I have found 250C stinks like ivery soap for a few days and then has vary little stink to it .... I used the E206 before changing to 250C and it was great on steel but was crap for alum parts ,,, The E206 is a old school super hi oil coolent and makes a hell of a mess
do you test the coolant before adding to it ? the 250c has vary little carry off and I only use about a 2% mix to top the tank off and I keep the tank right about 7% mix .... If I am going to run steel parts I just don`t top off the tank for couple days and let the mix get up to 9 or 10% and it works better on steel ..
Like all coolant you have to clean the tank out every few months and filter the coolant to keep it clean .. I wire the legs shut on a pair of old blue jeans and hang them over a clean trash can then just pump the coolant thru the pant legs ,,, best filter I have found