I put in a new engine about 2 months ago.
It had a failed headgasket and was rebuilt ( admittedly not by me )
I ran the engine gently , and noticed a small amount of "goo" in the expansion tank.
i cleaned the expansion tank out - but the "goo" returned.
The car does not have any signs of HGF - no missing , idle issues , use of water or smoke. No overheating either.
Could it be crap left in the engine from when the HG went bang last time ?
If so - what's the best way to flush it all out ?