the intake manifold and you can get the entire t-stat housing off. I was trying to replace all but the neck piece, but I broke the flange on it while working the body off, so I had to get the neck off too. I've read that you have to take the manifold off, but that ain't so. Tip #2) - There are 4 screws that hold the housing to the engine block, one above and one below each of two flanges. When you reassemble everything, replace the two lower screws with two of the long double threaded screws that hold the old thermostat housing together. They are the same thread, and they will be a lot easier to get started because you have something to hang on to. It's also way easier to get a 13mm deep socket on a screw head you can't see than it is to hit the target with a torx bit. When you finally get those lower ones out, you'll understand what I'm talking about.

Thanks again for all the advice. I'll update after driving it a while.

 

Well folks, I just drove the Cat 300 miles with maybe half of that over 70mph and didn't have a hint of trouble. Think all is well now. Can't be 100% sure, but after seeing how that thermostat assembly is made, and knowing where the temp gauge sensor is located, I better understand how the problem was probably in that area.

Cheers,

 

I've been wondering about you, Larry. I was pretty confident you had it conquered, but glad to here it confirmed.

Cheers,

 

Great news Larry! Hopefully all the gremlins have moved on.
Thanks for the tips on replacing the complete housing too!

 

Kudos to you Larry! On the road again!

 

Thanks, guys. My main concern is that my wife and a girlfriend are taking the Cat on about a 2000 mile road trip later this summer, and I don't want them to have any trouble. My confidence level is a lot higher now. All I need to do now is buy a new relay for the air suspension compressor and show my wife how to replace it if she encounters the "nose down" gremlin. I figure that will at least get her back to civilization if there's a small leak or a sluggish compressor that causes the relay to poop out in the middle of nowhere. Happened to the same two ladies in the boonies of Wyoming last year, but the Select Edition warranty was still in effect, so it wasn't the disaster it could have been, albeit still a pain in the rear. Her girlfriend still rags on me for having "such a horribly unreliable car that can only be fixed by a dealer 200 miles away from wherever it breaks." Sigh - hopefully what she'll remember about this trip is how comfortable it was to have an X350 cradle her tush over 2000 miles of landscape.

Thanks again for the help.

 

Similar problem with a 2003 xjr...it was the thermostat...

So when you are done, take the thermostat and put it in a saucepan on the stove and see if it opens when the water gets hot. Mine did not, even at a full boil.

It was funny, because it did not always stick...sometimes, most of the time, it worked fine...

 

Yeah, anybody can design something that either works or doesn't. It take a really fiendish engineer to come up with a device that fails in a sporadic and upredictable fashion.

 

My wife was driving the 2004 XKR yesterday. Restricted performance came on at about 15 minutes into driving while going approximately 60mph. This is also when she noticed the CEL, temp gage pegged out along with red temp guage light. She pulled over, turned key off, then restarted. She had no problems driving the remaining 45 minutes home. I then pulled the p0116 code with a code reader.
I am aware the the temp gauge is placebo like, and that the restricted performance is automatic upon the P0116 code. My question is, based upon this P0116 code is it more than likely a stuck thermostat, or bad temp sensor, or something else should someone have had this exact experience? I haven't driven the XKR since, but will start again tomorrow.
I would have expected a stuck thermostat to stay stuck after an engine restart. I would also expect a bad sensor to be routinely bad....which may be the case as I drive it more. Anyone have this exact issue? Thanks.

 

First check your battery then check the temp probe and plug on the cross over pipe.

 

Actually, thermostats fail intermittently more often than not. Failure such that they stay open or closed happens less often. They are very cheap insurance in my book. I change 'em every three years or so.

You are also right about the gauge, basically it's an idiot light without the bulb. :-0 Ninety degrees Celsius to about 225 deg is "Normal", mid scale. Above that it shoots up the scale really fast.

Good luck!

 

I am certainly no expert, and I saw that the the problems were resolved on previous posts, but one thing no one mentions that is worth checking is a collapsing radiator hose. I had a Cadillac that would only overheat when driving on the highway at a consistent speed, and pulling over, shutting off the engine, then restarting would instantly cure the overheat. I thought it was a false reading. It kept doing this so i brought to my tech and she replaced the lower radiator hose and all was fine after that. The hose gets weak after many years, and with constant fluid flow like on the highway, the fluid flow creates a suction, and the hose would gradually collapse and then close off due to the internal suction, and then when the engine was turned off, the flow inside the hose stopped, and hose opened back up and coolant would flow again, nearly instantly bringing the temp at the coolant temp sensor back to normal. Just something to keep in mind.

 

Very good point! Proves how hard it is to think of everything and.......

Why this Forum is SO VALUABLE!


Keep it up everybody!

 

I drove the 2004 XKR yesterday and I couldn't duplicate the P0116 overheat condition as listed above. Since the weather was nice, I changed the thermostat (about $21 at Autozone). Total time was about 10 - 15 minutes. I simply unscrewed three T30 bolts (metal housing on 2004), about 1/2 gallon of anti-freeze fell into my drip pan, and swapped old and new thermostats out. Then tightened the 3 screws and filled reservoir with about 1/2 gallon of orange antifreeze.
While the old thermostat looked fine (I didn't test it), it was due for a change as I believe it is probably the original, hence that would make it 8 years old with 113K miles on it. The hoses all looked good, and I also cleaned the electrical connectors to the engine temperature sensor (which looks to be about $22 online). So hopefully this fixed the problem, otherwise I'll swap the sensor out next time should the P0116 show again, and I plan on doing a flush and refill in the fall anyways.
Thanks for the hoses comment, as I would not have considered that possibility; but that would explain the instant reset as well as an intermittently failing thermostat.

 

What sticks in my mind is that they got a code, RP & overheat indication pulled off the road turned the car off and then restarted and all was good. I do not believe a collapsed hose or a bad thermostat will clear the indications that quick. Although I do not know the time frame of the turn off and restart but based on what was written I believe a true overheating condition will take more time to clear.

I should also mention that that coolant system caps have a check valve incorporated in it to prevent collapsed hoses and enables the return of coolant from the tank. http://auto.howstuffworks.com/cooling-system7.htm

 

I know that sounds odd, but that is exactly how these sometimes act. I didn't believe it at first either, but it's been proven time and again. The same situation had occurred in the newer 4.2L if the outlet pipe that houses the thermostat fractures internally. Coolant just recycles in the engine instead of going through the thermostat to the radiator. Temp shoots up seemingly in the blink of an eye, shut it down for a couple of minutes and restart, might take it a while to happen again. Weird.

On the hose collapse thing, open your XK8's bonnet before you take off some morning, see if the top radiator hose isn't sucked shut. It usually is. If it isn't, I would want to check the pressure valves in the coolant tank cap.

Cheers,

 

For Gus:
The battery is basically brand new. The original battery lasted 7.5 years, until I started getting occasional window drops. It was then that I replaced it approximately 3-5 months ago. Also, the hoses seem true to their original shape and not soft anywhere.
I agree that a true overheat condition would not be rectified with an engine shut off followed by an immediate turn on. I do not believe I had a true engine overheat condition (I do believe the temp was too hot at the location of the sensor for a short moment). I believe that the P0116 code was triggered by a out of spec temp reading which of course caused the CEL, restricted performance, and placebo high engine temp & light). Keep in mind that the engine temperature sensor is several inches from the thermostat. Perhaps on this particular day the engine thermostat opened "late" (lets say at 195 degrees instead of 185 degrees) causing the out of spec reading for a moment until the thermostat opened.
When the car is restarted, if the engine temperature sensor is within range (which was probably already back in range during shutoff), there will be no restricted performance or high temp reading / light upon the restart. However, the CEL will still be illuminated for some time storing the previous P0116 code. This situation could also happen with a soft hose in which the hose is vacuumed toward being shut at a lower vacuum than before additional fluid is sucked from an overflow.
In both these cases, I can see how an immediate engine restart "fixes" the high temp reading / light along with the restricted performance. Additionally, it is quite clear earlier in this post or by googling, that others are able to "fix" their "reported" overheated engine condition by an immediate restart. So while these restarts "fix" restricted engine and temp gauge & light; there most likely was never a real engine overheat condition that ever existed (other than maybe briefly by the sensor).
In short, I believe that the placebo engine temp guage causes more confusion than help in these cases as an immediate engine restart would never bring the true temperature readings from "red" to "normal" by a quick turn of the key. Also, although I did change my thermostat, that may have nothing to do with the earlier P0116 my wife experience, or many not have even fixed that problem. If that P0116 rears its head again, I will update. Thanks all for comments and input.

 

I am open for good information and respect Steve (XJRGuy) who provides it, I have a great deal of respect for him. Bill I hope you continue to keep us up to date on your situation, I am anxious to see how this turns out. Thanks!