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Hagerty Employee

What's the real difference between synthetic oil and conventional oil? | Hagerty Media

Nothing ignites the vintage car discussion boards like the oil debate, and the hardest part of that conversation involves separating fact from fiction. Many long-held beliefs may not be based around modern science, but sometimes the knowledge to correct those false assumptions is hard to find.
Pit Crew

My consideration is that oil is made to a spec, sold to a marketer, and the marketer's label then affixed to the can.
There's nothing special about the can you buy in terms of the label, the reality is that you're buying a product made to a spec, so find the spec for your car and you'll be good. Meeting an SAE, JASO or other spec means that the additives make the product, not the base oils.
Thanks for nothing, Castrol, for ruining the distinction between "synthetic" and "mineral" base oils, but now with the right additive package, it hardly matters.
Pit Crew

Don't blame Castrol. Blame advancements in technology. Additives are hugely important. However, base oils make up 85% or more of the product. Shell makes base oils from natural gas (Gas to liquids) which are generally group III's. Many "synthetics" use group II base stocks in addition to group III's or IV's. The diluent oil which can be as high as 10% of the final product is typically group II also. Some specifications are controlled better than others. How many modifications have been performed to an "original" formula to pass all the tests required? How many times has that "formula" been tested before passing (including aborts)? There are many excellent engine oils out there. Don't be mislead by "synthetic", "semi-synthetic" labels. If you like/use a particular brand, good for you. The marketer has done their job. Look for the specification that your vehicle requires and make sure your product is licensed or approved to that specification.
New Driver


Unfortunately, the discussion does not deal with air-cooled engines (think Volkswagen Vintage Air-cooleds). These engines come without any filtration system--they use a "settling process" with a screen to aid in the process. Advantage or not, without the addition of a filtration system, synthetics likely won't gain much advantage and will need to be changed about as often as mineral oils. Add to this, the design of these old-style engines which fail to compare favorably with water-cooled engines and, esp, with the more modern engines. Mostly, we in the Air-cooled Community run the "better" Mineral Oils with additives, esp. including zinc for it anti-scuffing properties. Fortunately, for a great majority of us Vintage Vehicle owners, we drive our cars more carefully and selectively than we did when they were everyday transportation.

Discussing oil is as bad as starting a conversation on politics and religion.

Everyone has opinions and facts.

Much of what you want is what oil is best.

As being involved in the racing industry we have seen the best results under synthetic oils. Now if you keep with the old oils you are not going to blow up by using them.

Getting the right oil for your needs, understanding that oil and changing it based on needs and use is what matters.
New Driver

Many years back I had a high pressure air compressor used for filling scuba tanks ie 3000 psi I used Delvac sae 30! After I moved and sold my business I had some of the Delvac left over so I started using it in my old 1970 Chev 4x4 K10 w/350 v8 everything was ok for while then i had trouble starting and running rough! I was going to a school in Milwaukee for the phone company and had to drive to Chicago to take radio license test! Then drive back to Ashland. My truck just got harder and harder to start! It died on me at the Elgin IL oasis! It turned over ok but would not start! So there I was blocking a toll booth lane! Thankfully someone gave me a push up to about 35/40 mph and It started and I made it home without stopping! Running very poorly finally found out that the Delvac which I guess is for Diesel engines and has a high flashpoint was fouling the spark plugs(yup it was an oil burner) I changed oil and plugs and had no other troubles! I hindsight I probably could have put in hotter plugs but I was young and not very smart back then( I guess I’m old now( and still kinda dumb) but I’ve been using synthetic in all engines for many years without problems.

New Driver

So many factors play into both oils , I use both depending on the age of the vehicle on if it’s a motorcycle or car , also air or water cooled will play a factor !
Some of my vehicles are driven every day others are classic or vintage , either way I will pick and choose what is best or recommended !
Following the specifications on each oil brand plays into my decision ! I favor synthetic for my newer cars with the right viscosity for our region ! My older air cooled BMW motorcycles I use conventional oil , this is where we can get into arguments over what is best ! Some motorcycles bathe the engine and transmission together and require a specific oil for that application . the other motorcycles have transmissions separate from the engine , some are air cooled others are water cooled , again chose your oils based on this design .Temperatures will very greatly on a liquid cooled vs air cooled engine ! Your ridding style plays into how frequently you should change your oil I.e. highway miles vs stop and go in heavy traffic .... example : cruising Myrtle Beach in the summer on the strand , some have no idea how hot an air cooled motors get , it’s HOT !
The debate will continue but those in the know will do there best to use the right oils I’m sure !
Happy motoring and be safe everyone !
Intermediate Driver

I have owned, driven, and worked on older cars and motorcycles for a long time. Several times I have tried synthetic oils for my engines and manual transmissions. Whether the engines were fresh, or high mileage, the synthetic oils never seemed to work as well as conventional oils. The transmissions seemed to shift harder on synthetics, and smooth out when I put the conventional oil back in.
Now this is just my observation, but the results seemed to be the same each time I tried synthetics. The newer cars are designed to use synthetic oils, but if it has a carburetor and distributor, stick with conventional oils. Because "you can't fool mother nature" .
New Driver

Interesting article, but from what I'm seeing in the stores-it's either synthetic or a synthetic blend. I don't see any 'conventional' oils anymore. Is the synthetic blend, conventional with additives OR a mix of conventional and synthetic oils????

The real truth is Syn oils tend to deal with heat and breakdown better than any of the other natural oil. Heat is how it is distilled to start with. 


The real trouble today is that many of the additives have changed and the Syn oil has made up for their loss in some aspects and or to prevent damage to things like Converters and O2 sensors too. 


With Zink being removed it has brought a lot of change to engines. It is one major reason every thing is roller now vs flat tappet. Yes less friction but also no wear or break in issues.  Zink was killing O2 sensors. 


Add to it the Turbo engines. Most would not survive on Dino oil. The carbon build up is much greater today and it kills the oil line to the bearing if it cokes up. 

Same on many Direct Injection engines today. Engine all leak a little oil down the valve guide to lube it. Today no fuel is cleaning the valve and it can also coke up with carbon. The syn oils are more resistant to that and help prevent it. 


Low tension rings today also can carbon up and Syn prevents this. 


Oils need to be looked at like a socket set. No one single socket fills all needs but the same for oils as some applications need specific oil for a reason. Most modern cars are designed for Syn oils today. Most older cars can still use it some may not like it. Just depends on the build and needs.  


Because of this that is why we have so many different opinions and ideas. While some people may be off base others are just in a different place with different needs as there is much variation out there. 


All my vehicles and even my Generator are on Mobil One. I have used it for years with great results. They even have a high content oil for my one Flat Tappet car. 


Now if I an old classic that ran with a Castor based oil that would require a much different fluid and that is fine. Not everyone can get by on just one type. 


So stop arguing read up and learn what the oils are and best match your needs. Also keep up with the changes as some of the older oils are no longer around and you need to upgrade to a modern version. 


Lord knows how many customers I have had put in new cams wipe a lifter or two out and not understand the loss of some of the phosphate's and Zink that protected their cam in break in and performance. 


I like it better when the writers focus on the lead, zinc, and other topics of the crankcase issue for the pre/post 80s/90s split. Real synt oil, developed/sold to "us" in the early 70s, was not oem specified till engine tolerances got really tight. Let's hear more abt WHICH engines do best w/WHICH products.
I don't feed my '66 bronk w/the same stuff I do my 3rd gen (made w/consideration toward my aged body's limits) Focus...
New Driver

When I was an Engineman in the Navy I went to A School for Lubrication and. Lubricants. Learned all about this Subject.
Unless your at the North/South Poles or in Space or at the bottoms of the Oceans there is no advantage of synthetic lubricants. Your just wasting your Money.
On board Ships they never Changed Oil,Ever we had a centrifuge for Cleaning Oil.
Oil doesn't go bad it just gets contaminated/ Dirty. There's 2 types of centrifuges #1 was The Sharple's Centrifuge which would clean the used Oil(even know it was Black,,,,,,,,it was clean. No Gritty feeling)#2 was The Duvall Centrifuge which was more complex it would seperate by weights. And all types of lubricants, We recycled all lubricants.
Now the only thing that both types of centrifuges couldn't do was seperate synthetic Oil from conventional Oil. So if you buy a Generic/Store Brand Oil that's most likely made from recycled Oil guess what??? It's a Synthetic Blend already!
I've been building Engines for 45 years and I swear by Tech Oil sold by Wal-Mart.... There brand which is recycled Oil and never had one bit of trouble with it. Synthetic Oil isn't something new,,,,,,,It was invented in the 40s by the Nazis. So unless you plan to drive in Space/ Bottom of the Ocean or to the Poles? Stay with Conventional Motor Oil.
New Driver

I’ve been using Rotella 20-50 in our 58 TR-3 will much less leakage and hopefully the zinc helps the tappets.
BTW I found an ancient bottle of unopened Pennzoil 30w dino oil sitting in the garage for years which had 1/4” of ash/dirt/stuff on the bottom. No idea what that is.
Intermediate Driver

For 20 years I did a 250 mile daily commute , often in bumper to bumper traffic for the last 40 miles on the inbound trip and then the outbound at the end of the day . Most of this travelling was done in a 2001 Sonoma witha 2.8 V6 5 speed. When the warranty had expired, I began using Lucas stabilizer with conventional 10W30 and changing it every 4000 miles. I ran that truck until the frame rotted out at 680,000 miles . The engine was still running fine. I replaced that truck with a 2011 Kia Sorento with a 6 cyl, that car now has 220,000 miles and have used the same method with the Lucas. I see no need to change anything at this point. Seasons Greetings everyone. 🙂
New Driver

Good morning, I read through all the posts associated with the link and found it interesting nobody mentioned oil analysis as a means to determine if an oil is performing well. That is such an important step I'm shocked it was not discussed.

Some twenty years ago I attended a technical conference put on by Joe Gibbs Racing at De Anza college. The usual sort of presentation was made about ZZDP and additives and base stock, but then Joe Gibbs' (son?) who was the lead presenter gave some interesting history about base stocks and the petroleum industry. His new (to me) information was: historically some base stocks were chemically different than others depending on the geographic area they were mined in. The refining plants were constructed to crack those molecules into shorter chains and reassemble them into a base stock product for sale to various regional marketing firms. Because the amount of cracking and re-assembly of a petroleum molecule was limited by existing technology (1920's to 1990's) there were actually differences in the characteristics of finished oils and their performance in various uses. Various additive packages were developed to "help" specific base stocks do better.

Financial factors in oil production were significant in determining the final product's price. Crude oil was shipped from wells to refineries based on final overall production costs while being limited by refining plant capacities and capability. Not every plant could refine every well heads production, so quality of a finished product was somewhat variable and somewhat regional. To create a more consistent product nationally and worldwide refinery capability was enhanced to the point where (currently) almost every refining plant can now crack any raw petroleum into elemental hydrogen and carbon then "build" an "oil" from scratch. From this point of view all oil is now synthetic because virtually none of the natural chain structure remains when an oil is created that way. And refining companies can buy depressed price crude from distant sources, as needed, while knowing they can fabricate it to whatever standard it needs to meet.

However it costs more money to create a complex hydrocarbon chain than a simple one so when a modern base stock is formulated, if it resembles a short chain natural molecule, it can be sold as "conventional oil" at a cheaper price point vs. the highly complex and developed long chain molecules sold as "synthetic". After this two factors change a base stock into a marketable product.

Legal requirements mostly related to meeting EPA standards and manufacturers requirements to meet performance goals. Conformity to both is done by changing the additive packages and by way of declarations. If, for example, you don't advertise the oil as meeting any particular manufactures use standards then you are free to formulate it to meet other business requirements, like being low in cost. Or if you mark the oil "not for use in pollution controlled vehicles" then you don't have to remove or add (or not add) certain chemistry which otherwise would be necessary. This is how Joe Gibbs racing was making and selling their product line.

They would buy highly refined and specifically tailored base stock to which they would add specific additives helpful to racing and competition. They would not make any attempt to meet vehicle manufactures specifications and would mark their product for off road use only. This went on for a couple of decades until some states rewrote the laws about oils to limit how much of some chemicals a finished oil could contain no matter how it was advertised or marketed.

The circumstances of increasingly limiting oil formulation possibilities continues today and is now limiting some older engines to vintage or display status unless either the engine or the oil used is modified. It is possible to buy oil additives in separate bottles to "finish" the blending process which manufactures are banned from doing. However a person doesn't know if they need to do this or not unless they test and analyze their oils performance when run in a specific application.

The difference between organic and synthetic oil? About two bucks a quart! (rim shot) I'll be here all week....

Here in New England engines always outlive the car no how you neglect them. I change my engine oil and filter when A) the level is low enough to justify it or B) when I'm out of cutting oil for the lathe and mill.

Hey, that was MY line, "...about $5 a quart!"

I started using a synthetic, EON (later NEO; some kinda legal thing...) in my new '75 Cosworth Vega after consulting with an Engine Builder friend of mine, concerned about the 'silicone-lapped aluminum block'...

We're STILL Friends...

Over the years, my interest in Synthetics ebbed and flowed (pun intended), as I have Never had an oil-related failure using either high-grade Natural Lubes or Synthetics. I've used Castrol in my Brit Bike, Kendall GT-1 in the Race Cars, along with Amsoil and Red Line Products. Street Cars use Quaker State, Diesel Hauler Shell Rotella, and all seem very happy with my selections. My one complaint is in regard to early Mobil 1 products. I had NO LUCK with their Gear Oil; it burned, stank like HELL (even causing the neighbors to call the Fire Department, who called out HazMat...), and the problem was corrected with one of the above alternatives...

Just Sayin'...