Conventional oil = semi synthetic?
- Thread starter stangguy
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All 5Wxx oils seem to be labeled as syn-blend now since API SP/ILSAC GF-6A went into effect, the 10Wxx and SP rated monogrades are still labeled conventional but are probably made with group II base stocks, which I guess you could call "semi-synthetic"
AutoMechanic
Site Donor 2026
Unfortunately I think all of the 5W and below are synthetic blends now. Fortunately 10W and up is conventional.
Synthetic is bad vs conventional because?
old school oil for old school cars, Danno 
No, Automechanic changes oil early on all his cars, some don't do 200 miles on an oil change. Synthetic or semi-synthetic makes no sense as itá yet another added cost.
No, Automechanic changes oil early on all his cars, some don't do 200 miles on an oil change. Synthetic or semi-synthetic makes no sense as itá yet another added cost.
AutoMechanic
Site Donor 2026
I don’t feel it adds any benefit really plus my cars don’t get driven a lot and I change the oil every 3000 miles or 3 months. Except my moms car we do 5000 or 5 months because it has to have synthetic.
OVERKILL
$100 Site Donor 2021
Wait, so if you only get 500 miles on in three months you change the oil?
Dude, that's a shorter OCI than what people did in 1950.
Most all conventional oils are group II. Group I conventional oils are rare these days in engine oils in the US and the oils that do contain group I are usually syn-blends with 15-30% group III to give it some thermal stability.
Given the price of synthetic oils these days, there's not much argument for sticking with conventional. The exception might be a drag racing engine spraying a lot of nitrous with low oil temps where the higher pressure-viscosity coefficient of conventional may be desired.
Some 5w30 and 10w-40 conventional oils may contain a small amount of group III if they want to reduce reliance on viscosity modifiers and allow them to more easily pass API tests. I wouldn't be concerned about it really. For just a few dollars more, I'd buy an oil that's all group III or higher.
for the cost of typical fake synthetics aka group III why not use them!!! lots of benefits for sure even if changed more than recommended, even brand names like quaker state ultimate durability, about $4 a qt in 5 qt containers are cheep!! UNLESS your ride DRINKS oil like my dads old 50 Packard the needed oil at almost every gas stop, only a kid then but remember the blue smoke screen it left!! he got rerefined oil in glass containers with the metal spouts or was it used oil???????
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What does mom drive?
AutoMechanic
Site Donor 2026
2017 Camry
Yeah I think a lot of conventional oils with viscosities 10w30 and higher are truly conventional. I buy Rotella T4 15w40 for my motos. I've looked those labels up one side and down the other. I'm sure Shell would jump at the chance to label it as semi-syn, but nope. T5 is semi-syn and T6 is full synthetic.
SN+ 5w30 and lighter had to be roughly 50% group III to meet spec unless it had the legendary Exxon Mobil mystery sauce base stocks. I would expect this to increase with SP.
I know warren coastal motor oil is synblnd from 5w20 to 20w50. Guess it depends on the brand.
Jackson_Slugger
$50 Site Donor 2022
Why "unfortunately"? They charge you the same either way. I also doubt many 10w30's and even 40's don't contain some GIII nowadays, since it has been stated that it is almost more economical for companies to meet specs and that they have a lot of GTL laying around (SOPUS at least)....
AutoMechanic
Site Donor 2026
I don’t feel synthetic is a better buy or anything. I have done the same things with conventional that I have with synthetic like cleaning a sludgy engine and stuff so I don’t feel the synthetic is worth the extra price. Based on what I have seen there is a price difference.
In the US, yes, in 3rd world countries, no.
Stop wasting oil then.
AutoMechanic
Site Donor 2026
I’m not lol. My dad won’t let that one go past 5 months or 5000 miles neither will I. We use Mobil 1 in that one.
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