I had Midas put synth in my 2006 RAV4 on a whim a couple of times around 2010 or so, I think they used Valvoline but I'm not sure. They told me that I could never go back to conventional after that, but even then I smelled a strong whiff of BeeEss on that one. I know that a statement like this opens me up to ridicule, but the RAV4 felt "slippery" to me after the first synth change...it's hard to explain exactly what I mean, but I have seen other people online use the same term for the sensation and it was the term that came to mind when I first started driving the car. It sounds insane and I can't explain it, but I went into it thinking that the oil might just last longer and was shocked to find myself thinking the car had a different feel...I almost wanted to have the stuff drained out at first.
My first DIY change, which was also my first with synth, was in 2014 with M1 5W30 in my '14 FXT.
Around 1994 ish. Castrol Syntec 5w-50 black bottle with the hexagonal cap.
It caused the front main seal to fail in my 1980 Lebaron 318 V8. Stopped using it after 2 or 3 changes. Went back to Castrol GTX 10w-40.
The 5w-50 did quiet the engine and it ran great.
Resumed using synthetic (Mobil 1 10w-30 in my 1997 Ram 1500 5.9 gas) in 1997.
About 2004 when I discovered the Product Rebates, Sales & Promotions section. I bought up the shelf from AutoZone's variety of synthetic oils. IIRC, I scarfed up about 30 qts of oils(Mobil 1, Castrol SynTec, Havoline Syn etc.) all SL/GF-3, for $.75-$1 qt.
Then I also grabbed the remaining .50 cent dino oils. This was my first time getting into scoping out discontinued oils when new certification were changing from SL to SM.
Since then, this is how I buy my oils now. Recently, I crabbed the discontinued Quaker State dino & synthetic from Advance Auto Parts(all SN/GF-5). Most for $1 or less/qt. Some 5qt jugs of QSUD too.
Mobil had already released their Mobil 1, but I just couldn't get there using a 20W-20 (the only weight available then, as I recall).
I found they had a 10w-30 or so called Delvac 1, a synthetic in the Mobil 1 family, and went with that. It was meant for OTR trucks.
I actually gained 1 mpg, consistently, in my old SAAB 99 I was using on the road then. It would turn about 3500 rpm at 70 or so, and I wasn't comfortable with a 20 weight for it.
Wow.......brings back some memories!
I started using Synthetic Oil in 1985..........it was on my brand new 1984 Honda Prelude.
It was "Mobil-One"
If I remember correctly, at that time there was no Viscosity listed on the Cardboard with Metal top can. It was just "Synthetic".
About 1981. Mobil 1. I was using Esso Uniflo at the time. I read Mobil 1 came out in 1974. A professor in the department of mechanical engineering of the local university said they were extremely impressed by it. He said to me "if you keep your air filter clean and use synthetic oil, your engine might never wear out." That was around 1976.