Where did this misinformation start?

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May 11, 2004
St. Paul, MN
I have a couple older guys in the shop I work at that swear that synthetic is "A thinner oil".


Tech 1: "Maybe we should put synthetic oil in this car. It might burn less(oil)."

Old Timer Tech 2: "Nah. It would probably burn more. That synthetic is pretty thin."

I have heard this from a couple different people. I try to explain that viscosity is viscosity no matter what type of oil. I was thinking that maybe syn IS thinner when it is -20 outside but that is exactly when you need it.
you are correct.
syn is made in a lot of grades thin to thick the old timers are not remembering right or there experience is with only one oil a long time ago and they are baseing there observation on this.
There's a mechanicnear here, who advise their oil burning customers to "fill it with Mobil 1 and sell it".

Apparently, M1 cannot burn, so the oil leaves the exhaust without smoke.

Some workmates have followed his advice and seen a severe reduction in smoke "as the synthetic replaces the old oil" in the leak prone areas...therefore it must be true.
The idea that the oil is thin comes from the fact that in the early days of synthetic automotive oils the oils were prone to weeping and leakage caused by incompatibility with sealing materials of the time. To the casual observer it seemed to make sense that the oil leaked past the seals because it was thinner.

Keep in mind that nearly nobody has any idea what centistokes or centipoise are.
Pouring M1 10W-30 vs. Castrol 20W-30. One is synthetic and it is "thinner" because it pours fast. No other science need apply, saw it with their own two eyes.

First perceptions are very convincing and often very stubborn. I can't say they are usually wrong - but many are.

Enough said.
it used to be "common knowledge" that synthetic oil molicules were "smaller" than dino oil, therefore making it "thinner". that is where the old wive's tale comes from.
The Mobil1 TV ads showed the frozen dino oil thick as molasses, and the smoking dino oil in the frying pan. Seeing is believing.
I may be mistaken but I believe some of the M1 print ads from the seventies actually stated something to the effect of "thinner start up viscocity compared to conventional oil, meaning reduced cold cranking wear."
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