E30 Zone

Hi,
I started to strip down the cooling system on my 318is
i flushed trough the rad (backwards as well as forwards) and the water was a transparent grey film but is now clear. I took a look in the water pipes and there is a grey film...... Any idea what could be causing this and should I flush the hoses and block etc? Have read wiki just wondered if there was anything else I could do......
Water pump and thermostat are being changed as have no history of any change....

Thanks

Could be residue from radweld if there is any previous leak history
I wold flush it using Holts/Comma Radflush to be sure

dont forget to flush out the heater matrix whilst your at it.

Would the matrix need to come out or is it just a case of pouring water in one stub pipe and it coming out the other?

ONLY flush the matrix from the bottom stub pipe to the top.

Ok, I shall use these tips in the next few days
on the m42 engine I have also removed the thermostat housing but the thermostat is still in there dispite my efforts to remove it.
Does the timing cover have be removed to get it off?
It's no big deal if it does have to as the covers are coming off for chain inspection just don't want to break anything...... So far so good

Didn't realise the thermostat only sits there! Got it off and the water pump too (much hammering after 48 hours soaking in wd40)
just need to flush the matrix then order the parts and refit plus the new coolant and the joy of bleeding the system.

Ta for the hints