On my 02 XJR i had a leaking coolant hose replaced recently. It was the pain in the *** one under the manifold.
After picking up the car & driving home I did notice that when I turned off the ignition the engine cooling fan was running for about 2 minutes after the engine was turned off. Unusual as it seldom did that in the past (I've owned the car for 8 years).
The next day I checked the coolant level & it was full. Drove the car as I normally do for a week & every time I drove it (up to normal operating temperature) the engine cooling fan would after run for 2 minutes, This was abnormal for this car but I kinda shrugged my shoulders at it.
Yesterday after having driven for about 30 minutes around town & whilst at a stoplight I noticed the temp gauge in the RED !! Holy crap! When the light turned green I immediately pulled over into a parking lot & shut the car off. Opened the hood & noticed that both the engine cooling fan & the auxiliary cooling fans were on. Oh boy thought! it must have lost all it's coolant.
The fans shut off after a few minutes. I left the car for awhile to allow it to cooldown for a bit. After 30 minutes I carefully opened the coolant cap, fearing the worst (empty reservoir) I lifted the cap & found the coolant tank full of coolant !!
I went in the car & turned on the engine & saw a :Low Coolant" warning light & the temp gauge at about 5/8
Low coolant light went off after about 15 seconds.
I left the car in a safe place for now, probably going to tow it to the shop but they are booked for 2 weeks,
Anyway hopefully folks here can share their thoughts on why the temp gauge would have gone into the RED & both cooling fans ON with a full coolant tank + a low coolant light on.

TIA for any tips or constructive suggestions

 

Are the lines on the front of your coolant overflow crossed or straight? They're supposed to be crossed. Whenever these are disconnected, non Jag techs usually reconnect them the wrong way because the right way just doesn't look right.

 

potential head gasket or water pump issue.

 

This is something I will check this afternoon. thank you

 

If the coolant levels were full after a 30 minute drive and no issue before the hose was replaced,
it is doubtful there are mechanical problems causing this. They may indeed have crossed the
lines as they probably wanted to empty the overflow to prevent antifreeze loss during the coolant
evacuation phase of the task.

 

Back in the late 1990s when Jaguar launched the XJ8, we had a X308 come in for cooling system problems. (lots of trouble with water pumps and thermostats)
The shop foreman was the one working on the car and finished right around 5 PM quitting time.

He left and the car left with the owner.
The car came back spewing coolant out of the atmospheric catchment tank. The customer was NOT HAPPY.

I was still working after 5 so I pulled the car into my work bay and looked at the leak.
It did not take long to see that he had 'swapped' the air bleed line with the catchment tank line.
I swapped the line back and refilled with coolant. Sent the customer on his way.

Shop foreman took a 'ribbing' the next morning for his mistake!!!!!!!!!!!!!!

 

I check the hose routing & they appear to be the same as the sample picture provided

 

Nuts, was hoping for a nice straightforward solution.

 

I think there’s 3 things you can do that’s not terribly difficult.

1) Get a 17mm Allen socket or get a 17mm bolt head with 2 nuts tightened down against each other and put it in the supercharger coolant cap next to the passenger side intercooler to open it up with a wrench and see if there’s any air in that system. You could possibly use some large channelocks or vise grips. It really depends on how tight that nut is. *Warning*, I’ve seen those cap seals come apart when you take the nut off so just be aware.

2) Replace the thermostat and gasket. It’s a little messy but, it’s easy enough to do since it’s at the top of the engine.

3) When the engine is warmed up, run the heater full blast (A/C button off) to make sure all the air is purged from the cooling system.

 

Make sure your thermostat isn't sticking, or installed backwards (I did this once, whoops). Is the radiator return line (the one going into the thermostat) warm to the touch, checking close to the rad, when the temp gauge is at operating temp? If it's cool to the touch then your tstat isn't opening up.

If you're really concerned about it you can try taking the tstat out completely and run like that a little bit. It might leak... but it'll allow for flow.

 

Thank you very much to all that responded. As it appeared to be the most economical thing to try (to me) I changed the thermostat & drove the car 20 miles with no issues. Drove the car today 70 miles & I am happy to say no more running hot, the cooling fans no longer run when the engine is turned off.