I have a 99 jaguar XJR 4.0 supercharged.

It just started overheating on me the other day. I have full coolant. no visible leaks. The car dose not use any coolant. There is no coolant in the oil. As soon as I turn on the heater full blast the temp goes right back to normal. It will only try and overheat if I drive the car.

I notice that only one 1 radiator fan is working under normal conditions. The one fan that is working is running super slow. I have read online there is a radiator fan control box somewhere. I have not been able to locate this box. Dose anyone have a location or a wright up on how to upgrade to an aftermarket fan or fix the stock one? Also should both fans be running under normal conditions if the a/c is not on?

 

First thought: thermostat.
https://www.jaguarforums.com/forum/x...sensor-172094/

 

Both fans should run. The control unit selects series connection for low speed and parallel for high. I don't recall the location, but if you have downloaded the JTIS21 manual it's in there, or go to jagrepair.com and look for the XK8 electrical guide.

 

Just realized you have have XJR, and I'm not sure the electrical guide will be found in jagrepair. com. But it may be in the DIY or other Sticky on the forum page. I'm sure someone will be along shortly with better directions.

 

I think it's on jagrepair

 

Yes, here is the link. p24 shows the module is at the left front, down low, I think.

http://jagrepair.com/images/AutoRepa.../jagxj1999.pdf

 

If one fan is spinning slowly the motor on it is probably going bad. You can test it by turning on the AC and watching the fans - when the AC compressor is engaged both fans should be spinning quickly. I don't think you can get the motor assembly on its own new, but if you find one at the junkyard it will just bolt up. I believe even some x300's used the same fan assy.

edit: there could also be wiring issues somewhere causing high resistance to the fan. If you have a 12v source you can remove the fan assembly and just stick 12v into each fan and see how they spin to verify it's not the motor itself, then go onto testing wiring

 

I just went out and tested both fans. I started the car turned the a/c on and both fans come on then go off at the same time. Both fans are spinning slowly I can almost spin it by hand faster. Im wondering if its the control module or the fans them self.

I looked at the link that was posted I am having a hard time find the the control module. Can someone post a picture of one and a better location please.

 

p42 section 04.3 shows the RH and LH radiator cooling fan circuit. References the radiator fan control relay module as going to them and the ECM. The fan module looks like a really tall relay.

https://www.google.com/search?q=x308...w=1600&bih=787

You may need to pull the front bumper to access the relay module, I think I remember seeing it when I had mine off. The wires look like they disappear somewhere near the coolant overflow tank, if you pull the front bumper and trace the wires coming from the fans it should be visible.

EDIT: https://www.jaguarforums.com/forum/xj-xj8-xjr-x308-27/overheating-fan-control-relay-41622/

 

I have screwed around with the fan control relay. That dose not seem to be the problem. both fans seem to be working fine. It dose not overheat at idle only; when I am driving the car. Has anyone else experienced any issues with overheating.

 

Are you sure the other fan is turning properly? I say that because what may seem like a properly turning fan, can be a weak motor turning just enough to seem like its fine. If it isn't pushing/pulling air like the other, its gone south.
Turning on the heater is somewhat of a clue....
...when was the last time you flushed your radiator? I don't care what make of car it is, if the radiator isn't clean, it will scale, build up and overheat because fluid can't flow. Be sure to check the water pump also, feel the hoses for strong flow. If its original, it may have lost one of the plastic impellors. Its easy and cheap enough to get a new one with the upgraded metal impellors. I'd do the thermostat while your there, it may not be opening all the way ...what's roughly another $10 to be sure not to have to drain the fluid again. Personally I despise messing with radiator fluid, ...nasty sticky stuff gets all over everything.

 

my coolant was recently flushed it is a very health green color. I was told the t-stat and the water pump have been replaced within the last 5k miles on it.I may swap out the t stat just because its cheap and see if that makes any difference.

both fans seem to be working at like medium speed. anyone have a like a video clip of how fast they should be going? I ordered another fan control relay we will see if that makes any difference.

Is there a special way to bleed the system by chance?

I wonder if it is possible to remove these gay 2 small fans and go to 1 big electric fan somehow. Has anyone done a wright up on this? I will be searching the form seems like someone would have done this before.

 

For fan replacement, its all about flow. You need to find out the flow rate of the pair vs a single. A pair will usually pull more, but new, better designs are always coming out. But also, you don't want to have too cool or warm of a motor. The fans are designed to keep your vehicle in temperature tolerance for what it was designed to operate for. For example, ...too much air and it won't heat in the winter....too warm and you'll be overheat something. There are more issues that are involved, just giving a quick reference.

 

I don't see why you should do that.
If your coolent system itself is allright, then the fans and its operation are more than capable to control the temperature and maintain the range.
We have long, hot and humid summers here, and a lot of mountains, and the only time I had problems was when my thermostat died.

 

You referred that the car overheats when driving it?
Does it overheat at highway speeds, or stop and go traffic?

This sounds like a thermostat or blockage problem to me.
While the fans may be bad also, I would replace the thermo first. It's a simple change and could solve your problem quickly.

There should be sufficient coolant flow and air flow through the radiator at highway speeds that the fans shouldn't matter.

The fan motors are probably bad. If it was the relay, they wouldn't turn at all.
Check the connections of the fan with a voltage meter and see if the relay is triggering the fans. If it is, then the fans are bad.
You can get replacement fans in lots of places. I see them on eBay all the time.

One word of caution :
Don't let this problem linger or else you will be doing a head gasket replacement too and maybe more.

 

well it can be at idle all day and not overheat.

as soon as i drive the car 3k rpm and above it starts to overheat until I turn the heater on then it goes back to normal. I will be re replacing the t stat today.

I agree when driving I should have lot of airflow and cooling should not be a problem but it seems to be. I have stopped driving the car until I can figure out what is going on.

 

if i replace the thermostat do i have to replace the coolant?

 

Jaguar XJR Problems | CarComplaints.com

"The 1999 Jaguar XJR has the most overall complaints, & the most-reported problem is also with the 1999 XJR for overheated."

 

No. only if it needs it.
You WILL have to top it off though as you will lose some in the dis-assembly process.

 

There's only one complaint logged there among all the xjr years, where someone's engine overheated at 135k. notes are replacing theromstat and head gasket, so probably a stuck thermostat caused it to overheat. Wonder if that was the original thermostat that gave out too...

Who told you that the thermostat and water pump was replaced recently? Previous owner? Did they give receipts or any documentation?
Even if they did replace it, it's cheap and fairly easy to get to, on the off chance that the thermostat in there is bad. You can drop the old one in some boiling water and see if it opens up.