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- Oct 19, 2025
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I think as most of us are, l am interested in stretching out the oil change as long as we can... While keeping the rings clean, a good viscosity, no sludge, low to no fuel dilution... Etc.
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‘Regular’ Mobil 1 now rated to 15k miles
- Thread starter addyguy
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AMSOIL Signature Series has a proven track record for extended OCI.
I've done it so many times, I don't care to remember. None of the engines ever "complained".
Edit: It wasn't "boutique oil".
Yea, because it would make a big mess all over the seat, when the jug started leaking.
Of course this depends on price of oils being used / compared and lab pricing.
I can share in my specific case, (and without naming any names):
Yes, changing every 15k w/ combined used oil analysis costs less than changing every 3k.
Bump to 5k and it's not even a comparison anymore. The 5k is much much cheaper than a 15k+used oil analysis.
You running TGMO for 15k??
No, 5k. Compared to a more expensive "Boutique" at 15k
TGMO at 5k is cheaper than boutique at 15k? (Just confirming I understand you.)
I can get AMSOIL Signature Series at like 10.50 a quart if you get the case of 4 gallon jugs. So you'd have to get TGMO at 3.17/quart to break even, and that is spotting you a Denso filter at $3 apiece. You might be able to get that on sale. On one hand you're running a conventional, and the other you're running a top of the line product.
Boutique at 15k including the UOA? Yeah it's cheaper, by a lot.
I actually forgot to add the UOA cost into that quick math. So I think that a boutique for 15k is more expensive than your TGMO example now.
Edit: with my back of the envelope math, 5k OCIs with OEM Denso filter x3 would breakeven at 5.50/quart with AMSOIL Signature Series at 15k with a $10 filter (assuming better filter to handle 15k miles). So if you can get a jug at $27.50 that would be equivalent to boutique for 15k.
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Deposits in piston ring lands has become a hot topic. Will increasing the OCI by another 5,000 miles help with that?
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Given that it's the lightest fractions that flash off earliest, I'd think, within reason, that extending the OCI, assuming there aren't other mechanisms seriously impacting the volatility of the lubricant, like massive amounts of fuel dilution, would indeed aide in reducing the propensity to produce deposits in areas like the ring lands.
So, as we all should know by now:
1) Depends on the oil
2) Depends on the conditions seen
Honorable Mention:
Getting the Fear Based “Mileage Alone is the GOAT” basis out of one’s tormented soul; and letting the above instead rule decision making
Now, let’s do that over the life of vehicle ownership and in context of owners that prefer to keep vehicles for said life of equipment.
Let’s ballpark 300k miles of ownership. AND clarify that this vehicle is driven mostly highway miles of a decent commute (10+ miles one way)
So, up to full temp per trip? Yes. Smaller % of stop n go? Yes. No meaningful fuel dilution across used oil analysis? Yes.
A handful of $40 used oil analysis. Let’s say done 9 times; in batches of 3 consecutive, one batch done around 50k miles (as engine is well past broken in) and by 100k you’ll have good data on 3 of those 15k mile UOA. Obviously, if conditions got extreme short tripped and severe fuel dilution (5% or more etc) and severe oxidation even with proper lube? You stop and shorten the interval. Any concerns Valvoline Restore and Protect is there for those 5k mile intervals to clean up any residual deposits if they occurred due to worsening conditions driven (assuming a simple daily driver without need for more demanding specifications; Valvoline Restore and Protect is on many folks short list these days)
However, if that first batch of 3 checks out we simply do that again approaching 200k and again late in life approaching 300k to spot potential problems not related to the oil. Head gasket leaks? Still tracking fuel %? Any uptick in possible contamination entry or soot/insolubles? Etc
Thats $360 in used oil analysis. We obviously monitored for condition changes that would dictate a deviation to shorten the interval along the way.
15k mile OCIs span over 300k; so 20 oil changes, and you still come out ahead of changing it every 5k; which would require 60 oil changes. Thats 3x your time.
EDIT: Forgot to show the math for sake of the argument, call the 5k intervals $35 in oil + filter cost and 15k intervals $100 oil + extended life filter. $2,100 for the 5k intervals over 300k vs $2,000 for the 15k intervals. $2,360 when you add in the 9 used oil analysis at $40 a piece.
$260 more spent in this equation in overall cost paid but you save yourself 40 extra oil changes worth of downtime! We’re likely talking 10+ years here. $26 a year difference at most; assuming more used oil analysis than most would use? I don’t mind paying $26 for my time saved.
Again, the right oil for a vehicle that allows for 15k extended drain intervals? 15k is the correct decision when you get data to back it up.
This does underscore the fact you can’t blindly do this; which can in fact get some engines into trouble. Just for example some Toyotas recently have blindly gone to 10k miles on bulk dealer oil; per the owners manual, and running out of oil between intervals later due to crazy consumption and when outside of warranty. So, it happens that it’s not as simple as a mileage recommendation.
You need good UOA data, coupled with good oil selection and conditions driven taken into consideration to begin to extend it out.
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For the money I’ll stick with Mobil 1 ESP 5w or 0w-30
When are they gonna put 'Lifetime' on the bottle? 
The Mercedes metris requires Euro spec oil but specifies 15k mile ocis. I've recommended Mobil 1 Full Synthetic 0w40 to owners, but told them to change it at 10k (I think the 2L engine holds 8qts). Maybe if Mobil 1 starts putting 15k on the bottles I'll change my recommendation, but 10k is already plenty long!
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The Pennzoil Platinum that I put in recently also places the 15k claim on the label. This was not Pennzoil Ultra Platinum.
I saw that the Mobil 1 Advanced Fuel Economy (API SQ) oils are 15k rated as well.
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