A recent issue has started to develop with my 04 XJ8, for which I'm looking for possible causes. I've had the car since new, and it has had few issues to date. I'm at around ~65k miles.


Six times now while I have been driving along rural highways, I've had a "Restricted Performance" message pop up, the Yellow CEL comes on, and within the next 10-15 seconds, the temp gauge starts rising rather quickly towards max. In all situations, I've pulled off and shut off the car as the gauge approached the max, which is within about 30 seconds of the Restricted Performance message first appearing. I have waited about 5-10 seconds to restart the car, and on the first 4 occasions, the temp gauge shows at half way. On the last two occasions, the gauge immediately showed max with the Red light lit, so I shut down again and restarted right away and then the gauge showed half way. After all six occurrences, all seems normal, the temp gauge stays at the midway point, the restricted performance message is gone, but the CEL light remains lit. The first time this occurred, the CEL light went away after another couple days of short drives, and it was almost two months before the problem reappeared. The last 4 occurrences have been on successive trips, so it might be too soon for the light to reset on its own. I checked the coolant level, and it appears fine, and I have not had any coolant low messages.


The only other symptoms that might be related is that I notice when driving at highway speeds or on colder day recently, the temp gauge seems to come to settle at about the 5/16th point. Normally, once the car is warmed up, the computer managed gauge has always stuck at midway or just a smidge below halfway. Now it the gauge will only do so when idling at light, when driving around at slower speeds on warmer days, or for awhile after restarting the car after one of the 6 occurrences described above.


The battery is getting on in age, and certainly getting to a point where I should probably just replace it, but given these issues have generally occurred after driving the car for a bit, I'm not sure I see the connection to the battery in this case.


So, my questions are:

1. Is it possible to get a "Restricted Performance" message if the engine management computer thinks the coolant isn't warm enough?
2. Any clues what the root cause could be? Malfunctioning temp sensor; something wrong in the cooling system; Electrical issue?

The closest dealership is 60 miles away, so not overly handy to get to.


Thanks for any suggestions in advance.

 

Hey there I was on the fwy just a couple weeks ago and my instrument cluster coolant gauge went to max, just before I could get to a safe spot to pull over the restricted performance light came on and I lost power steering, etc. and car died. This in itself may not help you but the cause of this was later determined to be the bearing going out in the water pump.

When you pull over and turn off the car I assume you pop the hood and let it cool off or is there no signs of actual overheating, just a false reading saying its hot? I have a real time coolant gauge that gives exact temp readings that has been very helpful to me. If you get one it would tell you whether your gauge is throwing a false reading if the temp stays normal on the real time gauge. I believe mine is called "Scan gauge" and plugs into your OBDII port. It also reads codes.

Based on your description it doesn't sound like your car is actually overheating if you are able to turn car back on and have it be back at normal temp. If no overheating maybe a temp sensor however if it is over heating could be the thermostat on its last legs. Wait for someone more qualified to give their input, but it would be helpful to know whether or not the car exhibits signs of overheating besides the gauge climbing.

 

Interesting.


There is no indication that the car is really overheating. I am restarting the car within 30 seconds or so after the gauge starts its rapid climb to hot. And when restarted, the gauge is back to normal. There is no way the temp could change that much in such a short time. There is no smell or sign of coolant loss or cooking smells. But, given the nature of our engines, there is no way in heck I'm taking any chances.


In absence of any additional ideas, I think I'm going to proactively replace the battery which I realize is roughly 9 or 10 years old at this point. It has clearly lived far longer than it should have. If the symptoms appear to persist after the battery change, it looks like I may need to get the car up to the dealer.


Your situation leads me to believe that if the water pump or alternator is seizing, I could have similar problems. No issues with power steering though, so its probably not anything dragging on the belt.

 

Maybe read ECT with OBD to see what the sensor is saying. Then if it's very hot (as it sounds) you get to decide whether to replace it or trust it and then figure why it gets so hot (failing water pump or whatever).

I'd be scared of warped heads...

 

Given the fact that the temp guage comes down so fast, I dont think that it's over heating either. As you said it' pretty impossible for the coolant to cool down that fast. It may be time to replace the battery as preventive maintanance, but a dyeing battery would cause many other issues before yours. A going water pump or thermostat probally isn't you issue either as the car isnt really overheating. Most likely you have a lazy temp sensor. Although when my battery/alternator went bad, the cooling fans did run all the time, even when dead cold, and normal coolant temps. If the temp sensor was going it could send alot of bad info to the ECU. Put a live data reader on it before you start throwing parts and $$$ at it to solve the issue. The reader will show what the temp sensor is reading. Then a cheap infrared thermometer on the hose will confirm the real temp.

 

I replaced the battery today. On the short drive home, the temp gauge stayed pegged at a smidge below half way, which is where it should be. I won't have a better sense whether the battery fixed the issue until I can get it out on some of the highways to see how the gauge behaves. Until then, I don't trust the car, and we will use our other car for a road trip we have planned for next weekend. If it continues to act up, I will have to take it to the shop.

 

I just replaced the thermostat and housing due to a CEL which went off in my parking lot. Thermostat was DTC P0128 with no movement of temp gauge as I drove the four blocks to Jag independent shop. No restricted performance either. Just happened at right time for a change. Housing had to be replaced due to OEM and aftermarket thermostat not fitting. Must have been adapted for the plastic breakage in past ownership.

 

Thanks Jim. I've not had a need or time to take the car out for more driving replacing the battery, so it may take me a week or two to determine if the battery was the fix. If the battery did not solve the problem, I'm suspecting the alternator or the coolant pump/thermostat. If its the coolant pump/thermostat, I just can't understand how it could give low temp readings much of the time while driving at higher speeds, normal temp readings in city traffic or idling, and "fix" itself by merely restarting the car. In any event, I'm not willing to replace more parts on a whim unless the someone else can figure out what could be causing the strange symptoms.

 

Something like a broken piece of water pump might do it.

 

I've booked a visit to the dealership for Tuesday Mar 1st, as the temp gauge is definitely still running lower than it should (around 1/4 to 5/16th, rather than around 1/2). I will report back.

 

Tonight electric radiator fans running after engine turned off, first time this ever happened. I had never heard them before.

Later when driving 30 mph with air temp 65 degrees red lamp comes on next to temp symbol, temp gage right in the middle as always. After speeding up temp light goes out, and when parking electric fans again running furiously, engine running just a little rough and some surging when backing up, no smells or other sign engine is unusually hot.

Since the temp gage is in the middle and no other signs of hot engine it seems engine temp is normal, and a separate temp sensor is feeding false information to the computer which is kicking on the fans and giving a red lamp next to temp indicator.

Where is this sensor and how to check/replace it?

 

I would check your cooling system. Especially the water pump and thermostat housing, both areas prone for failure.

You definitely have an issue lurking and I don't think it's faulty information. Its an actual issue. And FYI don't rely on the temp indicator in the dash board... Many posts about it in the forms...

 

You were right abonano. Whilst driving to Galpin Jaguar the temp gage started rising and I was moving 5mph in Los Angeles highway traffic, so I had to put the heater on max and lower the windows, and the needle went back to the middle. That was a miserable drive.

Galpin found a cracked thermostat housing with a piece ingested by the water pump, and an oil leak from the pan (I hadn't noticed because it was dripping into the tray). Total including brake and power steering flush (whirring sound from steering wheel), oil, air filter, and accessory drive belt $2500.

Plastic thermostat housing and oil pan!!! These parts are subject to high heat and vibration and the engineers and executives who hired them must be idiots. Car is 10 years old but only 85k miles.

 

Glad you sorted it out before it was too late. The plastic on these cars is short of horrible. Unfortunately, there's no aluminum thermostat housing for the 03 plus models. I installed one on my 00 S Type. When I removed the original plastic housing it literally disintegrated upon touching it...

 

The shop diagnosed the problem to be a broken clips inside thermostat housing, which allowed the thermostat to be loose and coolant to flow past the thermostat.


This makes perfect sense, as I had become quite confident the thermostat must be sticking open, as that was the only thing that I could think of to explain why the temp gauge would rise so slowly and drop down so much when driving at highway speeds, yet come up to normal temps when idling for a bit. And my theory seemed further validated when I tried turning off the climate control a few times, and the temp gauge over the next few minutes would rise a bit (but still remained lower than it should).


If I understand what the service advisor was explaining on behalf of the technician, the broken clips also explain why the temp gauge would occasionally rise very quickly to hot. I'm still not understanding this part, unless the loose thermostat could temporarily block another opening that should not be blocked. And even so, I'm not sure how this could cause the gauge to rise from low to hot in a matter of <30 seconds, and show low again, upon restarting the car 10 seconds later. Does anyone have any further insight or theories into this?

 

Maybe the plastic thermostat housing should be changed at 80,000 mile intervals? Must be a lot cheaper than changing a water pump which my broken thermostat housing required.

 

The rental car they gave me was a few years old XF. Wow the styling and design has really slipped compared to my '06 XJ. My car is so much smoother, easier to operate, and to my eyes look so much more classier.

 

I'm not sure how this could cause the gauge to rise from low to hot in a matter of 30 seconds, and show low again, upon restarting the car 10 seconds later. Does anyone have any further insight or theories into this?

rhanky, I have a Ford pickup with similar symptom, and it is because there is a leak between a combustion chamber and coolant passage, which holds the thermostat closed until the water in the block boils and forces the thermo open.

 

XJPurr, Interesting issue you have in your Ford pickup. I should think that would be causing a host of other problems, such as one or more of the following: loss of coolant, fouling plugs, emissions issues, rough engine running, coolant in oil, poor compression, etc. In my case, I was not losing coolant and the car seemingly was running as smooth and strong as ever.


But that said, I still don't get how the reported loose t-stat in my case could on increasingly infrequent occasions all of a sudden cause the temp gauge to rise so quickly, and then immediately be back to mid to low temps upon restarting the car 10-15 seconds later. It kind of sounds like the loose t-stat would sometimes block something it shouldn't, and by shutting down the engine the lack of water flowing from the pump allowed it to fall back into place. I've tried googling for pictures of Jag thermostat housings, but they seem to vary wildly, and none really give me any clues as to what the various pipe connections are and what the t-stat could have obstructed to cause my problem. The loose t-stat seems to perfectly explain why the temp gauge was running cooler than it should, especially at highway speeds. I'm still looking for an explanation on the occasional rapid temp rises (which occurred moments after receiving a restricted performance message). Perhaps someone has a picture of the housing and t-stat for the X350's, and can annotate what each connection is for.


I'm obviously a little less enamored with these plastic thermostat housings & pumps than I was previously. Given the amount of labour hours it takes to replace the thermostat housing, it's not the sort of thing that most will want to pre-emptively replace. I'm not sure what the failure rates are, as on forums like these, we're only going to hear the bad news stories. My housing might have been compromised by me having the dealer pre-emptively replace the t-stat 3 years ago, which are known to fail in the closed position. Had I left well enough alone then, I might not have had the current issue.

 

It is a good idea to replace the thermostat housing, which includes the thermostat and seal, each time the coolant is renewed on the 4.2 litre engine.

The plastic parts are designed to endure a certain number of cooling and heating cycles and can eventually crack leading to catastrophic failure of the engine.

Typically, the thermostat seal fails leading to coolant being able to by pass the thermostat setting the DTC (P0128) and triggering the MIL. The coolant sensor measures the temperature sending a signal to the PCM that is compared to the length of time the engine has been running. If the coolant does not reach the correct temperature within the measured amount of time, the DTC is set and the MIL illuminated.