# About Synthetic Motor Oil... **URL:** \ **Category:** Factual Questions\ **Created:** [February 8, 2015, 10:06pm UTC](https://boards.straightdope.com/t/about-synthetic-motor-oil/712152 "2015-02-08T22:06:33Z")\ **Posts on this page:** 3\ **Page:** 2
**Author:** ![Thudlow\_Boink](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/thudlow_boink/32/320_2.png) [@Thudlow\_Boink](https://boards.straightdope.com/u/Thudlow_Boink)\ **Post date:** [February 9, 2015, 10:16pm UTC](https://boards.straightdope.com/t/about-synthetic-motor-oil/712152/21 "2015-02-09T22:16:55Z")
> [@txtumbleweed](#): > > [According to this GM Bulletin from 2009, expected GM oil consumption is 1qt per 2000 miles.](http://ww2.justanswer.com/uploads/PENTICO/2010-04-03_145717_caddy1.pdf) So if you are on a 10000 mile oil change schedule in a GM car, you can expect to add 4-5 qts between oil changes. If I’m reading that correctly, it says “accepted,” not “expected.” To me, “expected” means average or typical, while “accepted” means within the range of what’s normal and acceptable, but at the upper end of that range. ---
**Author:** ![txtumbleweed](https://avatars.discourse-cdn.com/v4/letter/t/278dde/32.png) [@txtumbleweed](https://boards.straightdope.com/u/txtumbleweed)\ **Post date:** [February 10, 2015, 5:27pm UTC](https://boards.straightdope.com/t/about-synthetic-motor-oil/712152/22 "2015-02-10T17:27:46Z")
> [@Thudlow\_Boink](#): > > If I’m reading that correctly, it says “accepted,” not “expected.” To me, “expected” means average or typical, while “accepted” means within the range of what’s normal and acceptable, but at the upper end of that range. I should have quoted the bulletin as “accepted” not “expected”, there is a difference in connotation. However, it goes to the heart of the argument of documenting what acceptable consumption is. For a GM engine at least, 1qt/2000mi appears to be it. I personally would be worried if my new car was using that much oil, but from GM’s perspective, it isn’t a warranty issue. As for adding oil to a new car engine, I doubt most folks ever really paid too much attention to it in the past. Probably a left over habit from when oil had to be changed every 5000 miles or so. When changing oil every 3000-5000 miles, you might use 1.5-2.5 qts of oil based on GM accepted consumption rate. On an engine that holds 5qts you’d be low, but not dangerously so. If you were getting better than accepted, you would be using even less. If going to a 10000-12000 mile interval as seems to be the case now with the synthetics, you would have used up 5-6 qts of oil with that same engine if you are near that accepted consumption rate. Since you only started with 5qts, you are going to end up doing an engine change along with the oil change. On a tangent, I’ve never understood why there wasn’t a sensor on the dash to tell you when you were a quart low on oil. At least, no car I’ve owned ever had one. I think most didn’t activate until you were already out of oil. ---
**Author:** ![SpeedwayRyan](https://avatars.discourse-cdn.com/v4/letter/s/ce7236/32.png) [@SpeedwayRyan](https://boards.straightdope.com/u/SpeedwayRyan)\ **Post date:** [February 10, 2015, 7:48pm UTC](https://boards.straightdope.com/t/about-synthetic-motor-oil/712152/23 "2015-02-10T19:48:42Z")
> [@txtumbleweed](#): > > On a tangent, I’ve never understood why there wasn’t a sensor on the dash to tell you when you were a quart low on oil. At least, no car I’ve owned ever had one. I think most didn’t activate until you were already out of oil. They’d just need to use an additional sensor. In most cars there’s one measuring oil pressure and only triggering the “idiot light” when oil pressure is dangerously low – which could be due to low oil levels or some other problem. There typically isn’t a sensor or sending unit to measure the actual oil level – it’s certainly possible, but maybe they don’t want you to know how fast your car burns through a quart. 🙂 I know BMW has used oil level senders/lights, as has Mercedes-Benz and Lexus – and likely a lot more…it’s basically a luxury car thing. [Previous page](https://boards.straightdope.com/t/about-synthetic-motor-oil/712152.md?page=1)