Caustic Burno said:
Stocker Steve said:
So some newer engines spec synthetic for longer engine life, or longer change invervals, or tighter clearances, or ???
With uniform molecular structure you can get better lubrication along it takes longer for oxidation and thermal breakdown to occur.
Thermal breakdown starts occurring at 240 degrees in conventional oil.
I had to look this one up synthetic can take up to 450 degrees.
I have proven this to myself by switching from dino to syn oils in my air cooled lawn care equipment. Rather than having to change the oil 2-3 times a season because of dirty oil, I now just change annually, even though measuring around a BS 26 HP Vanguard immediately after a hard workout, other than the exhaust area (around 550F) the hottest spot I could find was 187F with a HF non contact Infrared Thermometer....and it's accurate.
Edit: However, this just hit me. The OHV engine has oil circulating around where the exhaust exits the head (and all) since it lubes the cam and valves. Therefore it is exposed to high temps after all. Maybe not for all that long, but repetitively. So maybe that's the smoking gun that breaks down dino oils.