At the moment, there are certain used car dealers who are being accused of massive manipulation of the speedometers. Apparently, every third used car sold is affected. In the past, or perhaps still today, they were also accused of other misdeeds.
Apparently, cars with damaged engines were being bought and then resold as being undamaged, without even having looked at the engines. Apparently, all that was done - in most cases with the engine still in the car - was to remove the oil pan and the cylinder head and after loosening the con-rod bolts, replacing the oil scraper-rings with so-called PC-rings.
For a long time, this was considered to be a secret tip, indeed, that's all it was, just an attempt to pull the wool over the buyer's eyes (see video in part 1). It's all about reducing the too high oil consumption, by installing multi-part rings, which so cleverly fit themselves into the no longer quite cylindrical sleeve, that substantially more oil is scraped off than before.
Indeed, because the buyers of used cars only seldom carry out a longer motorway test with a performance check, do they notice the still existing loss of compression. As far as the crooked dealer is concerned, it's a case of out of sight, out of mind.
Oil scraper-rings with a customized fit have been around for more than 60 years. They are always multi-part, made up of metal bands and a so-called expander-spring. After all, without the pressure of the rings against the cylinder sleeve, no oil can be scraped off. As the above examples show, they are also installed in new engines to reduce the oil consumption when wear starts.
In the meantime, unusually low oil consumption can often be noticed. Thus e.g., a Diesel engine which has been driven moderately, can certainly achieve its 30.000 km inspection still using the oil which was filled in by the factory, without additional topping up. 02/15