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Oil Changes - Mileage or Time? Blackstone Lab says Mileage is what matters


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Oil Changes - Mileage or Time?  Blackstone Lab says Mileage is what matters


Blackstone Laboratories Podcast - 5/25/2020


3:45 to ~9 minute mark most relevant for cars



Oil Change best to be done on mileage basis NOT by calendar

Calendar time alone does not cause oil to breakdown in the crankcase of engine - (unless open breather) - recent engines are sealed

Transmission oil also does not deteriorate with time in the tranny, focus on the miles.

Transmission oil breaks down as it is used




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Keep in mind that manufacturers need to move product, and much of their downstream customer base is cash constrained at present. Manufacturers will be dumping old inventory (via credits to the garage/service provider), to bring customers back in.


In most uses, synthetics have the longer life, a wider temperature range of use, and cost less/mile driven. It is more expensive than regular oil for a reason; but in today's economy, a manufacturer will begrudgingly eat the difference to move old product. Use the opportunity to upgrade.


Does it really matter? If it seldom gets below -10C where you live, and the driving is primarily commuting - probably not. If -35C is not unusual, or the vehicle often has to haul heavy loads - it matters.






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Most modern engines with modern oil can go way longer than the manufacturer's recommended oil change intervals. I look at oil changes during the warranty period as primarily an investment in maintaining my warranty. After the warranty is over, I space them wider (and only by mileage).


There is an agency problem. Most consumers dont check the recommended service interval prior to purchasing a car, but the service interval makes a big difference to dealer profitability. So the manufacturer has an incentive to keep it shorter than necessary.


IIRC, once BMW started including oil changes the service interval increased quite a bit.

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I usually follow the manufacturer recommendations on mileage, not always time.  I may change the oil based on time depending on the type of driving (short commutes).


The oil not just lubricates but absorbs combustion byproducts.  The detergents lose effectiveness over time, but should be mostly correlated with mileage, not time.  I would think the time component would matter more if all of the miles driven were while the engine is warming up (short commutes vs long distance driving).

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I usually go 50% over the recommended mileage, and disregard the time factor.


Also, tolerances between moving parts will decrease as temperature increases & you don't want to start banging away without a warmup.


The last 3 vehicles I've owned have always gotten warmed up before driving.

I just wait for the temp gauge to go a bit above the 0 mark.

During Summer it takes no time & Winter a few minutes.


When I worked offshore, we would occasionally go over the recommended hours due to the nature of our work & I'd notice our fuel consumption would start increasing dramatically.


Apparently sludge develops, which decreases viscosity.

The reduced flow degrades lubricating qualities & causes a decrease in cooling ability.

The resultant overheating can put a lot of stress on hoses, seals & bearing surfaces.


We always sent samples off for analysis & the results were very useful in spotting problems before they lead to a failure.

(I've been saying that I was going to do this with my truck but so far it's all been just talk.)


If you drive in dusty conditions or have a lead foot, you should probably stick to the recommendations or even change a bit sooner.

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