Help??

2006 XJ8 x350 base model. 130K miles we've had it for about 3000 miles but the previous owner had not taken care of it so we've done a lot of work on it not listed here.

We have been tracking overheating issues for several months now:
Before we purchased the car someone had replaced the radiator due to very minor front end damage.
We have done the following:
re-drilled and replaced ALL the grounds (studs were corroded)
replaced the broken thermostat and internally cracked housing (found every little piece, we were lucky)
replaced the aux water pump (it was dead)
replaced a cracked reservoir (cracked at the little pipe by the bleed valve)
emptied the system and replaced 100% new coolant (proper orange stuff, that was what was in it. No evidence of clogging or jello).
replaced a faulty coolant temperature sensor today (it just decided to die and read zero. It had been acting weird for a few weeks and throwing cold start codes as well)
bled the air out of the system multiple times, with each repair, and again today.
(it took a while to get used to this burping system but we've got it down now, yes ran the aux pump and got heat going)
We checked the fan today by disconnecting and jumpering the green wire on the small connector. It runs full speed.
We reset the ECM again today. We were hoping it would re-learn after having a decent temp sensor.
I was afraid it might have confused the computer.

We have a high end ODB2 code reader. So we were watching real time ECM data.

Now we still have the following issue:

95 degree day, 75% humidity, air-conditioner full speed and running hard.
When driving at any speed above about 20mph the temperature runs about 208-228 depending on speed.
At 70-90 mph it runs rock stead about 210. Air input temperature is 90. If you push it to 110 it comes down to about 200 even.
The car seems to be happiest and runs the smoothest at about 105. I think it could run there all day.
At idle the temp will slowly and steadily climb to about 246 after about 5 minutes of idling.
At 248 the red light will come on around 7m. If you then shut down the engine of course the electronic fans are running constantly for about another 10 minutes.
If you however start driving again and get the car over 30mph it comes down almost immediately to below 220. By immediately I mean after about 100 yards of driving or less.
It comes down very rapidly.
After we bring it home again we let it idle for about 5 minutes. Checked the bleed valve on top of the reservoir and there is no air coming out just a nice steady stream of coolant, no bubbles.
Of course the temp goes up to 250 just like before and the fan is running full tilt so we tightened up the bleed valve and shut it down.

Ok now here's the interesting part...
If you let the car get to 248 and the red temp light comes on at idle after 5-7 minutes, then if you rev the engine (in park) to about 3500RPM, after about 10-15 seconds the temperature will almost immediately drop to 225ish. If you do this every 2-3 minutes it will never get to 240.
During this time if you step out of the car the fan is obviously running at full speed. When the temp comes back down to 225 it slows down to a normal speed again. I'm not exactly sure when the fan picks up to full speed but at full speed and engine idle about 800RPM it cannot keep up. It raises the temp very very slowly up to 246 and you think it's going to hold there because it stays there for nearly 2 minutes but then finally it hits 248 and the light comes on.

I can't imagine trying to drive this car in stop and go California traffic...

My theory is that either the flow through the radiator is restricted a little or the water pump can't quite keep up with the flow rate needed. When you increase engine RPM at idle the temp comes down dramatically in just a few seconds.

I'm thinking replace the water pump next. Ideas?

Steve

 

You have not mentioned a coolant water pump fail eg plastic vane fail

and possible blockage in the system.The plastic 'tree' is known to fail

internally but hopefully you would have found that when replacing the thermostat.

 

I was still editing when you replied...
I have no evidence of the plastic tree failing at this point. I did check when replacing the thermostat as I was looking for broken pieces.
Though I do have a new one just in case.
When replacing the thermostat of course that housing had failed and there were broken pieces.
I collected all of them to make sure I wasn't missing any chunks. Got them all (lucky).
I am at this point thinking that the waterpump its self is bad (perhaps broken or damaged vanes)
because when I rev the engine I get enough water flow and it cools right down. I'm thinking that at idle
at 800rpm or so it just isn't enough to move sufficient water.
Steve

 

First thought is the thermostat housing & tstat, which you stated was replaced with new as the old was broken. Barring that, yeah, I'd say the water pump is suspect. In normal service in NC summer I've never seen the temp past 208F in the hottest traffic. On the highway it will settle in around 197-200F.

On a side note, the aux coolant pump only helps the heater, in fact some people in warm climates pull the fuse to disable in summer driving as it only adds to the engine heat load.

 

Agree with mhamilton;
You mentioned the fan running after shutting the motor down.
The following list is what i have replaced, all but the radiators
Thermostat with housing, water pump.
Along with, belt, tensioner, idler pulley bearing, & any suspect hoses.
If it still over heats, an aluminum radiator should cool things down.
Good luck to you

 

My guess would be the coolant water pump, maybe the impeller is broken internally and is clogging the flow a bit or maybe not rotating well enough to flow - possibly seizing.

I'd make sure water/coolant flows freely through all pipes, thermostat and housing and the radiator.

Thanks,

Chris

 

Definitely the water pump needs to be your next investigation. I believe early ones had a plastic impeller, and the blades broke off and clogged the passageways.

 

THANKS guys for the recommendations. I bought a new water pump. The old one lasted 130K miles. I Guess it had a good life.

So I took everything apart again. I figured that since I had it apart anyway I'd replace the entire plastic "spaghetti monster". I had one on hand. I was glad I did as when I was trying to take it apart it shattered. It was definitely not going to last much longer. When I pulled the "new" thermostat housing off a piece of the old octopus broke off as well. Anyway, so new squid monster. I also figured out that this plastic mess comes apart in 1/2 making it much easier to get to the bottom bolts on the air-intake.
So with new plastic over-complex water routing sytem and new water pump, I hooked everything back together, put in new coolant and bled the system. I suppose it was about a 3-4 hour job.
I know I'm slow but it was over 95deg humid and I was out in the sun.

Good news? Now going down the road, unless you go 100mph it stays around 194. Over 100Mph it hangs around 200. At idle even after 10 minutes it settles down to around 196-199.
I looked at the old water pump and didn't see any obvious problems. But at 130K miles I wasn't going to take it all apart and not replace the water pump too. I'm pretty sure now there were internal cracks in the plastic spaghetti monster.
Anyway, Problem solved... at least it seems that way now...

Side note? After resetting the ECU it appears my windshield wipers decided to work correctly again... who knows what lurks in the mind of a Jaguar.

 

Yes all that plastic crap needs replaced it amazes me how they use plastic instead of metal.
The weight, and money saved is nothing really.
Cheap beyond belief if you ask me, for such a luxury car.

 

Just a reminder that 248-250 F is the "fail safe" temperature the ecu uses to shut down the engine. With the new pump it looks like the issue is resolved.

 

The water outlet, which includes the thermostat should be replaced each time the coolant is replaced as they're prone to failure.

 

Very pleased you have managed to sort the problem out. This use of plastic all over the place on parts that are always hot when running is disgraceful when metal parts would not be all that much more, bearing in mind this is an expensive up-market car. Trouble is all the car makers are using it !!

 

Once had a vectra in that drove fine, but overheated when idling, that turned out to be the water pump, the plastic vanes had worn away to little stumps, and the water was just not circulating fast enough at idle to be cooled properly.

 

Used ones with the metal vanes on my cars, & i would use a metal thermostat housing if they were made

 

Glad to hear you got this sorted Steve. I did the water pump at the same time as changing the plastic thermostat housing as mine seemed like the original and was cracked and losing coolant all down the front of the engine. The water pump that I replaced appeared to be the original and as Fraser rightly mentioned, it had a plastic impeller as my car is an early model 2003.