Header tank full of oil

chris-the-gerbil said:

As for cleaning the system most coolants are moderately alkaline and unless excessive amounts of base are added it wont attack the metal. I've had good results cleaning engines by using water dosed with a bottle of ammonia cleaner - it doesn't foam and will easily remove oils by converting them into soap. The coolant hoses and seals wont be attacked by it either. I wouldn't use any form of lye as this will go after all the aluminium in the system with great rapidity.

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Most coolants sit at around pH 10 (clearly it will vary from type to type dilution to dilution but for this discussion 10 is a good figure) - which to put in perspective is not massively more alkali than milk of magnesia, to put it into even better perspective again some shampoos can be as high as 10!

Your ammonia is about pH 12 whereas Sodium Hydroxide is about 14 - obviously then it is diluted so the pH will drop but on the scale of things ammonia is going to be a good 2 points behind - better!

Household ammonia is about 4M from what I recall, doing the maths sticks it at about pH 11.7 With dilution in the system it should be less as you say but it very rapidly attacks oil and gets converted into soaps. Doesn't take long either - I used about 500ml to clean out a friends K-series Rover and it was ready in about 5 minutes.

If you leave it in for any length of time with no oil present though it'll do a really good number on the radiator unless it's copper/brass so it's not one to go at with excess amounts but ive never found anything better for deoiling a cooling system.

just an update and a chance to say thank youto you for all the advice.it is indeed a rad failure . new rad that's been ordered £ 109 including vat and I will change the gasket down at the oil filter not sure the correct name for that gasket but it costs 40p also ordered an engine flush, I know it could have been done cheaper but its only 16 quid with same day delivery chucked in.
these forums are just the bees knees.

Hang around for long enough and you to can be a boring fcuker handing out the advice