[JimmieD]

I currently use the Valvoline Premium Blue diesel oil per Cummins spec, with spec'd Fleetguard filter. However I just got a nice old bypass filtration unit and will be using a NAPA 1503 in it at first, to aid in total cleaning of oil. This will be in addition to the stock spin-on. this bypass unit uses a drop-in filter.

Next step is to change over all lubricants to Amsoil. From my research they have an excellent product line with proven performance. I still need to find out which bypass filter cartridge has the finest micron rating. These bypass systems are the final answer for a 'keeper' engine as they're proven [SAE analysis and testing] since the 40's to greatly extend engine life. Cummins even spec'd them as standard equipment on many of their engines. Under the right circumstances your oil will last for the lifetime of the engine with only 'makeup' oil added at filter changes! Bypass also removes diesel soot which other filters cannot capture. When soot particles are clumped together they're very bad news for the engine's guts, so bypass is the answer.

 

[JimmieD]

On the bypass systems you're getting into a pretty large area of factors. There's 'Bypass Spin-on' that uses small micron filters, such as the Amsoil and others. There's the bypass that I use which is a cannister type, not spin-on, and uses cartirdges inside filter housing. It's about 10" X 4" and uses maybe a quart or so to refill cannister with a filter in there, haven't installed and filled yet. My cartridges run between $8 plus shipping or $12 at the counter from NAPA for a WIX filter.

The very best for ultimate filtration is a toilet paper element filter. If one has a brain and uses good sense they're not really messy to change out and refill. Nothing matches the micron filtration rating. One uses a single TP roll, Scot 1000's, another uses 2 rolls, and another huge thing uses Paper Towel rolls.

You can use an auxiliary mount for a spin-on cartridge for a bypass, or there are dual spin-on adapters with one cartridge for normal oil filtration and the other for bypass. There are also adapters that are only bypass, or only normal spin-on oil filter. Anything you want is readily available. If you post specific needs I can direct you to mfgr's or more info on that type. I don't sell products, by the way.

 

[JimmieD]

Just depends on what you want to do. The full flow system is often needed by the engine design, and a change to bypass directly in this system wil fry the engine for oil starvation. The combo units address that issue by allowing normal full-flow to remove larger particulates and by pass for the itty-bitty stuff.

Some combo systems are grossly over-rated in that their bypass elements don't have a fine enough micron rating to really do the job. You have to check that closely to KNOW what you're getting. With spin-ons in a combo system you can tailor it to suit with whatever filters will fit the threaded adapter of full flow and bypass sections.

All units require an oil restriction somewhere in the bypass system. This siphons of a small portion of oil for super cleaning, while the full flow system also cleans and supplies oil galleries with needed lube. 99% of the time you need both, unless the engine is specifically designed to use bypass only, like some Studebakers of the past.

Using a separate stand-alone bypass system can be much cheaper. You can plumb it in where and how you want and decide on the exact filtration you want. Either system can work very well if you do your homework on what's actually offered, beyond hype and BS, and cut to the chase on actual specifications. Even within the same mfgr.there can be BIG differences between their products, so call the tech lines or whatever and pick brains until they tell you straight up. Then compare specs and decide what's best for you.

The add-on TP filter types offer the best filtration to smallest micron rating, but several spin-on catridge units go down to 3 to 5 micron which is plenty to really clean your oil.