HG failure after Saab valve fix?

Hi all,



I bought a MG ZR not long ago. Car was fine and I was a happy chappie. Two days ago I lost hot air too the heaters. I phoned a friend who is familiar with MG's and he suggested Saab valve had possibly failed, as the same thing happened to him and it turned out it was his valve.



So yesterday I purchased some OAT and bled the cooling system and then proceeded to dismantle the cooling pipes behind the block. After getting the Saab valve apart (fiddily job!) I could see straight through the valve and found a rubber type washer further down the pipe. I removed that rubber like my friend suggested and replaced it with a tap washer, had about 5/6 mm hole in it. I then reassembled it.



I did a coolant flush and then filled up the coolant system proper, all went well, took five litres of 50/50 mix and it bled no problem. Quite sure there wasn't an airlock. Started car again waited a few minutes whilst checking temperature gauge and coolant level and hot air was back, nice and toasty.



I checked my oil only yesterday after coolant change and it was fine. Checked again today, and found what looked like brown sludge in the oil cap and dipstick. I took some of the coolant out and had a look at it in a basin, there was a very faint slick across the top of it.



The heater is still working fine, I appear to have no loss of coolant, the temperature gauge is where it should be, yet I now have what appears to be the signs of HGF.



Was this just building up and me doing the coolant change finally released it? Was it maybe gathering in the heater matrix and my flush dislodged it? I'm not sure what to think as all was well yesterday, I thought this amount of gunk in the oil and dipstick would be gradual, bit stumped to be honest.

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