What's the best way to flush the coolant in the 300TDi on a defender? Also what is the best way to make sure there are no air locks?

I had been having issues with the gauge reading hot when the engine wasn't and this was following removing the matrix and re-fitting. Over the space of 100 miles and a few days it settled back down and is right again but I'm still having problems with look-warm air from the heater even with a new matrix, heater box rebuild (insulated, foam replaced and all holes sealed with aluminium duct tape), no leaks in system, fan working and cables adjusted - It blows hard through the vents but just has no heat. I've got a new sender, thermostat and gasket ready to fit but thought I would give it a clean out whilst I'm at it. The coolant is at 50/50 and is only 3 months old but It's cheap enough so thought I would do it again after a wash out.

Thermostat may not be opening fully would try changing that first.

danny6801 said:

Thermostat may not be opening fully would try changing that first.

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I am changing the thermostat but I was just asking the best way to flush it

Put coolant flush in let it run threw then drop coolant at bottom of radiator. then run a hose threw it till it runs clear then refill with correct amount of coolant leave expansion bottle top of with heating on full till you get rid of all air job done.

Does anyone have any idea why people keep saying "have the heating on full". Doesn't the coolant run through the matrix all the time and it's just down to the hot/cold flap where the air goes??

Any suggestions as to the best coolant flush?

Not sure but also tells you that thermostat is open fully and running threw the heating system with no air leaks.

danny6801 said:

Not sure but also tells you that thermostat is open fully and running threw the heating system with no air leaks.

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I think it's just something that people have always been told and keep passing on. Having the heater on or off wouldn't appear to make a blind bit of difference to the actual flow of water around the system at all....

Just need to pick up a 20 litre can of coolant and some flush and I'll sort it in the next couple of days

cowasaki said:

Does anyone have any idea why people keep saying "have the heating on full". Doesn't the coolant run through the matrix all the time and it's just down to the hot/cold flap where the air goes??

Any suggestions as to the best coolant flush?

Click to expand...

Because. They are old school and don't know about an air blending heater system.
But then a 3.9 disco with air blending and fitted with ac has a coolent cut off valve.