4.0L Heater problem

[xjscharlie]

Hello Folks,
I have a lack of heat on my 4.0L 2000 XJ8 and suspect the control valve as there's some fluctuation in temp control but when on HI the output is nowhere near what it used to be. I've checked the coolant level and topped up with the heater on. Is it possible to clean/check the valve in situ? I have a diagram but wondered if anyone may have a marked up print showing the flow thro the valve? Any advice appreciated. Charlie.

[mike020150]

A common problem is failure of the auxiliary electrical heater pump which assists the flow of water through the heater unit. Follow the line of the hoses to find it usually tucked under the transmission tunnel end of the under bonnet area. Disconnect the electrical plug and then connect a 12v feed to check if it's working. Mike.

[BrianG]

Charlie,
There are no valves in the X308 heater system (unlike the XJ40). The auxiliary electric pump is the main culprit as it is needed to circulate the water when the revs are below 2,500 rpm or so, because the engine pump does not have enough output below that (usually the heater works fine when cruising at motorway speed but is rubbish in normal town driving).

The problem with the electric pump is that the motor carbon brushes wear out and the motor just runs erratically or stops completely. Brushes wear out with hours run, not specific vehicle mileage. If you disconnect the plug and try and test it in situ you will probably find it appears open circuit. The motors can be repaired if you are prepared to make new carbon brushes. Brushes are not available from Jaguar, only a complete pump unit at some considerable expense. The motor is magnetically coupled to the pump so that it is leak free. If you can remove the three bolts that hold it to the pump housing the brushes can be changed without draining the cooling system, otherwise you will have to partially drain the system, remove the whole pump unit, and separate the motor to work on it.

My original brushes failed at about 90K the first time, the home made repaired ones lasted until about 140K; it all rather depends on the composition of the replacement brush material. I made my new brushes from ones that were sold as washing machine motor spares. These are too big and need modifying before use, but you can sometimes find smaller brushes on eBay, sold as spares for model car racing etc. that may do the job. You need the type with embedded braided connection wires. To make new brushes you need to take the motor apart, find the rectangular brass guides next to the motor commutator which house the stumps of the old brushes inside. Unsolder the tail leads and unhook the spring clips to remove the old brushes. These will give you a guide as to the size to cut/file the sectional shape of the replacement brush to go in the guides (but which must obviously be made about 2x longer). Fit the new ones, replace the spring clips, solder up the braided tails. Reassembly is then just the reverse of disassembly as they say in the Haynes manuals!

[RichardSEL]

And if you can reach down the brush holder with a cotton bud sprayed with switch cleaner (no, not WD40 that has an oil base) such as Servisol, give the commutators a wipe too. The spaces between commutator segments like to be cleaned out too