Hy.I am from Croatia, Europe. I have elantra 1.6 16v,2002 year, with 80 000 km.On cold starts i hear knocking under valve cover, that lasts until engine warms up. I suspect on sludge in the valve lifters. I was thinking about usingCRC engine flush. Has anybody usedengine flush, and whatare the experience with engine flush. Does anybody knows reason for that knocking under valve cover.
Thank you for answer.

 

I wouldn't use an engine flush. Many times theywill dislodge sludge only to have it block a oil passage. I would suggest using a thinner weight detergent oil.

Also, are you using Hyundai filters or aftermarket? If aftermarket, what brand?