I am having intermittantly poor heat performance from my 2004 S-Type, 4.2l V8 non-supercharged, without Navigation unit. 65,000 miles.
At times outlined below, it blows cooler than normal.

Fresh Coolant and Heater Core prior to my taking onwership one month ago. It is unlikely that the core is restricted, but I may attempt to backflush anyway.

DCCV seems to be working properly. Heating/cooling responds when temps are adjusted through the control panel. All three coolant pipes are hot. CCM is good as verified through test procedures found on www.JaguarClimateControl.com .

I know that one of the three Air Discharge Temperature Sensors may be bad as the ohm reading was different on one of the three. I have ordered a new one. I'm not clear if one bad sensor (the one behind the glovebox)would produce the issues that I'm having and would appreciate input. I also recently cleaned the sensor above the ignition as it was filthy. When I did that, it seemed to marginally improve the performance of the Climate Control System. The previous owner was a smoker...

Outside temps here have been on the 20°F-30°F range. Car temp gauge indicates that the engine seems to be heating up normally. Needle indicates 12 o'clock position most of the time and only fluctuates to just shy of 12 o'clock or just past. I gather that this guage may not be quite accurate.

When just past the normal mark, temperatures at the panel vents are 130°F at all RPMs on all sides of the car and it appears to properly function.

However, when the gauge indicates just on the cooler side of the normal mark, temps at the panel drop to 110°F. This temp noticeably feels cooler. With this, I started to think that my thermostat was stuck/sticking in the open position.

I hesitate to replace the thermostat because JTIS says that the thermostat starts to open at 190°F-198°F. Every parts store I check tells me that the OE temp rating is 183°F and a 192° thermostat will cause overheating issues this summer. Is this right? If I install a lower rated thermostat, won't it complicate my issue? They act as if I don't know what I am talking about when I say I need one rated at 192°. Can anyone clarify this?

Most of the time, the temp needle is slightly left of the 12 o'clock position.
I don't know what the exact coolant temperature is.

When this is the case:

At any RPM, when the fan speed is set at 100%, panel temps drop to 110°F.

At any engine RPM when the blower speed is reduced to 50% or less, the temp at the panel is 130°F+. The lower the fan speed, the warmer temperature can be attained. This was leading me to believe that the thermostat may not be the problem and I wondered if the Aux. Coolant Pump is intermittantly cutting out. I'm uncertain how to test it without removing it from the vehicle. Advice? The fuse and relay are good. I normally would not be opposed to removing it to test it, but my garage is not heated and it's reallly cold out right now. I'm not seeing anything in JTIS on this subject.

It makes no difference if the temp is set to "89°" or "HI".

I am the type of person that does not like to throw parts at a car and hope it fixes the problem. I like to properly diagnose and repair the problem. I also try to fugure out why the part failed in the first place to avoid future problems. I know it's a little OCD but it's how I am...

I've searched the forums for days and can't seem to find anyone with my exact issue. I know that climate control issues are plentiful, so I am sorry if this seems repetative but I am convinced that my DCCV is functioning.

So, is it likely the Sensor, Pump, or Thermostat? or all of the above?
Any techs aware of a common issue on this year and model other than the DCCV? It's got me stumped. I hate intermittant problems. It would be easier to track down if it were constant.

 

Mmmmm, one if my mob, "why is it so" sits perfectly.

NOT a 4.2 guru by any means, but here goes my thoughts.

The fluctuating engine temp gauge is odd on these unless something is out of whack. The thermostat is that item. They do work rather hard and do wear out regularly. The temp range I will stay out of coz I have no info at hand on it, other than the aftermarket down here are not known for their accuracy.

The pump can be an issue, and usually by placing your hand on it when it is "supposed" to be operational will feel a vibration indicating it is electrically operating, the pumping verification would not be so easy.

I know it is a N/A car, and I know the S/Charged can be a mongrel to air bleed. Maybe it has a small pocket of air in it, which would explain nearly all those symptoms.

The lower the cabin fan associated with hotter air does have me thinking in that way. The change of radiator and heater core at the age and mileage is a tad strange to me?.

 

Look up ETM - Engineering Test Mode - on here and you can then monitor the coolant temp as seen by the car. Or get a $15 OBD tool. At least you'll know more

 

Thanks for the tip. It was very helpful.

This morning it was 23°F/-5°C outdoors.

Drove to work while in ETM:

After sufficiently warming up, the coolant temperatures only ranged from
79.3°C/174.7°F to 83.4°C/182.1°F. Never even came close to the specified 88°C/190°F.

Looks like I will be changing the thermostat. Hopefully that cures the problem. I will check the pump while I'm at it. I'll update when complete.

Thanks again.

 

I installed a new thermostat, replaced the sensor, and flushed the coolant.

As far as I could tell, the Aux. Coolant Pump was working (it was vibrating when I touched it).

Now, I have proper heat when I want it.

I love it when it's a simple solution.

 

Very good.

I am pleased you are warm and fuzzy once more.

Like I said many times before, "These are simple cars with simple problems, that get complicated by the human brain"

Sometimes we ignore the obvious and try and complicate the car too much. Nothing much has changed in the basics since the "T".

 

Which sensor did you replace?
.
.
.

 

ECT I reckon.

 

The Evaporator Temperature Sensor. Motorcraft p/n YH1504
JTIS calls it "Air Discharge Temperature Sensor"