My experience has led me to
480M Ultragard from
Primrose Oil Company. Add this product to your crankcase oil at 10% by volume i.e. if your crankcase capacity is 5.5qts, on your next oil change put in .5qts of 480M Ultragard and 5 quarts motor oil. The amount of additive recommended is an important factor to weigh as you want to avoid changing the oil's viscosity with too much oil supplement. For example, Lucas Oil Treatment directions say to add a minimum of 20% by volume and recommends you actually use 60% by volume. IMO these amounts will change the oil's viscosity and increase the potential of doing more harm than good.
A couple of big reasons I use 480M Ultragard is: 1) it doesn't stratify or separate from the oil it's mix with, as it chemically bonds to the oil. This greatly improves the shear strength and improves the oil's viscosity index. 2) It plates to the metal surfaces it's lubricating. This is huge as motor oil today contains very little, if any, zinc and phosphorus, a.k.a. ZDDP. This plating ability is particularly beneficial when you shut your engine off, as it leaves a protective coating on vital engine components and inhibits oxidation. This protective coating also acts as a sacrificial lubricant when starting your engine back up making it easier on your engine during cold starts. It should be noted that 480M Ultragard does not contain actual ZDDP anti-wear additives, however it does provide the benefits of ZDDP while being completely safe and beneficial for use with today's engines designed with emission control devices and after-treatment systems.
When it comes to fuel additives I've seen really good results cleaning fuel systems on the gas or diesel side with
406 Injector Perfector also from Primrose. Depending upon how clean or dirty your fuel system is, you may need to treat 2-3 consecutive tanks of fuel when first starting to use 406 Injector Perfector. After initial clean up, treat 1 full tank whenever you change your oil.
If you're looking for a quality every tank treatment additive that maintains cleanliness, prevents or
reverses phase separation and will stabilize your fuel when storing your boat, car, motorcycle, snowmobile, lawn & garden equipment, etc... use
Phaser 3000.
The Seafoam's, Sta-bil's & MMO's we've all tried at one point or another have little to no effect on today's modern fuel formulations and I seriously doubt they were ever actually effective. Although guys that work on carburetors swear by the cleaning ability of straight Seafoam when used at 100%. Personally I think they'll get the same or better results with straight up Isopropyl Alcohol considering that is 70% of what Seafoam consists of.
When it comes to Diesel Powered engines, either of the above fuel additives from Primrose will also work with however, neither are as cost effective nor do they include the necessary ingredients needed to provide the remarkable results you'll get from
5007 Power Klenz ID, also from, you guessed it, Primrose.
5007 Power Klenz ID boosts Cetane by 40 points (4 numbers), improves lubricity, thermally & oxidatively stabilizes diesel fuel, extends fuel filter life and dissolves & inhibits IDID's (Internal Diesel Injector Deposits) that cause injector stiction, among others.
Sorry for the lengthy post, but I hope some of this information has been helpful.