I drive a 2015 Toyota Tacoma with 6 cylinder engine. Maintenance manual says to use mineral oil but I have used synthetic oil. The service manager says to use mineral oil every 5000 miles. I asked her what is wrong if I used synthetic oil she said I am wasting money to use synthetic oil every 5000 miles. I told her don稚 try to save me money, just answer the question. She repeated the same mineral oil at 5000 miles.
So, is it a money issue, will synthetic harm my engine or is mineral truly the best for my truck?
There are no performance specifications required of a synthetic motor oil over and above those of a refined/mineral motor oil. In other words there are no assurances a synthetic motor oil is superior, or even as good as, a refined motor oil. Only that accepted synthetic manufacturing processes be used. No requirement of what actually gets made.
The only requirement of synthetic is one defined in a court of binding arbitration between the marketing department at Castrol and the marketing department at Mobil. The conclusion was Castrol tried hard enough with hyper-refining that they may sell their oil as "synthetic." That "synthetic" was only a metric of effort not result.
I do not doubt superior motor oil can be manufactured using synthetic processes but I totally doubt the use of synthetic processes guarantees a superior product. I use Mobil-1 because it is a good product with good price at Walmart. The fact it is synthetic is incidental.
You young wippersnappers don't remember The Good Old Days when one selected a motor oil and used religiously for the life of the engine for fear of gaskets and seals leaking. One didn't change from Havoline to Mobil to Quaker State to Pennzoil for fear of leaks. Roads all had big black streak between wheel tracks because everything leaked leaked leaked. When rains came parking lots had oil streaks on the runoff.
Then along came synthetic motor oils and the oil seal thing was blamed on the new motor oils, when all along this was a common problem. The guys making refined motor oils didn't know everything about what they were doing, they just did what their company had always done. And the guys making synthetic motor oil didn't know everything that was expected of a motor oil so they worked on bearing and ring wear.
Then people started studying the oil seal issue and found the rubber/vinyl compounds used absorbed motor oils at different rates. Some brands more than others caused the seals to swell. Swollen seal fit tighter. Tighter wore but still sealed. Then if you came along with a different oil the old leeched out and maybe the new didn't swell as much so the worn seal leaked.
Today the SAE/API specifies how the oil should swell the seal, and seal makers know, and there is no longer a leak issue when changing oils no matter refined or synthetic.
