Shop Talk

Service Intervals

If you’ve purchased a diesel truck anytime since 2007 you need to read your owner’s manual very carefully about oil changes


Back in the good old days you changed engine oil every 3,000 miles and that was that. Boy, have times changed. Now most diesel pickups have extended the oil changes out to 5,000 miles in normal service.

The caveat is manufacturers have added so much towing and handling capacity to today’s pickups that some of them now have stipulations about “severe service.” If your jobs or driving style meet these severe-service criteria – as detailed in the owner’s manual – those extended service intervals may not apply.

There’s also a new layer of technology on diesels manufactured after 2007 that require a new type of engine oil.

Don’t be a SAP

The new emissions-compliant diesels since 2007 require lube oils that are low in sulfated ash, phosphorous and sulfur. These are called “low SAPS” oils.

Failure to use low SAPS oils will cause your diesel particulate filter to fill with ash sooner, and cleaning the DPF can be an expensive maintenance item (See “DPF Cleaning” on

Thanks to increased turbocharging and EGR rates, the new engines also run hotter and put more soot into the combustion chamber. To combat this the oil companies developed a new and more robust oil formulation, the American Petroleum Institute’s CJ-4 standard.

In addition to being low SAPS, CJ-4 oils offer better heat and oxidative stability. It’s critical you only use oil that has the CJ-4 or higher rating or the engine warranty goes down the drain with the used oil.

Synthetics extend service

Better oils and better engines are the reason oil-drain intervals now sit comfortably at 5,000 miles in some situations. But does that mean you can go further than that on full-synthetic or partial-synthetic oils?

The moment the automotive OEMs say “yes,” we’ll say “yes.” But for now, they say “no.”

Synthetics and partial synthetics are superior oils in many ways. The base oil molecules are more uniform in size, thus reducing friction inside the engine.

They’re also great for lower viscosity formulations (such as 5W30), which is essential when you want to start your diesel in temperatures below about 15 degrees Fahrenheit.

But what all diesel engine oils share in common when it comes to longevity is their low tolerance to soot.

It’s critical you only use oil that has the CJ-4 or higher rating or the engine warranty goes down the drain with the used oil.

And there’s the rub: Today’s EGR engines create more soot, and although a lot of it is controlled by DPF filters and other technology, a certain percentage of the soot generated in the combustion chamber inevitably winds up in the oil.

Are the premium priced full synthetic oils worth it? It’s a question we get all the time. If you buy your lube oil by the barrel to maintain your dozers, backhoes, skid steers and the like, you need to do a careful cost-benefit analysis.

But, if you’re maintaining a personal truck or just a few trucks used in your business, synthetics can be your friend.

A lot of you don’t always have time to change oil at the scheduled interval or you occasionally stray into severe duty territory, and here synthetics will at least give you a better margin of error.

If you’ve got $50- or $60-grand tied up in a truck you want to keep healthy for a long time, spending $100 extra for oil in a year makes good sense.

Older diesels

What if you have an older diesel engine with less or no EGR and less soot? Wouldn’t the more robust oil formulations enable you to extend engine-oil drain intervals?

In theory, yes. But theories have a bad habit of getting their rear end kicked by the big boot of unforeseen consequences.

Bad things can happen inside your engine long before you get the first warning sign. A faulty injector will quickly ramp up soot formation. Even the smallest coolant or fuel leaks into the cylinders can dilute your lube oil and compromise its effectiveness.

It’s for reasons like these that truck manufacturers err on the side of caution when setting oil drain intervals; stick to the “severe service” recommendations in the owner’s manual to be safe.

Sample that oil

If you’re just dying to extend your pickup drain intervals we recommend you do so only if you set up a regular program of pulling sample of the oil and sending them to a lab to be analyzed.

This will cost you $15 to $25 per test – almost as much as a DIY oil change – but the benefits are well worth the cost.

Polaris Laboratories, Blackstone Laboratories, the Oil Analysis Lab and Herguth Laboratories are just a few of the pro labs around the country that offer such services.

The presence of coolant, fuel, excessive wear metals and other contamination can alert you to engine problems before they become expensive or catastrophic failures. Make sure your lab looks at soot formation, fuel and coolant dilution in addition to the standard tests.

And if you use biodiesel on a regular basis, an oil sample should accompany every drain interval. Pure diesel atomizes into uniform droplet sizes in your cylinders, but biodiesel often comes out of the injectors in larger droplets.

The result is a less than uniform fuel burn, more unburned fuel in the cylinder and the lube oil, leading to accelerated wear problems and loss in fuel economy.

Many oil companies will give their big customers free or discounted oil analysis as part of a value-added program for the heavy equipment and trucks. If this is you, it couldn’t hurt to ask for free oil analysis on your pickups as well.