The only really serious problem that Ive had with the cooling system since getting the one owner ZR in 2010 was with the experience of having no heat in the cabin. I had replaced the radiator, which was very badly corroded along the bottom edge, most probably due to a long term weak and incorrect coolant mix, new top and bottom radiator hoses were also fitted at the same time, also adding a correct fill of fresh coolant.

Replacing cabin heater matrix valve on the 2004 ZR


The heater matrix valve as shown, is basiclly a SAAB C900 unit and usually comes supplied with 4 new coolant hoses already attached. 

Using a further trial and elimination process, the cabin heater control dial was set to hot position, radiator bottom hose detached and coolant drained off yet again. For this purpose a clean and cut to shape washing up bowl was used. The first to check were heater control valve located on the bulkhead, the cabin heater control dial, and then the heater matrix. 

Cabin heater controlled coolant valve JJB-100240 attached to the bulkhead, is nothing more than just a simple sliding coolant regulator or shut off valve, operated directly when rotating the cabin's heater dial for either hot or cold air, this had no issues with opening or closing, and was working as it should. the heater control dial was rotated a number of times to confirm the operating control rod was working correctly.


Next to check was a possibility of a blocked heater matrix, with a clean tube attached to the inlet pipe, a light blow through test expelled clean and clear coolant just same doing the outlet pipe, no blockage was evident, heater matrix valve was now being suspected. The heater matrix valve, routes hot coolant which is circulating within the engine, to the cabin heater, an internal fault in the valve would restrict this process.

With a new valve fitted, and all coolant hoses attached, the cooling system could now be filled after first replacing the small loss of coolant from the cabin's heater matrix during my earlier test. With the return hose, smaller of the two detached from the elbow joint, located front of engine, coolant was poured slowly and directly back into the heater matrix. No specific amount just needs to be in there first to avoid an air lock. 


With heater return hose attached, and heater dial still set to the 'hot' position, commenced on a slow filling procedure. A really slow fill is the key to a good result. As free flowing coolant emerges from the coolant rail, the 8mm bleed bolt can then be refitted back, this needed to be done 'without a break' from pouring in the coolant to a maximum plus fill level, replacing coolant cap, then running the engine 'only' on tickover.

Increased engine revs and radiator hose squeezing isnt necessary during this, the added volume of coolant should search out all areas within the system, coolant level when being checked on a 'cold engine' may need a tad to be syphoned out, my preference has been to retain at a constant maximum plus fill level without any problems. A fully working heater all year round, and especially during the winter months is essential.   

Rover 200/MG-ZR Technical and Information Pages (c) 2004-2018.

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