I've heard this argument about Universal grade oils effecting catalytic converters and I don't buy it with one POSSIBLE exception. If an engine is so worn out that it is burning oil, then there MIGHT be a possibility of this being the case. But if an engine is that worn out, burning ANY oil will soot up the cat.

An engine in good shape and NOT burning oil is not ingesting it, thus, how does it effect the cat?

I use Chevron Delo multigrade in everything on my place except my C240. Since it came with synthetic, that's what I stay with.

I have NEVER had ANY issues with catalytic converters on ANY of my vehicles and my family and I drive A LOT.

All that said, I don't propose that joetam use Universal Grade permanently, only to clean things out. But now that I hear that his engine only has 15,000 miles I can't imagine that it is gunked up. I expect that changing to a little heavier oil might be his solution.

Have a great day,