coolant/heater oddity. (318is M42)

[Alistair]

hi there,
So the heater only blows hot air at revs, at idle it goes cold.
heater switch/valve checked and working fine (although electrics disconnected for test)
New radiator. Engine and heater matrix flushed.
The head and thermostat housing get very hot to touch,
temp gauge sits on about 1/4 to 1/3 (though I don't trust it, it flickers and sometimes doesn't work, have done the gauges out and resolder and its been ok)

next in my mind would be removing the thermostat to check and pulling out the water pump.
is there anything else I should think about before I do that?

cheers
Al

[Brianmoooore]

Are the heater hoses definitely on the right way around at the bulkhead?
Loose rotor on the water pump is a possibility.
Other than that, it could simply be a small amount of air trapped in the heater hose, so pull the top one off at the bulkhead, and push it back on again with coolant flowing from the hose and the stub.
Flickering temp. gauge is usually a loose securing nut for the gauge on the back of the cluster, but this is unlikely if you've had it all apart.

[Alistair]

I'm pretty sure the heater pipes are on correctly, it difficult to see -
its back of the head to bottom pipe (feed/electric valve) and top pipe to plastic manifold (return) right?

while filling the system i waited to see coolant spilling from the heater pipes (one at a time) before connecting them
in a hope of reducing air issues

thanks Brian I'll check.

[Brianmoooore]

I'm pretty sure the heater pipes are on correctly, it difficult to see -
its back of the head to bottom pipe (feed/electric valve) and top pipe to plastic manifold (return) right?

That's correct. Coolant flows from the bottom of the matrix to the top.