I always thought that Mazda recommending against synthetic oil in rotary applications was weird as they claimed it wouldn't burn as clean in the combustion chamber vs a conventional oil. Wouldn't a more refined oil like synthetic burn cleaner if the molecules were more even and more refined?
Urban Legend from decades ago ... synthetic oil was "too slick" for engines
- Thread starter cammyfive79
- Start date
Kestas
Staff member
The "skating" you talk about is called "skidding" in the bearing world. This is a phenomenon that occurs during high rotational acceleration such as with air tools. The fix is to design the bearing with heavier preload.
Yes, and sythetic gasoline. It was actually made from coal tar distillate. Benzene anyone?
Was there an "online" then?
Synthetic resists burning to a considerably higher temperature than conventional. Even in a piston engine a fair amount of oil gets past the rings. Synthetic not burning actually means must of it stays on the cylinder wall and makes its way back to the crankcase.
Back in the’80s my commute car was an 83 Civic FE (Fuel economy). I tried a number of oils and chose based on what used the least fuel. The winner was Chevron synthetic 5W/30. Sadly it was only available for a few years. Mobil 1 was almost as good, so I used it after the Chevron became unobtainable.
At the same time Mobil had aviation synthetic oil available for a short while. It didn’t do a good job dispersing lead and the rings would load up so it was recalled. But my plane got about 5% better fuel economy when I used it. Likely because it did a better job of ring sealing…..At least until lead accumulation became a problem.
How does this keep getting repeated?!?!
I WAS THERE. In the 80s, switching to Mobil 1, 10w-30 almost instantly wiped out main seals and dumped oil everywhere. I always knew this going in, and always just replaced the main seals when oil started leaking all over the place, after a hundred miles or so. It was the price I expected to pay, to run those older design motors out past 200,000 miles, which was far less commonplace then. Being a lot younger, I didn't mind getting greasy, getting under the car, and replacing seals. Seals were a lot easier to get to in those days too, in fact a lot of cars were designed so the main seals could be replaced in an hour.
But Mobil1 made engines leak, period. Anyone saying anything contrary just goes to show what a heaping pile the internet has become. Dead internet is real, AOL starting endless summer was just the beginning.
Definitely. I was part of a few car forums starting around that time. I spent many nights/weekends in our university “computer lab” on automotive and stereo/home theater forums. BITOG is one of the last true online forums I’m involved with daily as many of them have went the way of the dinosaurs.
My first new car was a 1978 VW Rabbit. Loved it. Quick, took corners like it was on rails, fuel injected, good MPG and was a far sight better than the Pinto/Gremlin/Vega offerings of the era. I eagerly tried Mobil 1 very early on, one-quart metal cans, but my engine couldn't hold oil pressure. The low oil pressure dummy light would constantly flicker at idle, and the idle was set at the right RPM. So perhaps it was "too slick." 
Carlostrece
$100 Site Donor 2025
Synthetic oils are slipperier than conventional oils. That's great for lubrication and wear reduction, but tends to leak more past old seals, gaskets, and worn rings.
Syn oil being slipperier makes it easier for it to slip past old seals, gaskets, & worn rings in worn cylinders. Thus syn is more likely to leak, burn, or use/lose oil, especially in an old car that's high miles. Even moreso if that old HM car had used conventional oil its entire life because it'd have more wear.
Back in the day, the ideal time to switch to syn was around 30K miles, but 50K was pretty good too. IME 75K miles was still safe to switch to syn if the car had been well maintained.
The part the service guy said about sportcars probably meant only cars driven very hard needed synthetic. I agree that was true back then. However, he should have also included vehicles that haul or tow heavy loads.
I also agree with what was said in post 48 about oil pressure. I experienced same when I switched a 99 Jeep 4L with 30K miles from 10w30 conv to 10w30 Mobil One. Low oil pressure at idle. I resolved that by switching to Mobil One 5w40. Then ideal oil pressure.
If/when I switch a HM car from conv to syn, I choose a syn that's thick for its grade, or go up one grade. Then oil pressure still good and hopefully no leaks or oil burning.
I agree with what the dealership service guy told you. He didn't want to risk starting/causing an oil leak, low oil pressure at idle, or burning oil. If any of those problems began after he changed your oil, you'd come back and complain, which would make it his problem.
In current times, a lot of modern engines are less robust, less durable and need syn oil just to survive normal driving. i.e. - A lot of modern engines are whiny snowflakes. The good thing is that the modern engines that need syn have it in them their entire lives. So there are no changeover concerns.
The engine tech has changed for better and worse. Mostly worse after 2005, IMO. Oil tech has improved, but that is somewhat cancelled by some modern engines being designed more fragile than used to be.
Syn oil being slipperier makes it easier for it to slip past old seals, gaskets, & worn rings in worn cylinders. Thus syn is more likely to leak, burn, or use/lose oil, especially in an old car that's high miles. Even moreso if that old HM car had used conventional oil its entire life because it'd have more wear.
Back in the day, the ideal time to switch to syn was around 30K miles, but 50K was pretty good too. IME 75K miles was still safe to switch to syn if the car had been well maintained.
The part the service guy said about sportcars probably meant only cars driven very hard needed synthetic. I agree that was true back then. However, he should have also included vehicles that haul or tow heavy loads.
I also agree with what was said in post 48 about oil pressure. I experienced same when I switched a 99 Jeep 4L with 30K miles from 10w30 conv to 10w30 Mobil One. Low oil pressure at idle. I resolved that by switching to Mobil One 5w40. Then ideal oil pressure.
If/when I switch a HM car from conv to syn, I choose a syn that's thick for its grade, or go up one grade. Then oil pressure still good and hopefully no leaks or oil burning.
I agree with what the dealership service guy told you. He didn't want to risk starting/causing an oil leak, low oil pressure at idle, or burning oil. If any of those problems began after he changed your oil, you'd come back and complain, which would make it his problem.
In current times, a lot of modern engines are less robust, less durable and need syn oil just to survive normal driving. i.e. - A lot of modern engines are whiny snowflakes. The good thing is that the modern engines that need syn have it in them their entire lives. So there are no changeover concerns.
The engine tech has changed for better and worse. Mostly worse after 2005, IMO. Oil tech has improved, but that is somewhat cancelled by some modern engines being designed more fragile than used to be.
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I am calm.
But, I am not gullible.
And if the legend was “online” then, we are not talking about the 1980s/1990s, are we? Because nobody was “online” most of those years.
I wonder how slipperiness is measured, and what makes a synthetic more slippery? Today's Group III synthetics are the same chemical structure as "conventional" oil, whatever that means in the world of API SP.
Also if it is a Group IV synthetic, PAO actually has a higher coefficient of friction. So this who thing about synthetics being more slippery than a conventional is just not true.
I was there too! But actually a little before you, I used Mobil 1 in both my 1974 and 1979 car and guess what? No wiped out main seals and didn't dump oil everywhere. How can that be?
Plus this was the original Mobil 1 5W-20! Wow! How did I ever survive? Am I part of the heaping pile?
Don’t forget, “slipperier” means that it slips past main seals, too…
Yeah those Saab 900's would go hundreds of thousands of miles.
When Mobil 1 came out, I put it in my slant 6 Duster. It seemed to go thru it like water. Couldn't justify the cost of adding oil all the time. Switched back to regular oil and no oil usage.
Which is a bit different than it "almost instantly wiped out main seals" and "dumped oil everywhere".
I was there in the 90's with my 1978 Camaro with a 1979 305 that someone had replaced the stock V6 with before I got it. That engine was bone stock except for the intake manifold, cam and carb.
I put every synthetic oil I could find in there because....horsepower!
The only thing that ever leaked was the valve covers because I had crushed the cheap cork gaskets.
I put every synthetic oil I could find in there because....horsepower!
The only thing that ever leaked was the valve covers because I had crushed the cheap cork gaskets.
If this urban legend started in the 80s/90s with vehicles of that era then it certainly would pertain to the 1989 model I bought in 1998 when my online life began on car forums. Yes, in my experience, it was often said (in online forums) that I shouldn't use a full synthetic on an older car; the service advisor I dealt with back then parroted this view as well. I didn't claim it was correct, I started the topic curious as to why people generally thought this or if there was a kernel of truth to it that was falsely extrapolated to "don't use a synthetic on an old car because it's too slick" etc.
Carlostrece
$100 Site Donor 2025
You can have your opinion. I have mine. I know several certified mechanics who say exactly what I said. Possibly you may know others who think differently.
The dealership wasn't going to risk a potential problem that might come back to them. The dealership played it safe. If the customer wanted to experiment by personally changing his oil from conv to syn in a high mileage car, that would be fine because it would be his risk. Switching that old HM car from conv to syn might have worked out fine, or might not. The dealership didn't want to risk it.
I've switched multiple HM cars from conv to syn.
Several old HM cars that I switched started leaking oil, and/or burning oil, and/or had lower oil pressure at idle. Switching those cars back to conv resolved those issues.
A few of the old HM cars I that switched from conv to syn had no problems.
If a person wants to switch an old HM car from conv to syn, then I suggest a HM syn oil to give the best chance for not leaking. My preferred HM syn for that is Quaker State High Mileage Full Syn because it's thicker than other HM syn oils.
My other preference is a HM blend oil such as Maxlife Blend or Quaker State HM (blend). Of the two, QS HM is thicker than Maxlife Blend, but I have had good results with Maxlife Blend. Maxlife Syn leaked like a sieve in that same car.
The thickest HM (blend) that I know of is Pennzoil HM (blend). But I don't need that thick to prevent my car from leaks, and it might be a bit thicker at cold start than I'd want.
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OVERKILL
$100 Site Donor 2021
Mechanics generally know little to nothing about engine oil, just like the guys swapping parts at power plants generally don't know much about the lubricants used in the turbines, it's Engineers that get into that data and analyze it.
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