M42 overheating at idle/low rpm, lose heat

[sepehr]

My 318is starts to get hot slowly when idling/stop and go/climbing a hill at low rpm. Cools down quickly if I rev the engine it up above 3000 rpm.

The heater is the opposite: I have heat at higher rpm on the highway, lose heat at the stop light.

I have a new waterpump in, and changed the thermostat a few months ago; both were attempts to fix this problem. No cigar. System has been bled, rebled, then bled a few more times.

Any suggestions?

[craig4ie]

sounds like something's restricting the flow, if there aren't any bubbles in the system then it could be a partially plugged rad

[volgapower]

check the thermostat, it might not be opening at a right temp, or even at all... it might be jammed... ;)

[DanielHStout]

I would have your radiator tested.

[e304me]

did you overheat recently? how high does the temp get? is there a fan and shroud on the engine?

[sepehr]

The fan and shroud are on, the fan clutch works.

I had the rad flushed by a reputable BMW mechanic (Nixon Automotive in Burnaby, BC) about 9 months ago, and I think I remember them saying it was OK. Hopefully there isnt a restriction in the engine coolant passages.

The waterpump DID improve things a tiny bit, as the old one had a somewhat degraded impeller. Then again I might be imagining things.

I'll take another look see at the thermostat.