740 Heater Matrix

Air or vapour in the cooling circuit, probably caused by low coolant level or headgasket failure, undo the coolant filler cap after a running the engine for a little while (be carefull, there might be pressure in there) smell inside the reservoir, If it smells exhausty, or petrolly, then the headgasket has breached, otherwise check the inside of the oil filler cap, the presence of quantities of white gunk indicate possible head gasket breach, otherwise you have a normal coolant leak somewhere, the rad cap isn't sealing properly, or it just hasn't been topped up or checked for ages.

Top up the coolant now!!! If the coolant is low enough for vapour/air to be being pumped through the heater matrix, then the level is critically low, and you are risking overheating your engine.

Ken Phillips

Ken I have run all the checks you said and they are all O.K. The radiator is at max so I am not losing any water. The only other thing I can think is thee is some for of partial block in the matrix restricting the flow. I now notice that the gurgling is only if I reve the engine up.