Hello guys,

I have the following problem and it drives me really crazy because I have already changed lots of parts and the problem is still not solved.

The coolant temperature increase in a normal way after cold start.
But when I drive slowly with about 1000-2000 rpm engine speed the coolant temperature raises and exceeds 118 degrees. This happens more often when I wait at the traffic lights.
If I press the accelerator paddle and the engine speed increases to about 3000 rpm or higher the coolant temperature drops down to 90 degrees immediately. Therefore I can drive fast and with high rpm without getting a temperature issue. But when I have to stop at the traffic lights or drive through towns the coolant temperature increases.

What could be the issue?

I have changed already the following parts:
* auxiliary pump (new - from Bosch)
* cooling fan (it was faulty but that did not solve the problem)
* thermostat (new from JLR dealer)

I have read something about a bypass valve in the workshop manual of the XKR (X150) but I have the feeling that I did not fully understand it. Does the XKR have an additional bypass valve in the thermostat housing beside the normal thermostat which could regulate the cooling flow?
I have added a screenshot of the part which I meant and made it yellow

Here is the link to my video which shows the problem. The cooling temperature increases and if someone pushes the accelerator pedal to increase rpm, the cooling temperature drops to a normal level.

 

Is the cooling fan really working?

 

Yes it is. Checked with SDD and also by looking into the engine bay

Fan pwm is 90% in that case. If I stop the engine the fan is still running but slows down because the cooling temperature decreses to normal level

 

Dirty radiator - - - Remove debris from radiator fins
Too much 'Coolant' additive - - - drain some fluid, about one gallon, and add one gallon of distilled water
Water pump failing - - - replace water pump, but you already have.
Fan not operating, but you checked already

Me, I'd suspect Too Much Coolant in the system.

 

Thanks for the tip...there is too much coolant additive in the system but I would not thought that this could affect the cooling performance?

I will check that in the next few days and fill up the correct ratio of water and coolant additive :-)

 

For a back story, about thirty years ago I bought a 1979 Thunderbird (nice car!) off a guy because he could never stop the overheating problem. I paid $750 for an $11k car.
Sure enough, on the sight mile drive home it overheated. I sat for awhile and drove the couple miles farther to my garage then parked it overnight.
Next day I checked the coolant level, which was full, but it smelled a LOT like straight coolant, which it was. I drained out all I could and replaced it with distilled water, took I think three gallons.
I had that car another five years and it never had a heat problem again. It cost me about three bucks for water, but I got $30 back for the three gallons of straight anti-freeze.

'Coolant' sucks as a coolant, as it is merely an anti-corrosion additive with another anti-freeze additive. It doesn't transfer heat for crap. Water does though.

 

And sorry, have to ask. Was your thermostat the one that comes in parts? Was it installed correctly, and not backwards?
Also, ​​​​​​@Cee Jay is spot on. A complete flush might tell wonders?

 

Found that very useful, as I hadn’t thought about it before, and my personal experience was different. I had a ‘68 Grand Prix, and I just ran straight coolant, no water, in it. Figured it gave me better protection for those cold winter nights, as I needed it as my daily driver, and no garage in WI. Ran fine, no over heating.

 

No the thermostat was one part.
Yes installed correctly.

I will check cooling fluid first and if thats not rhe root cause then I will check the thermostat housing incl thermostat :-)

 

Everything from this post is of a general nature...not XKR specific.
Reving the engine to cooler down indicates 1. A restriction in coolant flow...garbage in the cooling system or radiator. assuming the thermostat/water pump is operating correctly.
2. coolant level low. wrong mixture/ air trapped somewhere. also check for Hydro carbons in the coolant. (this would indicate coolant getting into the cylinders). Could be very minor but still relevant.

 

My wife's old Lincoln LS was a pain to get all the air out of. There were either two or three bleed screws that had to be loosened to get all the air out. It was a miserable system and the zoned climate control barely worked anyway.

 

Bleed the system properly. Pressure bleeding will fix it.

 

I have bleeded the system at the expansion tank with the bleeding screw exactly like in the workshop manual. :-)

 

Also, use an infrared thermometer to see where the coolant is or isn't flowing. I think Cee Jay is pointing you in the right direction but an infrared thermometer will tell you what temp the thermostat is opening and closing, whether it's opening and closing. Same with the water pump flow and radiator flow. Cheap to buy, easy to use.

 

Water pump might be going bad. I was told that the water pump on the XK's has been a known issue. You might also check your thermostat.

 

Chibbi, what detail can you share regarding how you linked your phone to the engine readouts you have? Likely a Bluetooth app.
Thanks!

 

WP issues are on the 5.0 engine. OP has a 2008 XK, but yes it should be part of the inspection.

 

air stuck in system

 

The app to use with the obd reader is Torque pro. Works with both Android and Apple operating systems. Here's a link: https://play.google.com/store/apps/d...orque&hl=en_US

 

Okay I have removed some cooling fluid and I have added destilled water (50:50 mixture).

Engine exceeds still 100 degree in idle.

I have checked the input connection of the radiator. It is really hot but the radiator itself is cool.
The output side is also cool.

If I hit the accelerator pedal the temperature decreses immediately and I can feel with my hands that the radiator gets hot. Same for the output side and hose.

I have the feeling that the radiator is clogged. What would you guys say?
Is it possible to clean the radiator with the high-pressure cleaner while the radiator is still built in the car?