When I worked rebuilding big diesel generators several decades ago the salesman lined up to sell bypass filters. They work very well (the filters not the salesman) and do clean a lot of the finer particles the direct flow filters can not. However after installing bypass filters we never altered or extended the interval for changing oil and full flow filter. The cost of changing oil and filter was and still is insignificant compared to braking down due to sizing a bush due to poor lubrication.
In a pleasure boat, I wouldn't mind installing one of them if there is time/ room and money but not with the aim of saving money on oil, but in order to keep the insides of the engine and the oil as clean as the first day. That is a good result, and change the oil as you would normally.
As per the magnets...well you*said it all. It is a scam like all the other magnets scam.
There is a magnet that you can apply to your thingy and it will make it grow bigger.
Now there is imagination for you. Someone must be buying those too.
Now if it makes the thingy grow...would it also make the fuel level rise? Now that is a claim worth mentioning!
-- Edited by Marc1 on Sunday 13th of December 2009 12:11:07 AM