Spoof overheat condition. All models of V8 engine.

[J44EAG]

It is worth being aware of what can occur. I`ve seen this issue twice now on cars that have covered around 80k miles.

(These posts and thread has been later edited in the light of experience.)

What happens is this. There you are driving along, then suddenly the coolant temperature dash gauge shows a full red overheat condition! If this occurs, take the following action.

Stop the car and switch off as quickly as possible. Open the bonnet and place your hand on the header tank and engine. If the temperature is as normal and the engine is not blowing steam and coolant from every orifice, the chances are that your engine is NOT overheating. If that is the case, then probably all that has happened is that the coolant temperature sender has failed or the plug on connector has developed a corrosion resistance hot spot. Working the plug on and off the sender a few times may be all that is needed to restore normal function. On supercharged cars though, aged thermostats can also cause poor coolant flow around the engine and this can cause similar peculiar issues with spoof overheat conditions. Further explanation about this is in a later post.

The sender part number is AJ8 10031. My replacement has been ordered from British Parts and came for around £17 including P&P. Before ordering a sender though, be aware that thread size is important. Two sizes would appear to be available. Mine had a 12 x 1.25 thread but another I saw at a Main Dealer had a thread that appeared to be around 18mm. Obviously you need to get the right one for your car.

A good bit of advice here. BUY ONLY Jaguar original parts for these critical parts of your car. Namely temperature sender/sensors and thermostats. Several members including myself have bought cheap items which have frequently failed prematurely or not been up to the job even when brand new.

The sender lives adjacent to the water pump, and thermostat on the top front of the engine and is easily removable with a 19mm spanner. Screw the old one out, grab the seals off the old unit if not supplied with your replacement, then screw the new unit into its manifold location. Gently tighten, then reconnect the electrical plug. Top up coolant to the correct level and burp out any trapped air by squeezing the nearby hoses with the header tank coolant cap off and running the car up to temperature in order to have the thermostat open to expel further trapped air. Do this a couple of times after you have opened up the coolant system to ensure all air has been completely removed from the system.

Supercharged cars also have an auxiliary electric pump to feed coolant to the inter-cooler bricks. The pump is adjacent to the OS headlight unit and can be heard running when the ignition is on. The fuse for the pump is F31 in the engine compartment fuse box. Pulling that fuse should result in the pump no longer being heard to run. Similarly, if the fuse is intact and no sound is heard may be due to auxiliary pump problems or failure. This is not an unheard of issue.

You may need to clear any DTC faults from the power train electronic module. Either disconnect the battery for twenty minutes or clear the codes using a garage based diagnostic unit or a handy DIY unit such as the iCarsoft930i unit.

If you run any Jaguar V8 which has a mileage higher that 80k, I strongly suggest you buy in a new sensor and change before your car throws up this issue. I`m wise to this particular antic now on these cars. Forewarned is forearmed. This image shows a brand new after-market sensor which failed the grade when fitted to the car.

Mike

[J44EAG]

I`m still battling with this issue which has not been made any easier by the Xmas break and numerous commercial close downs over the period.

As a get me around measure, I installed a new but aftermarket sensor I had in stock whilst waiting for a genuine part to be sent down from British Parts. This has not been that successful in that the temperature gauge now fluctuates between stone cold and full hot! This really teases the engine management ECU which will within a few minutes switch on the restricted performance message, the orange lamp above it and the engine check light. a high idle can also become present. Clearing fault code off with my iCarsoft 930i helps but the orange light will often reappear. The temperature gauge will show cold but switching the engine off then on again will sometimes produce a full hot indication.

Clearly there is a fault still present so the next move is to await the British Parts sender, fit it and see what the result is.

To add to the misery, I ordered a genuine Jaguar part from Grange in Croydon yesterday afternoon which came down over night. I went to collect it and found the part supplied had a larger screw thread than the one I had removed! The sales guy let out a groan of despair which was louder than mine!!

So I`ve now returned to Portsmouth with the I930 plugged into the OBD port so that I could clear DTC codes as I drove back.

I`m hoping that fitting a new correct part when it arrives will be successful. In the meantime I need to be able to take my magnifying glass out to the car in order to read the small type face on the i930 a little more easily.

Paul has suggested there may also be a fault in the two wire cable or plug connector and that taking a resistor or two connected across the plug as a test measure might be helpful. I know the gauge seems quite active as it can move between full hot and stone cold deflections. I`ll add that the gauge will cycle up and down the scale between full hot and cold conditions so at this stage I`m not expecting a faulty gauge.

Not much more I can do until the new part arrives. The fun continues.

Mike

[J44EAG]

A call to Rob also produced a couple of other lines to pursue. Possible intercooler pump failure or blown fuse. The pump is located to the left of the OS headlight and may be accessed by radiator grill removal. Further research indicates the pump should run as soon as the ignition key is in the running position. Vibration from a running pump can be heard and felt when operating.

The second line of investigation is a partially failed thermostat. Rob has seen similar issues on his cars with similar results.

Further action today has been to buy a genuine new thermostat from Harwoods in Chichester for around £43 with JEC discount. I shall fit this tomorrow before buying a new pump, either genuine Jaguar (C2C6517) at a cost of £173 or perhaps fitting a higher flow Bosch replacement sold by chargecooler.co.uk who market up-rated components for tuned/modified cars. The cost for the Bosch pump is around £135 delivered.

Undoubtedly my supercharger mods and ECU up-rate will have caused an extra degree of strain to be placed on original OE parts which are now over eleven years old and have covered about 80k miles with no maintenance being done or being possible to coolant temperature sensor, thermostat or inter-cooler circulation pump.. That does not suprise me at all. If up-rates take place then other additional modifications often need to be fitted. My car now produces around 80hp more than a stock unit. The heat has to be got to be dispersed more quickly or performance and system reliability take a punch on the nose.

So tonight I once again have a full red temp gauge reading although the engine is running at a reasonable temperature, but the engine check light symbol and the orange MIL lamp get switched back on again after just a couple of minutes of driving time. The restricted performance legend also features on the dash message centre. The car is quite derivable with the engine itself at a normal operating temperature and no extra pressure being generated at the header tank cap.

We live and learn. A bit more spanner work and a few more quid should get this issue fixed. Something has failed and I need to find out what it is.

As I always say...when you are at the cutting edge of research and development, one expects to get a few troubles along the way. The secret is to accurately assess what the issues are, then fix them. Its just a question of elimination.

Mike

[ptjs1]

Mike,

As you know I'm very much against replacing any parts until I really know wherein lies the problem. Whilst a new thermostat may be good general maintenance, I'd really hold back from buying anything else, particularly a new water pump, until you've isolated the problem. Your gauge fluctuating to such extremes doesn't seem to my naive perspective to be a 'stat or water pump problem. I still think you've got a sensor, wiring or canbus problem.

I would start by using an IR thermometer to check the temp at the sensor head when the gauge suddenly reads hot or cold. Once that's isolated, I would then read the resistance that is coming off the sensor at that time. If the resistance reading is normal and at odds with where the gauge is now deflected, the problem would seem to lie upstream in the wiring or ecu.

I'd also be using your OBD11 reader to see the fault code that is being thrown and the real-time temp reading output from the ecu. All of this will help to narrow down the problem.

Just a suggestion - don't buy any more parts yet!!

Good luck

Paul

[J44EAG]

Out there again this morning with Dave Rex to try and sort this issue.

Turned the key in the ignition and the temperature gauge again went full red. Engine check light and orange MIL lamp still illuminated. Tried a couple of code clear downs which would put the check light out but the MIL lamp would light up again within a few seconds. Starting the car and trying that gave the same result. For some reason we couldn`t get any fault PO type codes off my Carsoft reader.

Rob suggested changing the thermostat for a genuine Jaguar item. (AJ8 6484) Not an easy job as one of the three Torx 6mm bolts is buried underneath the housing outlet pipe and access is not easy. I drained off a couple of litres of coolant before opening up the stat housing to avoid loosing it. The stat was replaced ensuring the bleed jiggle pin was in the 12 o`clock position and the three bolts replaced. This particular stat is applicable to MY02-05 X350 V8 models. Later models have a different thermostat.

We then moved onto checking out the supercharger inter-cooler auxiliary pump operation. The fuse for this is F31 in the engine bay fuse box. Details to be found in the owners handbook. This is a blue 15A blade type fuse which we all know so well. Turning the ignition on runs the pump at all times. With the fuse in place, the pump can be heard running to the left of the OS headlight unit. Pulling the fuse or switching the ignition off will kill pump operation. My pump appeared fully operational so no need to investigate further.

We refilled the coolant, started the engine an attempted further fault removal with the Carsoft. The temperature gauge remained full red. At that point we removed the aftermarket temperature sensor and replaced it with the old unit. Joy of all joys, the temperature gauge after engine warm up stabilised at the half way mark and Dave said the Carsoft indicated the temperature as being 87 degrees. That seemed about right for a just warmed up engine. Inter-cooler bricks were merely warm to the hand which indicated coolant flow through them produced by the auxiliary pump.

A quick code read and clear down left the dash in a normal state. A test drive of about five miles put the lights back on a couple of times but after the second clear down, the lamps HAVE NOT re-illuminated. Progress indeed. The test included a couple of big full throttle bursts down the dual carriage way without anything untoward reoccurring.

So where am I now? Seemingly the stat change may have helped get an improved flow generally around the engine. I don`t think the auxiliary pump operation ever had an issue but a question mark remains about both the old temperature sensor and the new item. Why the red hot gauge indication with both units? The old sender was in the circuit when the problem first came to light on the M26 on Monday. That was swapped out for an aftermarket new sensor that I had bought in as an emergency part to be kept in the car in case of original item failure. what on earth caused these faults?!

I`m inclined to think that the original sensor may have developed a plug contact hot spot. In addition, the thermostat may not have been all that it could have been after nearly 80k miles covered. Which caused the issue or was it a combination of a tired stat and a poor sender connection? To add more confusion having got the car settled in the car park, I had to clear faulting twice more before the car settled down on the test drive. Could that have been the ECU relearning parameters again after so much electronic mayhem had occurred?

So this afternoon I seem to have an operational car again. One does wonder though whether this issue will occur again soon. As always, time will tell. Here endeth yet another lesson in the mysteries of modern Jaguar electronics.

Comments appreciated.

Mike

[Zennan101]

Hi Mike,

Your systematic approach to problem solving always makes for a good read. I haven't the knowledge to offer any other suggestions but am curious as to why thoughout this whole saga you have never appeared to consider that the gauge may be giving a false reading?

Rod

[ptjs1]

Mike,

Well done. I still think you might have a fault in the sensor wiring which may well come back. Maybe just moving the wiring to change the sensor pushed it into an "ok" position. I can't see how even a faulty stat could cause those gauge fluctuations.

I would suggest you go on eBay and buy a £3 obdii plugin so you can read your engine codes. This would possibly have helped you at the outset. I'd also buy a few resistors from Maplins that equate to the cold and normal temp gauge positions. You can then use these to "set" the gauge temporarily if the problem returns.

Happy New Year!

Paul

[J44EAG]

A quick answer to Rods question. The answer is that the gauge is working seemingly as it should. Just been out there again and started with a cold engine. As it warmed up as I drove, the gauge moved up its range to the normal half way position and stayed consistent for my short trip. This has the original sender in the coolant manifold currently connected. I`m 99% certain the gauge is not at fault.

Paul. As we know sensors can be very fickle. Talking to Rob yesterday, he is emphatic that OEM quality is the only way to have it and considers it is only worth buying genuine Jaguar parts for this coolant installation. Jaguar themselves call the system "a precision coolant system" so if it is that critical then manufacturing tolerances need to be right on the button. Aftermarket products may not meet that quality. Rob also advised that in his experience that a new thermostat needs to be equally as well made. He went on to say that he had been advised by one of our Club tech guys that just changing the stat could make all the difference. Rob did just that and his problem disappeared. In this respect, I took his lead, advice and suggestions and changed my thermostat. That took one mechanical query out of the equation.

Almost definite now is that the Intermotor aftermarket sender is a duffer. Full red gauge readings. So the old unit put back in the car and better results obtained. However, this sender has done 80k miles and could have a weakness from use. What I now need is the new sensor which should arrive shortly. I can then do resistance readings for all three units in hot water at increasing temperatures and see how their graphs pan out as individual units.

Quite why my iCarsoft is not displaying code results is a mystery. I`ve set the car details into the unit and indeed it shows the correct Vin No. For some reason it will clear faults but not display what they are. It worked on my S-type well but not as good on this XJR.

I had a quick tinker just now with the ELM37 Bluetooth unit linked to my Android. It seemed to hook up quite nicely but as the car was not in restricted mode with either check light or MIL lamp on, it was not possible to generate a fault code on this occasion.

I am convinced that I may well of cleared a resistance hot spot on the sender plug and sender pins. It has been on and off now quite a few times. Having seen what I have over the last few days, I have it in mind that there may still be a sensor/sender weakness present rather than a CANBUS issue. Remember I`ve seen one of these sensor/sender issues before on my old V8 S-type and just changing the sensor cured the issue in moments and the problem was never seen again..

At this moment in time, what I need more than anything is a new sensor which should hopefully arrive early this coming week. A quality new part would appear to be what is needed and will take away the guess work.

I`ve also concidered the header tank probe which could have some gunk on it or perhaps have a dicky connection. It is mounted half way down the tank which would make tank removal necessary to access. I`ll take a look at that tomorrow.

Mike

[poprivet]

Hi Mike, top marks for both tenacity and documenting your adventures. Very useful information for many owners.

Temperature sensors have been an issue for many years, the early AJ6 needed a modified one to prevent overfuelling issues and some V12 owners are now experiencing problems, as engines become ever more complex fault finding is geting more difficult as faults are often thrown up in obscure areas.

It doesn't help when the technical information of the sensors is kept secret by manufacturers. There is an exact specification for every component such as the resistance / temperature relationship and should be very easy to test.

That said, I wouldn't be suprised if when you solve the problem it will turn out to be something quite unexpected like a poor earth or corroded electrical connection, maybe some lateral thinking is needed as well as logical thinking.

Keep at it buddy,
Al

[J44EAG]

Thanks Al. Happy New Year to you.

This morning I remained convinced that whatever was causing the faulting issues was indeed only likely to be one small thing...or perhaps two or three items that together combined to confuse and befuddle. I managed to provoke another check light and MIL light illumination and plugged in my Bluetooth ELM327 unit into the OBD connection. I opened up the Torque app on my Android phone and worked my way through the relatively easy diagnostic program. Lean on banks A &B came up. As Al suggested, some lateral thinking needed to be applied to why this should occur and what units were present on the car which might cause the faulting. I also considered what important senders were on the engine and their effect on the management ECU particularly on fuel mixture control. The pointer to the issue was the lean mixture thrown up on the diagnostic app.

The ECU takes its signals from the various senders or sensors on the engine. Most, if not all are sensors which adjust voltage output via internal two wire internal gubbins within the sensor which as in the case of the temperature sensor is an insulated "stand alone" from the metal ground status of the engine itself. Cleanliness of the connections is vital to ensure a decent low resistance value on the unit connector pins. Corrosion can wreak havoc and poor signalling to the ECU can take place. The ECU recognizes that something is out of limits and if bad enough can switch on the MIL lamp and/or the engine check light.

Crud on the internal parts of a sensor can also cause issues. For instance, you can often find a build up of crud on the header tank probe. That can cause silly difficult faults to be generated. Similarly it is not uncommon to find deposits on a temperature sensor probe. In my case however, the 80k mile sensor which is now fitted back to the car, appeared very clean indeed. Repeated connector plug removal and refitting may as Paul suggests may also have caused issues.

My deliberations lead me to consider what I had not yet cleaned up or inspected since I took ownership of the car in September 2015. The MAF sensor screamed out for cleaning and that as some of us know, does have an influence on fuel/air mixture control. Something I had meant to do but had not yet done.

Here is the hot wire before cleaning.

This type of unit will be found on many modern fuel injected cars. The MASS AIR FLOW sensor does just that. It senses the airflow mass through the induction pipe immediately after the air filter. It is well known that crud can build up on the hot wire and bulb and seriously upset the general running of a car engine. If crud is present, then signals to the ECU may go well out of acceptable limits and cause the engine to drop into restricted performance and switch on the MIL lamp and the engine check light.

Removal of the unit from the mounting tube immediately after the air filter is easy. Just two small Torx head self tapping screws into the air flow tube. Remove those and lift out the sensor. Pics here show that the filter face side of the hot wire was filthy with black gunge. I cleaned this off with alcohol panel wipe and a very soft paint brush. Normally I would have used spray carb cleaner but I had non to hand. Cleaned up, you can see the bright clean hot wire as it should be as in this image.

Fitted back to the car, I cleared the fault codes and drove the car. PERFECT with no further glitches coming to light. Hopefully I now have a permanent result. Again time will tell.

Right now I believe the MAF to have been out of limits due to being extremely dirty. I also suspect I had a poor connection to the temperature sensor or the sensor is somewhat tired. A sluggish old thermostat may also have had an impact on the general heat flow through the coolant system. The stat has been changed for a new item and although all appears well presently, the temperature sensor will be changed when a new one arrives hopefully tomorrow.

So that is were I am now with the car. Certainly a much improved vehicle than it was last Monday. Again, time will tell. I`ve learned a fair bit in the process of eliminating this run of faults.

Mike

[J44EAG]

Another update.

Last night the car faulted a further three times with the original temp sensor still on the car. On all three occasions this occurred about thirty seconds after start up. Cleared with Torque app and no further issues until another restart took place.

This morning, I started up and the car ran perfectly for the twenty minute trip!!!! No problem at all.

The delivery from British Parts is now due and should be here within the next hour or so. I just hope it contains the 12mm temperature sensor not the 18mm version!

Another update shortly.

Mike

[J44EAG]

And so this thread staggers on and on.....

Wrong part from British Parts delivered as AJ8 10031 although listed as correct for this April 04 manufactured car with the one piece thermostat kit (Later 05> cars have a multi piece thermostat and presumably this AJ8 100 31 sensor as part of that set up). British Parts came back to me saying that they had found another correct sized part as LNA 1600AA. In the meantime I had ordered LRA1600BA from XJK after a chat with them. Just under £30 delivered.

It is thought that LRA1600BA which I have seen before on a 4 litre V8 S-type is one and the same part as LNA1600AA as finally offered as the correct part by British Parts.

The intention now is to take delivery of the LRA1600EA from XJK and see if it works. BP will be receiving the AJ810031 back in return for a refund.

A good job I still have some patience remaining!

The moral of the story with these later 4.2 cars is to check the thread size of the temperature sensor if you have to change one and stress to your supplier that thread size is all important.

What a faff. Unbelievable that two Jag Main Dealers can only find one applicable part even when a correct Vin No has been given. There appears to be an um-notified cross over period when some X350 cars may have been fitted with the parts previously fitted to 4 litre S-types or XK8 models. What an irritant it is to find this changeover has not been built into Vin No records.

More again once the XJK sensor has arrived.

Mike

[ptjs1]

Mike,

LNA1600AA is an M12 fitting. This sensor is fitted to late V12 (x300), V8 N/A (XK8 & x308) and V8 S/C (XK8 & x308).

I don't know if it is an x350 fitting. I'll ask my parts man tomorrow. I'm sure he must be able to work it out from the part system!

I can't find any reference to an LRA1600AE part number. Are XJK sure that this is correct?

Paul

[J44EAG]

Thats as I understand it, Paul.

Help appreciated.

Presently the car is back to normal!!!

Mike

[J44EAG]

Continued minor faulting still present today which is happening as the engine reaches half warmed up, ie the first quarter segment on the gauge with the original suspect sensor still in place. iCarsoft unit is permanently rigged into the OBD port to clear the fault when it occurs. Once fully warm and the initial fault is cleared, the car appears to be ok until I switch off, come back to the car for say a return home, where upon the warm up fault starts all over again. Then it will clear for a couple of days completely until things go AWOL again!

XJK supplied me with the 4 litre 12.5mm temp sensor (LRA1600BA) which when fitted refused to let the car even start. So the old one back in yet again!

XJK who are jolly nice chaps are now supplying an LNA1600AA which they tell me is a sensor applicable to my Vin No of G33305. The info was apparently quite deeply buried. This should arrive early next week and I`ll try and clear the fault with this unit.

Later cars would appear to run the larger 14.5mm threaded sensor which is the commonly seen AJ8 10031.

Worth also noting that the MAF hot wire and bulb clean up together with a good clean of the plug and socket appears t have given the car a noticeable increase in low speed torque and more reliable and spiritly get away from a standing start. Those having followed my posts since I squired this car might recall I have always had a groan about lack of low speed grunt. The MAF sensor cleanliness issue appears to be extremely important in keeping these cars running well. We live and learn.

More news in due course.

Mike