Hi gang...regarding my 2009 XF premium luxury 4.2......yesterday for the first time I got a "low coolant" warning, followed by "engine overheating" warning. Pulled over, shut it down. Lifted hood and discovered that somehow the upper radiator hose had come completely off. It had both clamps still on hose and hose appeared in tact. It had one of those pinch clamps on end with a screw clamp apparently as a secondary. Put the hose back on and added coolant. But when I started engine, even though I knew the engine to be warm (if not hot) I noticed that there was no circulation in the reservoir and it did not drain down as if entering the engine block. That puzzled me and concerned me but I decided to try to get the car 5 miles back home. Within a 1/2 mile of home the "engine overheating" message came back on but I managed to get it back in the garage and shut it down. The coolant in the expansion tank went down but not much. I am not a pro mechanic but have managed to keep my older boat engines running and done a fair amount of diy stuff to my 2005 s type with a 3.0.
So my logic tells me the t-stat is not fully opening and my instinct is to access it and replace it, but stupid me......looking at the top of this engine with the top engine shield removed is bewildering as to where exactly the t-stat is and how to gain access to it. I would appreciate any feedback on the symptoms I described and as much help as possible on replacing that t-stat. I could not find any youtube videos of this particular repair on this particular engine. Thanks

 

Have you checked for error codes from the ODBII?

A failed engine coolant temperature (ECT) sensor shouldn't cause it overheat immediately, if the ECT fails the ECU reverts to the oil temperature thermostat to manage the engine temperature.

The ECT is on the throttle body.

 

Thanks for response. The drawing does not look like mine. Maybe I'm looking at it wrong. I will double check. Here is pic of top of my engine and throttle body. It appears to me that I have to remove a bunch of stuff on top before I can even get to thermostat? And are there two separate coolant entry pipes? I don't believe both are plastic in my case but again, I'm just getting into this issue.

 

update on this.....this morning I decided to start car and check things out. It starts right up and no odd noises or exhaust emissions. Put OBD reader on it and there are 0 stored faults and no new ones popping up. All active monitors that I have running on my Torque app look normal at idle. I let it idle long enough for engine temp to climb to about 120 degrees F.
However.....I wanted to see what happened if I blasted full heat. Result....there is no heat. At maximum HI whether on defrost or floor vents, air coming out is ice cold.
Not sure if this is having effect on engine cooling or what. Also, I am still perplexed on how and why the upper radiator hose came off altogether in the first place. On that day, I had driven the car about 15 miles to a friends house, no issues. Parked there just a few minutes and drove away, no coolant on his driveway observed or reported. So that hose for some reason came off by itself on the return trip home. At first, I could only guess that extreme back pressure from radiator? blew it off????
With the hose back on and coolant in the system, there are no coolant leaks evident whatsoever.
So, why did the hose come off? Why was I getting both the amber overheating warning and the red overtemp warning, with coolant in the expansion tank. Why is there no warm air coming out of vents with climate adjusted to HI full fan.?

I need a little help.

 

Sounds like you have air in the system, which is to be expected with a hose popping off.

I'm not familiar with the 4.2 V8 so I'm sure someone else can help with the official coolant bleed process, but the general process would be:

• Remove expansion tank cap
• Loosen coolant bleed screw
• Refill until coolant comes out of the bleed screw overflow without bubbles
• Tighten bleed screw
• Replace expansion tank cap
• Start engine and turn heaters to max and run until hot air comes out of face vents

 

I think the ECT is under that collection of hoses. It looks like the two hoses you can see in your picture are the ones on the back of the diagram only the diagram is upside down.

Below is the workshop guide. However given you've blown a hose that doesn't sound like it's the thing. As davetibbs says, likely to have air in the system.

In terms of the climate control there are many things that could be wrong, one being air in the system. The engine coolant pump is driven mechanically by the engine, however the climate control system has its own auxiliary coolant pump and if this fails then little coolant will reach the heater core (the flow diagram is below). There could be a problem with the thermostat, or any number of temperature sensors.

 

The water outlet, which includes the thermostat and coolant temperature sensor, should be replaced when the coolant is replaced as it can withstand a finite number of cold to hot to cold cycles before failing.

The part number for the water outlet is AJ811793.

 

Thank you nbcat. You have helped thru other issues on my s type. Curious if you have a theory on how that upper radiator hose came off in the first place, and how concerned are you that lack of cabin heat indicates a heater core which could be source of overheating? I have had heater core go out on other cars before but in those cases, coolant was leaking into the cabin footwells. I'm really hoping that my problem is either/or the thermostat or air in system since the hose came off.

 

Replace the water outlet and then get air out of the system. It may also be wise to replace the upper radiator hose since it's already disconnected at the water outlet end. Do not use jubilee clips or worm style clamps as the will cause the plastic pipes to eventually fail.

 

Thanks for guidance. Update, I did the plastic water outlet assembly and bolted all back together. Started car after adding coolant and I did get good climate control hot and cold. HOWEVER....it may be that the water outlet pipe assembly was not my primary problem in the first place. The old one appeared undamaged (but I did boil test the t stat and it did not appear to open at all). I have a fast and steady coolant leak that I can not actually see other than the liquid dripping onto the lower reaches of the engine and into a catch pan, and only with the engine running. There is white staining around the water pump on the block although as I said I can not see coolant escaping down the block from behind the pump pulley. I'm assuming it is there though. Are there any other possible sources of steady coolant leaks in that area other than hoses? They all look good and dry. Also, this does not appear to be an impossible diy job, but it does seem like for ease of access, I gotta pull the throttle body and the outlet pipe again. What makes this a $1200 dealer repair? The water pump seems to be pretty inexpensive online and 4 bolts?
Your help is always appreciated. BTW, the oil looks fresh and uncontaminated.

 

I am a newbie in England . My thermostat appears jammed shut . Therefore I took it to the Jaguar dealer and their engineer refused to replace the Thermostat in a 16 year old piece of Plastic . Part no AJ811793 is on back order from Jaguar UK and has been for three months. You will be fortunate as there are still one or two in the USA. My XK is therefore unuseable until further notice . This also affect XF ,S type & XJR. I suggest you find this part & purchase it pronto

 

Look at on google , search shows options, Stating in stock....

 

In Stock in the USA only , Not in Europe or the UK

 

Oh, if you are in Europe or UK. You can get from U.S. in less than three months... More shipping costs, but you'd be done with it... I've ordered from UK when it was backordered in U.S.

 

Jaguar purport to have parts for10 years relating to all vehicles which have ceased production. They refuse to hand over the drawings in order for this part to be patterned and they also refuse to remanufacture the part. It's called a rock & a hard place