Hi All,
I've been enjoying driving my XJR to work for a few weeks after being off the road for months. Just as confidence was restored, last night I went outside about 45 minutes or more after I got home to water some plants and noticed that the radiator fans were still running, even though by this time the car didn't feel that hot when I opened the hood.
Worried that something was wrong and I could end up with a flat battery, checked the hand book and removed F17 cooling fans (parallel). they kept running, so I replaced that fuse and removed F11 cooling fans (series/parallel), that stopped the fans (both in left hand engine bay fuse box).
I started the engine and ran it back up to temperature on the drive. It seemed to hold at the normal position on the left edge of the 'N' on the gauge.
So I set off for work this morning with the F11 removed. Temperature fine despite some unexpected heavy traffic until on one occasion the temperature started to rise. I pulled over, refitted the fuse, and the fans started, quickly pulling the water temp down and I continued my journey. The odd thing was that now the gauge settled in the middle of the 'N'. Once at work I removed the fuse so as not to end up with a flat battery if the fans didn't stop.
After ~3 hours i replaced the fuse and the fans didn't start, which would seem correct as the car was now near enough fully cool.

Do you know how long the fans should realistically run for?
I've had the car 14 years and thought they only stayed on for a few minutes after turning off. never noticed them still running after 45 minutes.
Any ideas on what could be wrong, or given that the fans are now stopped with the fuse in, could the system be working correctly and just have been hot last night due to fast run followed by slow traffic and relatively hot weather (22 C)?

Any comment welcome!

John

 

It's probably a faulty relay. Did you check if you have enough coolant?

 

The white coloerd fan control relay for the X300 is not interchangeable with the black one for the V8 X308

To test the relay remove the 3 wire connector on the rear left lower radiator , coolant temp switch and not a sensor like on X308

Jumper with a paper clip one white wire to the black and you will tell the relay to close for one or both fans running modes

remove the paper clip and jumper the other white wire only to the black wire and you will get the other one or both fan running modes

This is a low power control circuit so no high amperage arcing

make sure the relay is not hanging upside down or water can enter the relay ruining it

the relay connector should be facing down

the large fan control relay is under the car forward of the left front tire

 

As I understand it, the temperature gauge like the oil pressure gauge is an "idiot" gauge, designed to read normal provided the underlying temperature falls within a predetermined range, so the fact that your gauge shows N doesnt mean that the actual temperature is always the same. As has been suggested, I would start by making sure you have plenty of coolant, and if you have a big amount to top up, that may be your issue. Normally when the fans run on after stopping, they run in slow speed, which can be very quiet, so you may not have heard them, and they may normally run longer than you think. That said, 5 minutes would usually do the trick, so your times seem way too long. As Parker has said, the fans are triggered by a temperature switch on the side of the radiator, and not the sensors for the gauge and the ECU.

 

Thanks Gents,
To update, the coolant level was fine, and when i drove the car home yesterday the temperature gauge was in the normal position on the left edge of the N, and no signs of overheating despite some heave traffic on a diversion. When I stopped on my drive I expected the fans to run on but they didn't, I lifted the hood to check as expected them to be on. Appeared normal this morning. I guess it is possible that the relay could be sticking on, or the temperature switch in the radiator could be on its way out.
I should check the relay this weekend as suggested, and see if it sometimes stays on after removing the paperclip.
My concern now is that if ether the switch or relay are failing, I could end up with the fans not coming on when needed. I do plan to replace the radiator hoses at some point, although I believe, and it looks like, a difficult job doing the lower one on the XJR, so would replace the fan switch at the same time whilst the coolant was out.

 

OK so now to add another layer on the coolant fan operation

The second way the fans are triggered on other then the coolant temp switch is the A/ C freon pressure switch

Once the 2 wire low ( normal lower operating pressure ) pressure switch sees that you are running the A/ C it will command the fan control relay to run one fan

The other 4 wire Freon pressure switch is a higher Freon operating switch where 1/2 of the switch commands the fan control relay to run both fans

The other 1/2 of the 4 wire switch is a over freon pressure switch which will unload the compressor clutch

There was a Jaguar TSB to modify the cooling fans that may or may not have been done and this would effect when the fans turn on

The mod invollves removing the connector from the 2 wire low pressure switch and installing a jumper wire between the 2 wire connector

If you do not have this I have an extra factory jumper wire that clips into the hanging connector

Sometimes you will find the low pressure switch removed leaving the 4 wire pressure switch but is not necessary as long as the freon line is sealed from leaking with the switch body in place

 

Thanks, I didn't get chance to test the relay over the weekend due to the usual commitments and the option of another car to get to work, but it has been working normally consistently now running around over the weekend and to work yesterday / today. A useful diagram to have - as the ac has not worked for along time with the clutch not engaging which I have put down to low gas pressure and likely leak given the age of the system. I might see about getting it refilled but not sure if I need it fixing and the there is a long list of higher priority jobs on the car!
Anyway back on topic, if I needed to get the fans running in the event of the switch or relay module failing, could bridging the two wire ac switch do the job?
I realise that the best course of action is probably to replace the switch and relay, which I may well do.

 

At the risk of total thread drift, remember the diagnostic mode for your heating and aircon. 30 seconds of button pushing in the cabin will confirm whether you need a refill or whether there are other faults.

 

In the end the TSB mod to put a jumper wire on the 2 wire low pressure switch will keep the one fan operation running at all times

But this requires the Fan Control Relay Module to be working properly

To run the one fan directly you can obtain plenty of power from the left engine bay fuse box positive terminal post with a small alligator clamp but a decent sized wire gauge