Originally Posted by talest
Originally Posted by jongies3
Because they're still under the false impression that thicker protects better when it's hot out. Ambient outside temperature has no effect on oil temp. Your cooling system regulates that!
This was always my impression as well! Now for some more detail. For normal, street-driven regular use cars, I do not think the manufacturer recommended is bad. It should be just fine. A good synthetic will hold up better under high heat, flow better when cold, and most importantly, should not be shearing down in service. Stop and go will heat the oil up faster, there seems to be some debate about the oil temperature vs the coolant temperature, should throw transmission fluid temperature in there too but for now.. Back in the day you probably did need that thicker oil because as it got HOT out and with hard drivin' in the summer, you would not want the protection to break down, I believe this is what it comes down to. Back then, oil was probably mostly garbage dino juice and the thicker grades actually cause a good deal of heat the same as they are supposed to protect from. If anyone ever told you their old Ford truck "took a 20W-50" you could invite them to show you this, where it said that. Maybe it did have some kind of a range that said this could be used in the manual. Then look at the year, and the API service category of said oils. API SF? SG? Hmm. Now look at what was available back then. Tell that to someone in a Deep South summer and something very thick probably got cemented as a go-to oil.
Nowadays, if say an Ecoboost or whatever you got says 5W-20 on the cap, and you run a 5W-20 to not make Ford mad (using Ford as an example here) or even a 0W-20 if that is something they say you can use.... then those are synthetic and mostly synthetic oils anyways, right off the bat and the same as trans fluid that are synthetic anyways - this is also something I have heard said a long time ago, that there is not difference, only in the labeling - and if it does not thin out more than what it already is, and a 20-grade should not be shearing, then you have your protection, and thicker oils can set off all sorts of codes in an engine like Ram or whatever for running something thicker than you are supposed to. We will leave the conversation about
engine feel alone, though I have done many an engine where they come and tell me it revs easier on the thin stuff?
Wanted to give some examples of what I am saying, for those feeling technical.
ISLAC oils shear it's been the nature of the beast for decades and it doesn't matter if it is "synthetic" or not. If using a DEXOS 1 motor oil the preformance is nearly identical across the brands it comes down to what the consumer wants to buy and use.
