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Background: first oil change @3000 miles (dino), second at 6000 (switched to Mobil 1), third at 10k, fourth (this one) at 15k. Plan to do 5k oil change/tire rotation intervals for convenience. I only average 8-10k miles per year and asked if going 6 months betwen oil changes was ok and if the interval could be extended even further (not that I really plan to, but it's nice to know). I'll probably send in a sample every 20k miles just for a check-up. I'll skip the TBN next time since I know it's good at this interval.

Here's the explanation key:
Understanding
Blackstone Laboratories' Oil Report
For Gasoline / Diesel Engines


Averages: The universal averages column is the average of all the samples we have analyzed for the particular equipment make and model. The unit/location averages column is your average wear for that particular type of equipment. They are both running averages and change with the number of samples we analyze.

Elements: Elements are quantified in the oil at part per million levels (PPM). This list shows the most common sources of the elements in a gasoline or diesel engine oil.

Aluminum: Pistons, bearings, cases (heads & blocks).
Chromium: Rings, a trace element in steel.
Iron: Cylinders, rotating shafts, the valve train, and any steel part sharing the oil.
Copper: Brass or bronze parts, copper bushings, bearings, oil coolers, also an additive in some gasoline engine oils.
Lead: Bearings.
Tin: Bearings, bronze parts, piston coatings.
Molybdenum: Anti-wear additive, some types of rings.
Nickel: Trace element in steel.
Manganese: Trace element, additive in gasoline.
Silver: Trace element.
Titanium: Trace element.
Potassium: Antifreeze inhibitor, additive in some oil types.
Boron: Detergent/dispersant additive, antifreeze inhibitors.
Silicon: Airborne dirt, sealers, gaskets, antifreeze inhibitors.
Sodium: Antifreeze inhibitors, additive in some gasoline engine oils.
Calcium: Detergent/dispersant additive.
Magnesium: Detergent/dispersant additive.
Phosphorus: Anti-wear additive.
Zinc: Anti-wear additive.
Barium: Detergent/dispersant additive.
Physical properties: Viscosity, flashpoint, % fuel and antifreeze,
% water and insolubles are all measured in gasoline and diesel engine oils. If fuel is present in an oil, the viscosity and flashpoint will often be lower than what was stated in the A Values. Insolubles are solid material that is centrifuged out of the oil. They are typically free carbon from the oxidation of the oil itself, along with blow-by past the rings.
TBN explanation:
Do I Need a TBN?

What is a TBN, and who uses it? In short, a TBN (total base number) measures the amount of active additive left in a sample of oil. The TBN is useful for people who want to extend their oil usage far beyond the normal range.

By comparing the TBN of a used oil to the TBN of the same oil in virgin condition, the user can determine how much reserve additive the oil has left to neutralize acids. The lower the TBN reading, the less active additive the oil has left.

An oil's function is to lubricate, clean, and cool the engine. Additives are added to the oil to enhance those functions. If the oil becomes too acidic, it will corrode the engine. A good TBN result, meaning plenty of active additive is left in the oil, is usually in the 6.0 to 14.0 range (depending on whether the oil is for gas or diesel engines). A low test result, meaning very little additive is left, is down around 2.

Scientifically speaking, the TBN is one of two "neutralization number" tests run on oils. The TAN (total acid number), which is used for hydraulic oils, is the other. The TBN measures the total basedity of an engine oil; that is, how much base (as in, a base vs. an acid) additive is in the oil to offset the deleterious effects of acids coming into the oil from combustion and other sources.

However, the TBN is not the only factor to consider when determining how long an oil can be used. If wear accumulations and insolubles in the oil build up and become abrasive, we would recommend changing out the oil, no matter how high the TBN reading.

Case Scenarios

Case #1
Joe Owner has a new engine and wants to determine how long he can keep a fill of oil in place. He sends in a sample of his virgin oil (with no miles on it) and a sample of his used oil (with 3,000 miles on it) for an analysis and a TBN test.

The virgin oil has a TBN reading of 12.0. His used oil has a TBN reading of 9.5, and his wear levels are fine. Joe decides to leave his current fill of oil in place, and resamples in another 3,000 miles. This time, the TBN reads 6.0, still an average amount, but his wear accumulations and insolubles have built up to a level that causes the oil to become abrasive. We recommend that Joe change out this oil.

Case #2
Jill Owner has a new engine and wants to determine how long she can keep a fill of oil in place. She sends in a sample of her virgin oil (with no miles on it) and a sample of her used oil (with 3,000 miles on it) for analysis and a TBN test.

The virgin oil has a TBN reading of 7.0. Her used oil has a TBN of reading of 5.0, and her wear levels are fine. Jill decides to leave this fill of oil in place, and she resamples in another 3,000 miles. This time, the TBN reads 4.5, and her wear levels are still low. Jill decides to leave her oil in place a bit longer, and she resamples in another 1,500 miles. This time, the TBN reads 2.5, and although wear accumulations are still normal, we recommend she change out the oil.

Do you need the TBN test in your maintenance routine? Only you can answer that question. We offer a TBN test on any gasoline or diesel oil sample for an additional $10
And my analysis (everything A-OK. "careful operation" :D Also note the remark on oil filtration; this is on the stcok oil filter):
 

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How much was the test?

Cool results
 

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Discussion Starter #5
Just recieved some more info. re: Mobil1's starting TBN from Blackstone for reference:

Mobil doesn't post the TBN's for most of their gasoline engine oils {on their website}. Mobil 1 typically starts out at around 12.5. We have found that when it is first used, the TBN drops fast and then levels out and stays around 4-6 for a while.
 
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