Note also that fluid ratings are not always “backward-compatible.” In other words, newer is not always better despite petroleum industry assurances. A manual gearbox that calls for GL-4 will not last longer on GL-5; in fact, some parts will wear quicker.

All brake fluids comply with Federal standards but DOT 3, DOT 4 and DOT 5 are not newer and better (5 is silicone-based, 5.1 is not). Engine oils are API-classed S for gasoline engines and C for diesel.

The newest diesel oil standard is CJ-4. Some long-term diesel owners have found the CJ-4 for ULSD/DPF engines doesn’t have the same levels of zinc, phosphorous and detergents, and is not as good as the CI-4 Plus that preceded it. Many oil companies don’t want to produce two oils, but if you can find it, CI-4 Plus is often regarded as better for pre-DPF-era diesels.

If your truck requires any additives, like those for limited-slip differentials coolants in earlier Power Strokes or some fuel stabilizing agents, the owner’s manual will says so. Otherwise, forget additives and put that money to better use doing routine service.

About filters

Almost every lubricated component has some sort of filtering device, from a magnetic drain plug to fuel filters. These are cheap insurance when the proper parts are changed at recommended intervals or during an associated repair.

In those cases where truck and engine come from different manufacturers (e.g., Cummins/Dodge, International/Ford) an engine company’s service provider may have better prices and parts availability.

“Proper” part refers to that named acceptable by the manufacturer (engine or truck); more than one diesel pickup owner has suffered an engine failure because the media from an aftermarket oil filter broke off and plugged a piston cooling jet, and warranty coverage was denied.

If a factory filter is $15, a cheap one $8, and an engine $10,000, which is the best value?

Two other parameters deserve careful consideration: clutch-pack limited-slip differentials and diesel fuel filters.

Fuel filters on newer diesel engines are critical. With pressures more than 20,000 psi, even the smallest contaminant can do damage (think what your pressure washer does at one-tenth that pressure), and parts are not cheap.

The thousandths-of-an-inch clearance in a crank bearing is huge compared to the tolerance in diesel injection, where writing on a part with a Sharpie means it won’t fit anymore. If you’re a do-it-yourselfer, don’t pre-fill a diesel fuel filter because your eye can’t see contaminants that could cause damage.

Limited-slips improve traction and are an inexpensive factory option considering the traction advantage over an open-diff. Nearly all of them require periodic service and an additive to work correctly. Forget the additive and they eventually become unlimited-slips.

This article was written by G.R. Whale, a contributor to our sister publication ProPickup magazine