I recently up graded to a 2004 XJ8 with 100k miles that came from Arizona. Love the car, the ride and the luxury. My first problem with this car has arrived, temp gauge was spiking a couple of times but would return to normal quickly and I lost a bit of fluid on the garage floor. I replaced the thermostat and heat sensor and fixed the gauge problem but I only have heat now on the passages side only. I think I still have a small leak in a hose somewhere because I need to replace small amounts of fluid now and again depending on how far I travel. Looking forward to hearing from this forum for tips and advice, I enjoy fixing what I can. Jag Lovers was a great forum for me with my other Jag's but can't help me with a newer model. Winter is just around the corner so I'd like to get this problem solved quickly.

 

The coolant header tank has a small pipe running into it at the top, and the connection it is fixed to is liable to gradually crack (and eventually fall off), and this lets small amounts of coolant leak out.

The heater problem is well known and is usually caused by a blockage in the heater matrix. Flushing can sometimes clear it, but often a new matrix is needed. This can be replaced without too much dismantling, but is still fairly heavy on labour hours. The matrix itself is not too expensive

 

I think I read somewhere that if your auxiliary coolant pump fails it could cause heating issues. I don't recall if that's only on the XJR or not.

 

Ah yes, the Auxiliary Coolant Pump ! However, heat is coming through, just not on both sides which is the syndrome seen before with a blocked heater matrix.

However its worth checking this component out.

 

Blocked heater core for sure.
The heater core can be exchanged by going through the glove compartment and removing the blower unit which will give access to the heater core.
There are many threads on here and I documented a strip down and replace of the heater core in my X350.
It is not for the faint hearted unless you are mechanically DIY minded.

 

Failed aux pump will cause heat one side. It runs whenever the ac is on, heat and cool. There is a 20A fuse in the trunk that powers it. Typical life is 100k, whereupon the brushes wear out and the motor stops and water flow reduces, and what hot water gets there is cooled before it heats the driver. I'd be checking the pump as is easier to get to and as it is a moving part, more likely to wear and stop.

 

Bite the bullet, its the heater core, saying its the aux pump is wish full thinking , you might get lucky but I doubt it ,most driver side no heat have been rectified by replacing the heater core, as Fraser M said if you like the challenge go for it, otherwise take it to XJ Auto in YYC.


Stu

 

I can't see how an Aux pump failure will only cause the driver side to get no heat and the passenger side to get the heat.

I have done the heater core exchange and opened the heater core and it is a one entry , one exit system. The water flows in one way and out the other, filling the core. There is no way that the Aux pump not working can make the water flow through half of the heater core (effectively heating only 1 side).

Because of the fixed position of the heater core, the only way the coolant will flow through half the core is if the sludge is sat at the far left bottom of the heater core and starts to fill up over time which they inevitably do. There are threads of the heater core internals on here somewhere showing the Gloop buildup. When I swapped mine out there was only a .75 of a millilitre liquid difference between a non glooped core and a glooped one. This was enough to stop the driver side from getting any heat at all.

 

Maybe it is the core, if there is sludge. Careful evaluation of the behavior will help. Low drivers heat at idle and low engine rpm can improve if rpm is 2500. I presume due to increased water flow. Maybe good flow to a partially sludged core makes adequate heat but not great heat. Changing the core seemed harder, and it does wear out, so we may eventually need to do both.

 

And after fitting a new core, i try to run hot air through it every now and again ( even in 100f temps) to just keep the water flowing through it and hopefully stop any gloop collating in that bottom corner.

After a year and testing it yesturday, I still get good heat out of the drivers side vents.