This problem is baffling everyone who has looked into it; the car is a 2005 XKR 4.2.

The car performs perfectly normally then, occasionally when in heavy traffic and on a hot day, it will overheat. The aircon goes warm and the temp gauge goes to red. When it is not possible to stop straight away turning on the heater to full brings the temperature back down but when it is possible to stop I have noticed the fans are NOT working, then will cut in when the engine is shut off and then they run for ages. They will stop if the engine is started again which is logical as they will have reduced the water temp in the rads which then flows to the engine sensors. This does not happen every time it is in hot, heavy traffic, just occasionally. Recently it happened after about 10 mins in traffic then later the same day the car performed perfectly normally in far worse traffic for a good 30 mins. I have changed the thermostat and its housing, the main water pump and the auxiliary pump to the supercharger and it has not cured the problem.

My untrained logic suggests to me that there is a problem with the fan not coming on when the engine gets too hot from lack of airflow through the rad but I am now being told by a Jag main agent, that the problem is blocked rad’s, both the main and intercooler, which is illogical as if they were blocked I would have thought the car would constantly overheat. Also the car has only done 55k miles which looks to be a bit light for both rad’s to block. They are also saying the water temp coming out the rad is higher than it going in, which again sounds illogical to me. They have decided on the problem and now simply discount anything else as being possible, mark you it was the same people who diagnosed the two pumps as the problem a year and £1400 ago! I have had the car looked at by a non-Jag garage and they are stumped as well.

Before I splash out a fortune on new rad’s I was hoping someone on here might have some other, more logical, suggestions. What controls the fans operation? Is it a switch connected to one or more of the coolant temp sensors or is it through the ECU? Is there any likelihood of the ECU being the trouble? Could the problem simply be one or more of the temp sensors playing up?Any help would be most gratefully appreciated.

 

You are perilously close to writing the engine off

Hopefully it is not too late.

Clearly the fans should have been on so someone needs to fix that but do not let the temp get so high or it may in effect write the car off.

 

^^+1
Please don't use the car in anger until someone who has a clue (highly unlikely the dealership will) finds the cause.

Dealer will likely just keep throwing parts at it until either (i) someone accidentally hits the right part or (ii) your motor seizes.

The fans in the later MYs are variable speed, but I believe they should be running when the A/C is switched on. Someone will correct me if I'm wrong here.

 

Before doing anything else, have the codes read. Use the result as a guide.

Fans are controlled by the ECU, on a continuous basis (PWM). This is not a simple off/low/high setup.

Do a simple check: turn the A/C on and check the fans are running. Both run together, AFAIK, left and right are not controlled separately.

When they did the cooling system work, did they accidentally mix coolant type? This car needs DEXCOOL. Mixing incompatible types can lead to gelling and clogging of the system.

Best of luck, keep us posted.

 

Thanks fmertz.

I have no idea re coolant but will get it checked. The car is going to a specialist (not Jag) on Thursday so will pass all this on to him.

I am well aware of the danger to the engine if it gets too hot but the problem only happens perhaps once or twice a year! The last set of parts were supposed to have fixed it, hence me driving the stupid thing since July of last year with no problems until a week or so ago. Hitting the heater immediately reduces the temperature.

Will let you know what comes out of this weeks investigations but do you think a faulty temp sensor could be intermittently failing to give the ECU a 'start fan' signal?

 

I recently diagnosed an overheating problem on my XK8.

Step 1 is: Make sure to monitor your temperatures through an ELM 327 dash panel or equivalent as the temperature gauge in your car (at least the older cars) is wildly inaccurate. The diagnostic reader will let you (or the diagnostician) know when to shut down the car.

2) Measurement in hand, the easiest / cheapest solution would be to replace the thermostat.

3) If you are indeed having problems with the fans.... (Watch them in a good light. At least in the older car, they are surprisingly tricky to see if they are working properly in poor light.) look to the temperature sensor in your car. Again, I know that my experience with the old NA car may differ from yours....If the sensor is in the top cooling tower structure, it is likely that the part is inexpensive and easily replaced. (Easier than the thermostat in fact !)

4) Have the radiator flushed or do it yourself (warning: kind of messy).

Assuming the problem is not the unthinkable (engine difficulties) diagnosing cooling problems, in my recent experience, was fairly straightforward. But please keep an eye on the temperatures with an accurate digital gauge.

 

Jaguar cooling systems are High Velocity, Low Volume design. If you have a higher temp OUT than IN then you have a flow problem.

First start the vehicle from cold engine, then use the climate control to take the A/C to max output. The fans should come on and with the bonnet open you should feel a HIGH volume of air flow. That would indicate the fans are working.
Shut the engine off and then let it gain cool to a cold start condition. Then turn the ignition key to the on position, but don't start then check by ear or feel to see if the supercharger coolant pump is working. You should be able to hear it or touch and feel it running. If it isn't then then the condition needs to be repaired. A bad supercharger coolant pump will allow the engine the develop " heat soak" and cause temperature problems.

If the pump is working and then I would recommend having the radiator and the inter coolers cleaned by a radiator repair shop.

 

FWIW, the cold side of the radiator is on the driver side. You can tell because this is where the transmission oil cooler lines are.

Did you replace the thermostat and housing as a unit? The Jaguar part is not that expensive ($100?) and includes all the gaskets/o-rings AND a new sensor, all pre-assembled. If you replaced the thermostat alone, there is an off chance it can be put in incorrectly I believe and cause problems.

Again, check the codes, chances are the car is trying to tell you something. If the gauge is up, then the sensor is working. Chances are, it is trying to run the fans, but somehow cannot. Clearly the fan motors work, and the fuses are fine. Maybe you need a new controller (mounted on the shroud). Again, I believe the ECU can figure this out and throw a code (which may or may not trigger a light). You can look up ELM327 for a cheap device (eBay/Amazon) to pair up with a phone app.

 

Thank you all.

I have printed all your suggestions and comments and will pass them on to the engineer and fmertz thanks for the heads up re the shroud mounted controller, that's the first place I will get checked out.

To answer questions posed. The supercharger water pump was changed last July so is effectively brand new, the old one was only working in fits and starts. The thermostat housing was changed when the new thermostat was installed, again July last year.

Looks like its going to be a messy couple of days with rad coolant going all over the floor!!

All the best.

 

Ross

I had exactly the same symptoms on my Audi A6 quattro, it turned out to be a wiring loom break in the harness, but it could easily have been the control unit between the fans.

Am not sure if your 2005 has anything like this?

https://www.ebay.co.uk/itm/RADIATOR-...sAAOSwuwNZjMJg

Good luck

 

Thanks MarkyUK.

No, mine is a later model and that part was not used on it but thanks anyway.

I have discovered the control module for the fan unit does not come as a separate part, it only comes in the entire fan unit at £522!!! What a poor design for us poor drivers, Jag are laughing all the way to the bank!

 

Cheap to buy used.

 

You might want to double check first. Taking the shroud off is a (minor) pain, but can be done without draining the fluid. It comes off with the fans and controller attached. Check and re-secure all the plugs. Use electronics contact cleaner. Check for corrosion. If that expensive new, you can either locate a used unit, or find an electronics (ECU?) repair place that could possibly repair it.

I would start with the easy stuff, check the plugs on the left side of the radiator (heavy gauge for the power, separate for control), check (and even just replace) the (cheap) relays involved.

Sorry to bring this up again, but check the codes. From memory, I started the car one time with the fans disconnected as part of a radiator replacement, and it resulted in a code. Don't commit to spending that much without firming the diagnostics, as a general rule.

 

Morning all.

First up-date.

I looks as though the Jag garage may have been right re the main rad. We have used an infrared thermometer on it and the water coolant is indeed coming out hotter than its going in and there are hot spots in the rad so its coming off and being back flushed to see what junk comes out. When done the heat test will be repeated and if the same results are seen the rad will be changed. The intercooler is working fine so Jag were possibly only 50% right!

Re used fan units: I have scoured the net and can only find 2, both in the USA, I'm in the UK. One has no electrics or control module. By the way there are NO codes coming up at all.

 

Being that I have worked at a dealership for 21years and just throw parts at cars I will pass on a little info. Are YOU SURE the car is even overheating? On my 04 XJ same setup it occasionally will go into the red, and shut off the ac with cans going on high. IT IS NOT OVERHEATING! But the ecu thinks it is. I have a intermittent CAN network failure and looses signal. Not always are issues what they seem, the fact that its very intermittent leads me to believe you may not be overheating. and also check for air flow when the fan is on as they are pulse width driven so it may not be coming up to speed

 

I had the very same symptoms on my 06 XKR, the ac would go hot at stops and the system would go in the red. It was a failed fan control module. It is in a pocket on the shroud. I got one from Coventry West and have had no more problems. I did find that there was tremendous debris between the intercooler radiator and the ac radiator. It took awhile to wash it clear.

 

Thanks Brutal but the thing is 100% overheating, the air out of the offside vent is hot enough to cook eggs when the fan decides to start blowing. Also thanks to oldmots, I thought it might be the fan module too, I will see if Coventry West a0 have a module and b) will ship it to the UK where I am based.

 

Hi All.

Another update on my poor old XKR.

All three rads showed signs of leaking so they have all been replaced. I found a company in Scotland who supply a double thickness supercharger intercooler at less than half the price Jag want for the standard one. All looked fine and the car was driven hard to get it hot, hot then left to stand idling for an hour in the UK's unusual heatwave (27c). The temp did not go above the halfway mark at any time, just under in fact thanks to the larger intercooler, the fans cut in and out as they should and I was about to collect the car when the header tank burst at it's seam! It was 13 years old and has obviously been overheated when I had the original problem, several times, so I'm not too worried but just in case a cylinder head gasket is failing and over pressurizing the system I am adding Steel Seal to the water system. This worked a treat on my XJR when I blew the off bank cylinder head gasket some 6000 miles ago, its been fine ever since.

Looks as if Jag were right in the first place! Need to eat some humble pie next time I see them.