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[Bob G]

that after doing a good flush and refil with GM coolant not have the heater?  I ask because did the above yesterday and while running with water or flushing agent in the heater was bloody hot, today it was the exact opposite.  Top bottom hoses nice hot, top heatr pipe hot, rad top and bottom hot, so is it possible that the cleaning process has released more crap? the colour of the first flushes was quite grotty.

[dbug]

Always posssible, or may be an air lock - did you run up to temperature to bleed with heater set on max heat?

[biggriffin]

as above,
 set heater to max then allow to run up to temp.

[Entwood]

as above ..

but with the expansion tank lid OFF and once "on temperature" squeeze the large water pipes in short sharp movements to "burp" the system and move any airlocks ..

[Elite Pete]

As above but on level ground 

[Bob G]

so we seem to think it is an air lock then, just seems strange it was fine with water 

[Bob G]

convinced no airlock, ran up to operating temp, warmish air comes in then changes to cool, so still think a blockage somewhere

[Selseybill]

Did the heater run nice and hot before ?

[Selseybill]

Try running up to temp until the fan comes on 3 times with the cap on

[Bob G]

Did the heater run nice and hot before ?

Yes it was sorted by James v6CDX on here and was cracking, also while doing all the flushing it was perfect, only since the addition of the coolant has it stopped

[Selseybill]

sounds like a air lock to me. I know people say bleed the system on the level but try jacking the car up one side so the expansion tank is the highest part. This way the air will seek the highest part.

[Bob G]

well done that, no change so thought back to the start, drained all coolant and refilled with everything running, heat setting now rivals air con

[omega3000]

Had a blocked radiator on mine that was causing problems , does the car overheat on a run or in traffic ?

[Abiton]

Have you checked that the vac hose that goes onto the HBV isn't sucking?  If it is, you should see an instant improvement in cabin heat by disconnecting it from the HBV and plugging it.

If that seems to be correct (not sucking when cabin controls are demanding heat), I'd try backflushing the matrix alone, with lots of water pressure and flow, in case the overall flushing has just relocated stuff into the matrix, which has the narrowest coolant pathways in the whole system AFAIK.

[Bob G]

Not overheating runs sweet, my own thoughts were that the full flush has blocked the heater matrix again, need James off hisath bed as he can remove those hoses so easy, and he has a hose pipe