www.jec.org.uk

Evening all, first post so apologies if it's in the wrong place. 2004 XKR 4.2. When the engine reaches normal operating temp (half way up gauge) the radiator fans cut in, both slow and fast speed. Have already changed the water pump and fan module to no avail. Any suggestions as to where to look next? Had the engine temperature tested and it is not overheating.

I suspect you still have air in the cooling system after fitting the water pump. I`ve seen a similar happening on my XJR 4.2. I finally blead off by removing one of the inter-cooler hoses at the highest point.

Mike K

Hi Mike

Thanks for the reply - however the water pump was changed as a consequence of the fans constantly running. Since I bought the car in March it has been back into the garage three times, and has had (apart from the water pump fitted the second time it want back) a radiator module, temperature sensor and thermostat. The fan is cutting in at 93 degrees instead of 110 degrees so I'm wondering if it is anything to do with the ECU telling the fans to cut in too early

I don't think you've got any problem! Your system is working in exactly the same way as mine (Not that that proves my point! but it's always been like that)

93 deg C is the correct fan cut-in temperature. Thermostat opens 84/86 deg C and is fully open at 96 deg C. The fans are designed to come on together, initially at slow speed and thereafter at an appropriate variable speed. They do not normally stop having started. The speed is controlled by a PWM signal from the ECU to the fan module.

Added to that, if the climate control is on, the fans will definitely run continuously, by design.

The gauge first reads N when temp gets to about 85 deg C and remains steady until 110 deg C when it will start to rise again. If it does ever get to rise beyond N, that's usually the start of a rapid rise into the red and trouble.

Resurrecting an old thread here, apologies. After the brief heatwave last week and a long journey my cooling fans were both running and staying on for several minutes after stopping. Ok, so assumed it was the heat and fact we had done about 250miles. However they are now coming on after even a short journey of 2-3 miles, which is a new thing. Coolant level seems ok, 'low coolant' came on once but level is fine. As Jaguar, in their wisdom, fitted a gauge that is next to useless I have no way of knowing if the engine is actually getting too hot. I know water pumps on these cars are prone to fail over time and that the thermostat towers are also fragile. My instinct is to change the water pump as this seems a fairly easy DIY job. Any thoughts?

I guess also worth replacing thermostat first, as that’s even easier?

There's a couple of ways ahead that you might like to consider;

First, the actual value of the coolant temperature is, of course, floating around in the CAN system between the various modules that make use of the information and all you need to read that value is some form of diagnostic scanner. The Viecar that I use and can recommend for quick roadside use is one of these that I keep in my XK8. (Many on Ebay)
There are cheaper versions available as Elm 327, but the see-through blue plastic ones are often of questionable quality

To go with it you need an app on your smart phone. For Android phones Torque Pro is excellent. iPhones have their own range of which I have no useful knowledge. As well as the usual reading of fault codes, you can set up an instrument panel like this and then read your actual coolant temperature in real time
The other thing to consider is converting your temperature gauge so it reads correctly throughout its range rather than as I described in my earlier post above. Not a cheap modification, but a very good, high quality one and found here

https://www.thejagwrangler.com/

Thanks for that information

An update, replaced thermostat this morning, old one definitely seemed to be faulty as not opening in boiling water, so hoping that solves the issue. Have also purchased a new code reader as suggested, which connects to the phone, so at least I can get accurate temperature readings. If problem persists then water pump replacement next.