Scenic 1.9 dti, after a recent head removal due to a timing belt failure, the cabin heater system is not working. This apparantly was because the matrix was not fully bled. This was done repeatedly via the bleed screw on the upper matrix hose. This results in the matrix working for a period but will then become 'air locked' again. Also the bleed point on the thermostat housing, when opened after the engine has been running releases a fair amount of hot air and steam before water appears. The level in the header tank drops simultaneously as the air is released.
I have bled the system numerous times..both with the engine running and not running. There is coolant loss....about a litre in 40 miles. There is no water in the oil. The engine temp gauge is always normal...but an engine warning light comes on occasionally. There is no sign of leakage around hoses or at the water pump.
My questions are (!!)
1) what is the correct procedure for bleeding the system
2) would a faulty thermostat fixed in the closed position cause the coolant to superheat and vaporise causing airlocks
3) could this be a head gasket problem...the car runs well.
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Well if the engine is not leaking externally then it must be leaking internally, the water is going somewhere! So yes, could be the HG gone. Get a pressure test done or ask someone to sniff your header tank with 4-gas probe and see if there is HC there.
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Pressure test showed no leakage . After several 'tests' the water loss appears to be the water being pushed back into the header tank and out the pressure releif cap. There is steam (or gas) pressure building up in the head. The mechanic who replaced the head says it is very unlikely that the gasket is at fault, and there is no fuel or combustion residue in the coolant.( He is very experienced. ). A suggestion is that the pump is lazy. As a test I ran the engine with the return from the heater matrix disconnected and the bypass from the thermostat housing clamped closed, also with a continuous water supply to the header tank. At tick over a good flow of water is witnessed, but it could be stemmed by putting my thumb over the end of tube. With the thermostat closed this is the only circulating flow.
Question; what pressure or flow rate should be produced by the pump at idle?
The car has 100,000 miles on the clock.
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hi
not sure about the scenic cooling system layout but on a pug 205 i was owned the procedure i adopted was.
set heater controls to max heat
lift the header tank temporally to a higher position (tied to the underside of bonnet.
fill with water/antifreeze mix).
open air release valves till water runs clear. close valves.
start engine with presure cap removed, run engine to operating temp and till fan starts, top up header tank if required.
recheck air release valves (carefull scalding water/air). refit pressure cap.
let engine run till fan starts again.
shut off engine
replace header tank to original position.
re start engine run till fan starts again.
take for test run.
after cooling down recheck header tank level and refill as ncecessary.
hope this is of help.
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