Oil Sample Analysis Results - 2010 GMC Terrain Long-Term Road Test

2010 GMC Terrain Long-Term Road Test

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2010 GMC Terrain: Oil Sample Analysis Results

September 30, 2010


Just over a week ago, I took an oil sample from our 2010 GMC Terrain and sent it to Blackstone Labs in Fort Wayne, Indiana, for analysis. Our GMC's built-in oil life monitor was telling us that the oil could last something like 10,000 or 11,000 miles, so I pulled 3 ounces from the crankcase when the oil had 5,731 miles under its belt (and the engine had 15,000-odd miles) to see what the oil had to say for itself.

In short, Blackstone told us we should change the oil sooner rather than later -- within the next thousand miles. Not every time, mind you, but this time, at least.

I talked to Ryan Stark of Blackstone Labs to understand why they're telling us this. Those are my scribbled notes, not his.

First, a recap of the basics:

The last change was done by a dealer at 9,615 miles, 5,731 miles ago. This was also the first oil change, as we had followed the owners manual's advice and keyed off the Terrain's on-board oil life monitor for the interval.

We have no way of knowing exactly what sort of oil the dealer put in, but the oil filler cap says that 5w30 is the right stuff. They did affix a tag to the windshield reminding us to come in 3 months or 3,000 miles. This little upselling gem set me off and got me digging into the subject.

Here are the highlights of Blackstone's results:

The average oil change interval for this engine family is 5,195 miles. But that's not the suggested oil change interval, by Blackstone or by GMC. This is nothing more than the average oil mileage at which all other Ecotech 2.4 samples were sent in to Blackstone for analysis. It's a measure of owner behavior. We can breeze right past this and look at the results themselves.

Our Terrain's oil viscosity measures 5w20. It's impossible to tell if the dealer installed 5w20 or 5w30 initially, because Ryan said "it could have sheared down". He went on to say this doesn't matter too much, because the ideal viscosity range has more to do with the local outdoor start-up temperature. They don't see a strong correlation between engine wear rates and oil viscosity in their historical database.

Certain wear metals (they measure 20 different ones) were detected at higher levels than would be expected for the typical "broken-in" engine. Iron is as 47 ppm instead of 12; Molybdenum is at 178 ppm instead of 64; Silicon is at 18 ppm instead of 11; Copper is at 7 ppm instead of 3 ppm. Most of the others are close to the norm. But Ryan says this does not mean the engine is still breaking in -- he says that wear-in is over and done with in the first 100 to 1,000 miles of operation.

What Blackstone is instead saying is these break-in "residuals" float around in there and hide in nooks and crannies within the block and head, something the oil life monitor may not account for in all cases. Oil and filter changes are the best way to get the stuff out, and you want it out because it's potentially abrasive stuff. While every engine design behaves differently with regard to this tendency, Blackstone thinks it would have been better in this case if we had gone with 4,000 to 5,000-mile intervals for the first three oil changes before we started to follow the oil life monitor's recommendation.

TBN is the Total Base Number of the oil. Jim, Ryan's dad, reminded me you can't run a pH test on a non-aqueous solution such as hydrocarbons, so the TBN test is run instead to measure how "basic" the oil is. The Total Base Number is a rough measure of the active level of detergent dispersants in the oil, additives that are there to keep dirt and solids in suspension so they can be captured by the oil filter.

Our oil's TBN is 1.8, and the recommended minimum is 1.0. But Ryan wasn't too concerned about this because he likes to focus on the number right below it on the report, the Insolubles Percentage. Our IP is still quite good at 0.2 compared to a target of 0.6 or less. He says that this tells him the detergent and filter are still doing a good job, whatever the TBN happens to be. From an insolubles and filtration standpoint, 10,000 miles still isn't out of the question.

He says the TBN test is more applicable to diesels, and it's more of a legacy test that some customers want to see. Oil (and detergent) sales and marketing efforts of the past used to tout their product's TBN as a measure of superiority versus the competition. (Remember Grandma's "Basic H" all-purpose cleaner? - I didn't until just now). They still run the TBN test for those that request it, but it's not part of the standard Blackstone test protocol. The Insolubles Percentage test, however, is standard.

The bottom line:

Ryan says the level of wear-in residuals is not alarming for an Ecotec engine of this relatively young age, but they are higher than he'd like to see. Blackstone suggests that we change the oil to get the levels down sooner rather than later. That said, the oil life monitor has not led us down the garden path into serious trouble. Oil life monitors are fine, he says, but the break-in residual issue leads him to recommend a more traditional timetable of 4,000 to 5,000 miles for the first two or three oil changes.

It's likely that Blackstone's conservative position on this comes from their typical customer -- fleet managers and trucking companies. These folks don't just want 100,000 miles of engine life, they want 300,000 miles and up, if they can get it. But they also don't want to spend any more money on maintenance and downtime then they need to. Strategic maintenance with an eye toward ultra-long engine life is their goal.

What's GM's take on these results? We'll see what we can find out and let you know.

In the meantime, can you guess what comes next? That's right, a GMC Terrain DIY oil-change post. But this one is going to be a bit different from the others I've done in the long-term fleet. That's as much of a hint as you're going to get.

Dan Edmunds, Director of Vehicle Testing

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