checked my water level today on my 93 wrx and when i lifted the yellow lid there was a layer of brown muddish style stuff? as the photos below show, any ideas what causes that? cars booked in for a serivce in 2 weeks.





Borich

 

I got the yellowish stuff on mine.I flushed out the old coolant,cleaned out the yucky stuff and poured some Castrol Longlife Coolant which is blue in colour and tap water.After a few weeks the yellow stuff is back.I have seen the same thing on most of the cars at the dealer w/shop.Must be a normal phenomena.