Hi guys. Please let me clarify the point just made because it can be taken the wrong way. Multi-viscosity oil doesn't "become" thicker when it gets warm. 5W-20 oil acts like cold 5-weight oil when it is cold. It flows better on initial start-up than a higher viscosity oil would. That same oil acts like a hot 20-weight oil when it warms up, so it resists washing off parts too easily. Multi-viscosity oils still get thinner as they heat up. They just retain their designed-in lubricating properties for the intended temperature range. That is done through the use of additives. Those are detergents, dispersants, anti-foaming agents, seal conditioners, and viscosity index improvers. As mentioned, the oil itself doesn't wear out. It's those additives that wear out. The industry standard used to be they would last 3,000 miles. That's why every manufacturer recommended oil changes at that interval. Today the oil formulations had to improve to meet the demands of the newer materials used in engines. That meant it was the additives that had to improve.
You can see this when doing an oil change. Regardless which brand or viscosity oil you're draining out, if it is really hot from a recent run on the highway, it rushes out like water under pressure and splashes all over, including on your hand. If it's cold from sitting in the shop's parking lot for a few hours, it comes out like maple syrup, even if it's straight 5-weight.
Synthetic oil thickens less at cold temperatures than does petroleum-based oil, which is one of its selling features. At minus 30 degrees F. It pours like petroleum oil at 10 degrees F. At minus 60 degrees F. Petroleum oil will be as hard as ice cream. Synthetic oil, I'm told, will still flow, but I don't care to find out for myself.
My truck tells me when to change the oil, but that goes up to 10,000 miles. I become nervous if I let it go much past 5,000 miles. Just because I can doesn't mean I should. The detergents dissolve the sludge and other deposits. Dispersants carry the bad stuff to the oil filter where it is supposed to be trapped. That harmful stuff develops in every gas-powered engine regardless of the type, amount, or condition of those additives. The rate at which the filter plugs up with those contaminants is only related to how fast they're developed, not on how many miles between oil changes. With excessive short-trip city driving, an oil change once a year is way too long an interval. The oil never reaches the temperature the additives were designed to be most effective at. Heat is mostly responsible for wearing out the additives, so with mostly highway miles on long runs, a year is again much too long to wait for an oil change. Everyone you ask will have a different opinion on when the oil should be changed. No two engines see the same type of driving on a regular basis, nor do they get the same maintenance.
Tuesday, March 21st, 2023 AT 5:01 PM