I have to drain and refill my coolant system on the XJR soon. The cabin heater matrix has a constriction on the drivers side and heating is disappointing. I`m hoping I can avoid the costs and effort of replacing the matrix (£120 plus VAT) by draining the system of anti-freeze coolant, flushing, adding rad flush, running the car around, back flushing with a hose and finally replacing the coolant.
Here is the plumbing diagram for the XJR 4.2R. The naturally aspirated engine is similar to the R model with the exception of the supercharger coolant section which is obviously not fitted. Here is the diagram of the system which Pop Rivet earlier described as looking like the London Underground plan!
As you can see, the pipery is something of a plumbers nightmare. Space around many areas is tight and breaking into the system at various points is difficult without ripping half the car apart. The radiator drain tap is on the near side lower corner of the radiator. My under-tray is off the car so I`m hoping access to the drain is reasonably easy. My idea is to drain down as much fluid as possible and then using a combination of domestic hose, a small 12v tyre compressor and a modified used header tank cap, to to pressurise the system lightly using compressed air via a Schraeder valve set into the old header tank cap. Rather than explain what I have created in detail, I`ll let the images below show what I`ve built. The valve came from eBay for £1 including delivery!
Silicon sealant was squirted in between the threaded centre unit and the cap top to provide what I hope will be an air tight joint between the two parts before the peripheral sealing rubber gasket was refitted.
More on this little moded caps success or failure when the weather warms up a bit. Being hot and soaked is fine, being cold and drenched in freezing coolant is another!
Mike
