Hi, a couple of months ago I purchased my new to me 2005 XKR coupe. When I was driving the car home after purchasing it unfortunately on a couple of occasions - the first very worryingly and after a few hours of spirited driving on the motorway enjoying the supercharger whine, the coolant gauge suddenly and immediately went from the middle of the gauge straight into the red without any warning. The first time this happened I quickly pulled into the hard shoulder of the motorway and switched the car off to prevent any possible damage from overheating. Without any visible or audible display of an overheat I gave the car a few minutes to cool off and restarted the engine where the coolant gauge happily returned to the middle and did so for another couple of hours before I pulled of at a hotel for the night. The next morning I headed off and again after a few hours driving it happened again, this time I popped the car into neutral, switched it off and coasted for a few hundred meters before turning it back on again. This off and on again seemed to solve the phantom overheat and since returning home it hasn't happened again.

I'm about to do a full service and replace all the fluids on the car so wonder if I should do any preventative fixes to the coolant system in case an intermittent fault is causing this somewhat worrying event? I had thought to replace the water pump, coolant temperature sensor and thermostat as I'm already going to be doing the drive belt and supercharger belt along with any bearings on the idlers if they feel rough at all. The car only has around 72k miles on it.

Thanks!

 

The coolant gauge in these cars doesn't display the actual engine temperature. It's an idiot gauge. It only goes to red when the car is overheating. Do not druve the car.

Replace thermostat, water pump, and any leaking hoses. Also install RealGauge from The Jag Wrangler's website so that you can have a gauge that gives you real-time coolant temperature.


Also, since you have overheated twice and this is an alloy engine, have the car inspected for head gasket leaks.

 

Thanks for the reply. I have had my eye on the RealGauge upgrade since I started researching into the X100 platform but as my car has the factory satnav I will have to retrofit the gauges and replace all the dash trim panels. Not something I don't want to do, just something I'm not quite ready to invest in yet.

The coolant system at the moment is leak free so I don't want to touch too much as is often the case the minute you move some of these older hoses and connections you end up creating one. I have looked and I can purchase an upgraded water pump from SNG Barratt with an aluminium impellor which I am going to go for as I fitted the same type to my X-Type when I did a rebuild of the coolant system on that car and I liked the quality of it. Less likely to fail like the plastic type and it won't corrode like the steel impellors fitted to the cheap pumps.

 

You don't have to retrofit the 3-gauges and remove the satnav to use the realgauge. There is a version that is just for the coolant gauge. That's what I have. I still have the useless satnav in my car.

There is a risk of cavitation with the metal impellor pump. The plastic ones don't fail nearly as much as you would think. The thermostat is most likely what's causing your issue.

 

I will add you can get proper temperature readout from the ECU as well if you plug an OBD2 adapter in and use a phone app. I don't do it routinely because I did get a CAN communication error one time and had to stop/start again, but if i was worried about an overheat and trying to baby the thing home, I can live with the odd CANBUS error.

 

I use an Ultragauge in my cars. It displays a wide range of parameters including engine temp and fuel trims.

 

It sounds to me as if the problem is being caused by a failing temperature sender as there would be other symptoms arising from a genuine overheat. I would definitely change the sender.

Richard

 

I will certainly consider the upgrade for just the coolant gauge then, I didn't actually realise that you could just do that by itself. Like you mention though the satnav is now very outdated and practically unusable so I still would like to retrofit the 3-gauges at some point as they give a more classic look to the interior that I like.

Regarding the impellor material, cavitation is indeed something to consider when switching to metal instead of plastic but the cost of a genuine Jaguar pump is significantly more than the aluminium alternative from SNG Barratt and with the mileage I do a year (~2000) I don't think I'll have to worry too much. Like you say though the thermostat I will definitely replace for an OEM Waxstat unit as it could be possibly intermittently sticking.

 

Good advice, I didn't think about that when it happened and never had my OBD2 reader with me on the journey. If I am out in the car again before the service I will bring it with me so that I can quickly check should it happen again.

 

Good advice, I didn't think about that when it happened and never had my OBD2 reader with me on the journey. If I am out in the car again before the service I will bring it with me so that I can quickly check should it happen again.

 

That was my thought also, after the first occasion it happened when I pulled into the hotel I did pop the bonnet and check for any signs of an overheat. The next morning after the engine cooled I also checked the coolant level which showed to be almost spot on.

 

As an alternative, you can get a genuine Motorcraft water pump for an '02 Lincoln LS 3.9 for about half the price of the Jaguar one. Same basic engine.

 

I used to get this problem, it was the thermostat that was causing it because it was stuck open so the engine never warmed up. It would cause a problem with a sensor or something and the car would say it's overheating when the coolant temp was at about 70C or something. Now that I changed the thermostat the engine warms up and sits in the middle after about 5 minutes of driving. I never get the high temp warming anymore.

 

Unfortunately in the UK I don't think I'll be able to do that, don't think we've got the same access to Motorcraft parts like you guys do across the pond, thanks for the advice though I can take a quick look.

 

That settles it for me then, I'll be doing the thermostat and coolant temperature sensor. I might see about removing the whole thermostat housing assembly and blast it with glass media while I have a good opportunity to do it, also replace all the associated O rings and hoses that connect to it if I can source them.

It seems a lot of the hoses on the 4.2 are very specific and only orderable from Jaguar, many even being special order meaning there could be a big wait time. Is there another source for them or is this the only option?

 

A cheap and easy way to monitor temperature is to use one of these -
P10 HUD Digital Head Up LCD Display Speedometer OBD 2 Scanner Upgrade
Search on your favourite online store using that description. I have it and it works well.

 

I had a very brief sudden overheat issue with my 97 xk8 4.0l last summer. Like others have mentioned, the gauge is not true temp, and only hits max when reaching a certain temp. My issue was a cooling fan, the passenger side(left hand drive)it was blowing the 30 amp fuse. I put a 40 amp in it to get me home. I took out the fans, and the pass side barely spun. I removed it from the shroud and completely disassembled it, cleaned it up, sanded the shaft, lubed the bearings, cleaned off the motor brushes, cleaned up the commutator with sand paper in a drill press, removed all debris and reassembled. Put it back in and put a 30 amp fuse back in, never happened again. Worth checking it was a free fix just took a little time

 

I also just finished installing the real gauge system with the oil pressure option. Took a little time as well but man what a difference, the temp and oil pressure gauges actually show me real readings in live time. Well worth the effort.

also i forgot to mention, I replaced my t-stat housing with an aluminum one, and did my water pump when i did my timing chains. Beware of the four bolts of the t-stat housing they are a pain, if intake plenum is not removed. The two in front are no problem, but the two in the back required me to modify a ratcheting box wrench to fit, and luckily for me someone had already shortened the length of those two bolts, otherwise they would have not come out or go back in with the intake still mounted.