Auto-rx is a natural based cleaner. It doesn't contain solvents, harsh cleaners and what not to clean engines. That said, it's a slow but very effective cleaner and don't worry about oil thinning as you would associate with OTC cleaners since ARX doesn't contain harsh cleaners. It cleans as you drive your vehicle. It's primary purposes are to help stop oil leaks by way of reconditioning seals and gaskets, remove sludge and then suspending the sludge(I think?) and stop oil consumption. Though if your trying to remove varnish, LC ( Lube Control) would work better for this as it contains solvents but to a point.
Like oilboy123, I am not one to promote this product. I only honestly state what I know and facts,,,,,,AR