# Is all motor oil created equal? **URL:** \ **Category:** Factual Questions\ **Created:** [September 28, 2017, 2:03am UTC](https://boards.straightdope.com/t/is-all-motor-oil-created-equal/797479 "2017-09-28T02:03:23Z")\ **Posts on this page:** 9\ **Page:** 2
**Author:** ![icbm](https://avatars.discourse-cdn.com/v4/letter/i/2acd7d/32.png) [@icbm](https://boards.straightdope.com/u/icbm)\ **Post date:** [September 28, 2017, 9:10pm UTC](https://boards.straightdope.com/t/is-all-motor-oil-created-equal/797479/21 "2017-09-28T21:10:42Z")
> [@Leaffan](#): > > I recall decades ago either reading or watching something on a study done in New York City taxis. I think that was Consumer Reports. Let’s see if Google agrees… Wow, 1996. Good memory, Leaffan. [http://www.xs11.com/xs11-info/xs11-info/articles/51-consumer-reportstruth-motor-oils-july-1996.html](http://www.xs11.com/xs11-info/xs11-info/articles/51-consumer-reportstruth-motor-oils-july-1996.html) ---
**Author:** ![Leaffan](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/leaffan/32/299_2.png) [@Leaffan](https://boards.straightdope.com/u/Leaffan)\ **Post date:** [September 28, 2017, 9:24pm UTC](https://boards.straightdope.com/t/is-all-motor-oil-created-equal/797479/22 "2017-09-28T21:24:20Z")
> [@icbm](#): > > I think that was Consumer Reports. Let’s see if Google agrees… > > Wow, 1996. Good memory, Leaffan. > > [http://www.xs11.com/xs11-info/xs11-info/articles/51-consumer-reportstruth-motor-oils-july-1996.html](http://www.xs11.com/xs11-info/xs11-info/articles/51-consumer-reportstruth-motor-oils-july-1996.html) Yes. That’s the study I recall reading. Thank you. Bottom line, no difference in performance if you follow the viscosity and change interval with an approved oil. Even synthetics aren’t any better, under normal driving conditions. ---
**Author:** ![Melbourne](https://avatars.discourse-cdn.com/v4/letter/m/b5e925/32.png) [@Melbourne](https://boards.straightdope.com/u/Melbourne)\ **Post date:** [September 28, 2017, 11:00pm UTC](https://boards.straightdope.com/t/is-all-motor-oil-created-equal/797479/23 "2017-09-28T23:00:49Z")
> [@Lightray](#): > > Next, oil weight: the engine manufacturer designs the engine tolerances with a very narrow range of viscosity for optimum performance. The recommended oil weight is the result of them trying to keep you in that optimum range. It has very little to do with the performance additives in the motor oil (other than some solubility stuff). You should use the recommended motor oil weight for your engine for best performance. A ‘20’ weight oil has a viscosity of 20, right? But a 10-30 oil has a viscosity of 10 at low temperatures, and a viscosity of 30 at high temperatures? So if you are starting your engine at low temperatures, your owners manual will recommend using a 5-30 oil: if you are starting at high temperatures, it will recommend a cheaper 10-30 oil. Apart from that, if your engine is running in the recommended temperature range, using a wide range oil (10-50) won’t have any effect, but will not make performance ‘worse’ in any way, right? ---
**Author:** ![jz78817](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/jz78817/32/1028_2.png) [@jz78817](https://boards.straightdope.com/u/jz78817)\ **Post date:** [September 28, 2017, 11:21pm UTC](https://boards.straightdope.com/t/is-all-motor-oil-created-equal/797479/24 "2017-09-28T23:21:52Z")
> [@Melbourne](#): > > But a 10-30 oil has a viscosity of 10 at low temperatures, and a viscosity of 30 at high temperatures? Yes, -25 and +100C IIRC. > [@](#): > > Apart from that, if your engine is running in the recommended temperature range, using a wide range oil (10-50) won’t have any effect, but will not make performance ‘worse’ in any way, right? Since the second number is the viscosity index at normal engine operating temperature, you do not want to use an oil with a higher “hot” viscosity index than recommended. ---
**Author:** ![Lightray](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/lightray/32/391_2.png) [@Lightray](https://boards.straightdope.com/u/Lightray)\ **Post date:** [September 28, 2017, 11:31pm UTC](https://boards.straightdope.com/t/is-all-motor-oil-created-equal/797479/25 "2017-09-28T23:31:32Z")
As I said, the motor oil weight doesn’t have much to do with the performance additives, so I don’t have much data on the effects (I’m not a formulator; I make the additives that go _into_ the formulated blend). But. As far as I know, the car companies choose the recommended oil based on the expected _operating_ temperature, and they do believe that engine performance will be worse if you’re not at that expected operating viscosiity. It mostly shows up in the legal claims they make for engine performance and efficiency; they disclaim that you would receive the same results if you don’t use the recommended oil. The engine _start_ temperature is accounted for in the additive package – by the addition of viscosity index improvers (which change the slope of the temperature-viscosity curve, basically). So if the manufacturer is recommending a different oil for use in low temperatures, you’re essentially getting more VII. I would assume the manufacturer would recommend something like a 10w-30 for normal operation, or a 5w-30 for cold weather operation. I expect they would suggest that using a 5w-30 instead of 10w-30 if you’re not in cold weather would still be preferable to instead using a 10w-50, though. ---
**Author:** ![Blakeyrat](https://avatars.discourse-cdn.com/v4/letter/b/ecd19e/32.png) [@Blakeyrat](https://boards.straightdope.com/u/Blakeyrat)\ **Post date:** [September 29, 2017, 12:10am UTC](https://boards.straightdope.com/t/is-all-motor-oil-created-equal/797479/26 "2017-09-29T00:10:26Z")
> [@thelurkinghorror](#): > > Conventional oil should be changed every 5000 miles or more, check your car’s manual. 3000 miles has not been true for at least 2 decades, but is a common myth still. It’s good to do if you really hate money. Synthetic can be changed less often. > > My car is from 1999 and recommends 5000. My 2014 Ford Fusion specifies synthetic and goes an average of 11,000 miles between changes. Just as a data point. ---
**Author:** ![rbroome](https://avatars.discourse-cdn.com/v4/letter/r/838e76/32.png) [@rbroome](https://boards.straightdope.com/u/rbroome)\ **Post date:** [September 29, 2017, 12:14am UTC](https://boards.straightdope.com/t/is-all-motor-oil-created-equal/797479/27 "2017-09-29T00:14:47Z")
> [@Lightray](#): > > As I said, the motor oil weight doesn’t have much to do with the performance additives, so I don’t have much data on the effects (I’m not a formulator; I make the additives that go _into_ the formulated blend). > > But. As far as I know, the car companies choose the recommended oil based on the expected _operating_ temperature, and they do believe that engine performance will be worse if you’re not at that expected operating viscosiity. It mostly shows up in the legal claims they make for engine performance and efficiency; they disclaim that you would receive the same results if you don’t use the recommended oil. > > The engine _start_ temperature is accounted for in the additive package – by the addition of viscosity index improvers (which change the slope of the temperature-viscosity curve, basically). So if the manufacturer is recommending a different oil for use in low temperatures, you’re essentially getting more VII. I would assume the manufacturer would recommend something like a 10w-30 for normal operation, or a 5w-30 for cold weather operation. I expect they would suggest that using a 5w-30 instead of 10w-30 if you’re not in cold weather would still be preferable to instead using a 10w-50, though. Thanks!. I echo LSLGuy’s comments. The Dope always seem to have the experience. 🙂 ---
**Author:** ![Crafter\_Man](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/crafter_man/32/458_2.png) [@Crafter\_Man](https://boards.straightdope.com/u/Crafter_Man)\ **Post date:** [September 29, 2017, 1:41am UTC](https://boards.straightdope.com/t/is-all-motor-oil-created-equal/797479/28 "2017-09-29T01:41:39Z")
> [@Melbourne](#): > > But a 10-30 oil has a viscosity of 10 at low temperatures, and a viscosity of 30 at high temperatures? “10” and “30” are not viscosity numbers. They refer to the “weight” of an oil. All motor oil - even blended oil - is thicker at cold temperatures and thinner and high temperatures. Let’s say you use 10W-30 weight oil in your car. This means, a) At -25 °C, the oil has the same viscosity as straight 10-weight oil at -25 °C. b) At 100 °C, the oil has the same viscosity as straight 30-weight oil at 100 °C. So as can be seen, at 100 °C, 10W-30 oil is thinner (i.e. has less viscosity) than at -25 °C. But the slope of the curve is less than if you were to use straight 10-weight oil or straight 30-weight oil. ---
**Author:** ![Isilder](https://avatars.discourse-cdn.com/v4/letter/i/cc9497/32.png) [@Isilder](https://boards.straightdope.com/u/Isilder)\ **Post date:** [September 29, 2017, 3:02am UTC](https://boards.straightdope.com/t/is-all-motor-oil-created-equal/797479/29 "2017-09-29T03:02:39Z")
> [@t-bonham@scc.net](#): > > Synthetic oil vs. natural petroleum oil is said to make a difference for some uses. Personally, I’ve never noticed any difference in use. But anyway, synthetic isn’t costing that much more, so don’t worry, so you can easily get a modern standard of synthetic which doesn’t cost much more than a sorta modern standard of mineral. (like SF mineral vs SJ synthetic) … The newer standards are cleaner and keep the engine cleaner… less sludge means less chance of an expensive premature failure due to oil starvation somewhere. [Previous page](https://boards.straightdope.com/t/is-all-motor-oil-created-equal/797479.md?page=1)