# They want to put synthetic oil in my car. Do I care? **URL:** \ **Category:** Factual Questions\ **Created:** [April 3, 2005, 9:17pm UTC](https://boards.straightdope.com/t/they-want-to-put-synthetic-oil-in-my-car-do-i-care/297571 "2005-04-03T21:17:35Z")\ **Posts on this page:** 20\ **Page:** 1
**Author:** ![Campion](https://avatars.discourse-cdn.com/v4/letter/c/4491bb/32.png) [@Campion](https://boards.straightdope.com/u/Campion)\ **Post date:** [April 3, 2005, 9:17pm UTC](https://boards.straightdope.com/t/they-want-to-put-synthetic-oil-in-my-car-do-i-care/297571/1 "2005-04-03T21:17:35Z")
When I took my car in for an oil change, they told me that the manufacturer now recommends synthetic oil for my car, and did that matter to me. Well, what’s the difference, I ask. A lot of money, they answered. Now, I know that they can take one look at me and know that I won’t understand a scientific answer to the difference between synthetic and natural (??) oil for a car, but they could at least humor me. They didn’t, so I’m asking here. What’s the difference between synthetic and non-synthetic oil used in a car, and (besides the astonishing difference in price), why should I care what type of oil is in my car? ---
**Author:** ![a\_pirahna\_brother](https://avatars.discourse-cdn.com/v4/letter/a/4bbf92/32.png) [@a\_pirahna\_brother](https://boards.straightdope.com/u/a_pirahna_brother)\ **Post date:** [April 3, 2005, 11:11pm UTC](https://boards.straightdope.com/t/they-want-to-put-synthetic-oil-in-my-car-do-i-care/297571/2 "2005-04-03T23:11:25Z")
I guess the first question would be who was changing your oil, the dealer or one of the quick change places? If the answer is the latter, I would take any “advice” or “recommendations” these places give as suspect, especially when it involves your money. > [@](#): > > Now, I know that they can take one look at me and know that I won’t understand a scientific answer to the difference between synthetic and natural (??) oil for a car, but they could at least humor me. They didn’t, so I’m asking here. Don’t feel bad, if it was a quick change place, the person who told you this probably couldn’t have explained either, all they probably knew was dino oil=little money, synthetic oil=mucho money. 🙂 What oil does the owners manual recommend? Second, have you received anything from the manufacturer that modifies the owners manual? If the answer to question one is dino oil and the answer to the second question is no, then I would use what the manual recommends. D. Pirahna ---
**Author:** ![Horatio\_Hellpop](https://avatars.discourse-cdn.com/v4/letter/h/e5b9ba/32.png) [@Horatio\_Hellpop](https://boards.straightdope.com/u/Horatio_Hellpop)\ **Post date:** [April 3, 2005, 11:21pm UTC](https://boards.straightdope.com/t/they-want-to-put-synthetic-oil-in-my-car-do-i-care/297571/3 "2005-04-03T23:21:30Z")
Mobil One is good stuff, esp. for older vehicles. It will make your exhaust smell like Witch Hazel, though. ---
**Author:** ![Campion](https://avatars.discourse-cdn.com/v4/letter/c/4491bb/32.png) [@Campion](https://boards.straightdope.com/u/Campion)\ **Post date:** [April 4, 2005, 12:32am UTC](https://boards.straightdope.com/t/they-want-to-put-synthetic-oil-in-my-car-do-i-care/297571/4 "2005-04-04T00:32:08Z")
The advice came from the dealership; I don’t recall getting anything directly from the manufacturer, but I don’t think the dealership is having me on. My question basically is this: what is the difference between synthetic and non-synthetic oil, and why would the manufacturer recommend, after 4 years of non-synthetic oil, that a vehicle switch to synthetic oil? What differences in performance, if any, should I expect to see? Thanks for any illumination. ---
**Author:** ![sinjin](https://avatars.discourse-cdn.com/v4/letter/s/ebca7d/32.png) [@sinjin](https://boards.straightdope.com/u/sinjin)\ **Post date:** [April 4, 2005, 12:35am UTC](https://boards.straightdope.com/t/they-want-to-put-synthetic-oil-in-my-car-do-i-care/297571/5 "2005-04-04T00:35:26Z")
> [@Krokodil](#): > > Mobil One is good stuff, esp. for older vehicles. It will make your exhaust smell like Witch Hazel, though. ummm, no not, Mobil One is not especially good for older vehicles, it’s mostly irrelevant for older vehicles. Unless your car is designed to use synthetic oils, or you have been using them all the time they are a waste of $$$. Read the manual and do what they suggest. ---
**Author:** ![a\_pirahna\_brother](https://avatars.discourse-cdn.com/v4/letter/a/4bbf92/32.png) [@a\_pirahna\_brother](https://boards.straightdope.com/u/a_pirahna_brother)\ **Post date:** [April 4, 2005, 1:50am UTC](https://boards.straightdope.com/t/they-want-to-put-synthetic-oil-in-my-car-do-i-care/297571/6 "2005-04-04T01:50:20Z")
> [@Campion](#): > > My question basically is this: what is the difference between synthetic and non-synthetic oil, and why would the manufacturer recommend, after 4 years of non-synthetic oil, that a vehicle switch to synthetic oil? What differences in performance, if any, should I expect to see? The only thing I can think of off the top of my head is maybe the manufacturer found out that synthetic oil works better for your car after 4 years, or they should have recommended it to begin with. What kind of car do you have? D. Pirahna ---
**Author:** ![Tuckerfan](https://avatars.discourse-cdn.com/v4/letter/t/eada6e/32.png) [@Tuckerfan](https://boards.straightdope.com/u/Tuckerfan)\ **Post date:** [April 4, 2005, 2:31am UTC](https://boards.straightdope.com/t/they-want-to-put-synthetic-oil-in-my-car-do-i-care/297571/7 "2005-04-04T02:31:34Z")
> [@Campion](#): > > The advice came from the dealership; I don’t recall getting anything directly from the manufacturer, but I don’t think the dealership is having me on. > > My question basically is this: what is the difference between synthetic and non-synthetic oil, and why would the manufacturer recommend, after 4 years of non-synthetic oil, that a vehicle switch to synthetic oil? What differences in performance, if any, should I expect to see? > > Thanks for any illumination. Synthetic oils generally last longer, and many of them claim to lower the amount of friction your engine has to overcome, which should translate into better fuel economy and longer life for your engine. I’ve not seen any studies backing that up, so take it with a grain of salt. If you’ve got a high mileage engine, I would strongly _not_ recommend using a synthetic oil. They work _great_ at flushing the gunk out of your engine, including the gunk that’s helping to keep your engine sealed. If you switch to synthetic oil in such an engine, you might, as I did, suddenly discover in less than 100 miles that your engine is leaking _a lot_ of oil. :eek: ---
**Author:** ![duality72](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/duality72/32/3910_2.png) [@duality72](https://boards.straightdope.com/u/duality72)\ **Post date:** [April 4, 2005, 3:02am UTC](https://boards.straightdope.com/t/they-want-to-put-synthetic-oil-in-my-car-do-i-care/297571/8 "2005-04-04T03:02:08Z")
> [@a pirahna brother](#): > > Second, have you received anything from the manufacturer that modifies the owners manual? It’s so cute you think the manufacturer would actually do that. 🙂 ---
**Author:** ![DrDeth](https://avatars.discourse-cdn.com/v4/letter/d/b487fb/32.png) [@DrDeth](https://boards.straightdope.com/u/DrDeth)\ **Post date:** [April 4, 2005, 3:49am UTC](https://boards.straightdope.com/t/they-want-to-put-synthetic-oil-in-my-car-do-i-care/297571/9 "2005-04-04T03:49:10Z")
If you don’t get regular oil changes as often as you should (generally 4000 or 5000 miles on a newer model car), then yes, the synthetic is worth the $$. So, in other words, if you’re the kind of person that “puts things off” or is “absent minded” or "too busy’ to get those regular oil changes- then, sure, why not. ---
**Author:** ![Enola\_Straight](https://avatars.discourse-cdn.com/v4/letter/e/dec6dc/32.png) [@Enola\_Straight](https://boards.straightdope.com/u/Enola_Straight)\ **Post date:** [April 4, 2005, 4:28am UTC](https://boards.straightdope.com/t/they-want-to-put-synthetic-oil-in-my-car-do-i-care/297571/10 "2005-04-04T04:28:59Z")
Switching may make your engine “addicted” to synthetic. The synthetics often have a tendancy to make oil seals and such swell up, tightening the tolerances around shafts and the like. After the engine re-seats around the new tolerances, a switch back to natural stock oils may make the seals un-swell, causing leaks. ---
**Author:** ![Campion](https://avatars.discourse-cdn.com/v4/letter/c/4491bb/32.png) [@Campion](https://boards.straightdope.com/u/Campion)\ **Post date:** [April 4, 2005, 12:03pm UTC](https://boards.straightdope.com/t/they-want-to-put-synthetic-oil-in-my-car-do-i-care/297571/11 "2005-04-04T12:03:28Z")
Thanks, all. **Tuckerfan** , mine’s not a high mileage engine, but I’ll keep an eagle eye out for oil leaks now. ---
**Author:** ![a\_pirahna\_brother](https://avatars.discourse-cdn.com/v4/letter/a/4bbf92/32.png) [@a\_pirahna\_brother](https://boards.straightdope.com/u/a_pirahna_brother)\ **Post date:** [April 4, 2005, 12:31pm UTC](https://boards.straightdope.com/t/they-want-to-put-synthetic-oil-in-my-car-do-i-care/297571/12 "2005-04-04T12:31:46Z")
> [@duality72](#): > > It’s so cute you think the manufacturer would actually do that. 🙂 I actually recieved an addendum from the manufacturer of my old car, that modified what the owners manual had in it, mmmkay? Just because you haven’t seen it doesn’t mean it doesn’t exist. 🙂 D. Pirahna ---
**Author:** ![kanicbird](https://avatars.discourse-cdn.com/v4/letter/k/5f8ce5/32.png) [@kanicbird](https://boards.straightdope.com/u/kanicbird)\ **Post date:** [April 4, 2005, 1:32pm UTC](https://boards.straightdope.com/t/they-want-to-put-synthetic-oil-in-my-car-do-i-care/297571/13 "2005-04-04T13:32:20Z")
I switched to syn oil in a car w/ 140K miles on it (retired it at 170K miles), I noticed a increase in MPG of about 2, which I always check when I fill up (25\>27mpg). I had no problem with leaking or greater oil consumption. I really didn’t notice anything bad about the switch, even the cost was offset with the increase of MPG, also I increased my oil change interval from 5,000 to 10,000 mi which I would do in 3 months time. I change my own oil, so the cost of the oil change is lower then having it done. ---
**Author:** ![flight](https://avatars.discourse-cdn.com/v4/letter/f/bbce88/32.png) [@flight](https://boards.straightdope.com/u/flight)\ **Post date:** [April 4, 2005, 2:03pm UTC](https://boards.straightdope.com/t/they-want-to-put-synthetic-oil-in-my-car-do-i-care/297571/14 "2005-04-04T14:03:54Z")
> [@Enola Straight](#): > > Switching may make your engine “addicted” to synthetic. > > The synthetics often have a tendancy to make oil seals and such swell up, tightening the tolerances around shafts and the like. After the engine re-seats around the new tolerances, a switch back to natural stock oils may make the seals un-swell, causing leaks. The guys at [Car Talk](http://www.cartalk.com/content/columns/Archive/2002/January/06.html) don’t seem to agree with you. > [@Tom and Ray](#): > > Ray: There is no problem we know of with mixing synthetic and conventional motor oils. I think when synthetics first came out 25 years ago, some manufacturers weren’t sure how well they’d work, whether they’d eat seals and gaskets, or whether they’d mix with conventional oils and create cement. > > Tom: But those concerns were largely dismissed long ago. For some reason – we don’t know why – there are still a few manufacturers that warn against using synthetic oils and some that warn against mixing other synthetics with THEIR synthetic oil. We’ve never seen a problem in the shop related to this stuff, but you should check your owner’s manual for a prohibition, just to be safe. > > Ray: But the vast majority of manufacturers now treat synthetics just like a premium, high-priced motor oil that can be mixed and matched with other oils at the whim of the customer – that’s you, Bill. So as long as your owner’s manual doesn’t specifically forbid it, do whatever you want. ---
**Author:** ![ralph124c](https://avatars.discourse-cdn.com/v4/letter/r/8797f3/32.png) [@ralph124c](https://boards.straightdope.com/u/ralph124c)\ **Post date:** [April 4, 2005, 2:14pm UTC](https://boards.straightdope.com/t/they-want-to-put-synthetic-oil-in-my-car-do-i-care/297571/15 "2005-04-04T14:14:20Z")
What’s the story with these 10,000 mile oil-change intervals? As far as I know, doing this would absolutely VOID a new car warranty? Synthetic has one big advantage-it does not break down readily until high temperature conditions. So, for a regular passenger car, using synthetic is mostly a waste of money. ---
**Author:** ![kanicbird](https://avatars.discourse-cdn.com/v4/letter/k/5f8ce5/32.png) [@kanicbird](https://boards.straightdope.com/u/kanicbird)\ **Post date:** [April 4, 2005, 2:32pm UTC](https://boards.straightdope.com/t/they-want-to-put-synthetic-oil-in-my-car-do-i-care/297571/16 "2005-04-04T14:32:00Z")
> [@](#): > > What’s the story with these 10,000 mile oil-change intervals? It’s mainly a convience factor for me (when the odometer goes over the next 10K it’s time again), my car was way out of warranty, and it was getting rediculus keeping up with the 5K interval due to my high amount of driving. I qualify for the 7,500 mile oil change according to the driving I do, but didn’t want to push it to 10K. Switching to syn oil gave me the piece of mind to push it to 10k. > [@](#): > > Synthetic has one big advantage-it does not break down readily until high temperature conditions. So, for a regular passenger car, using synthetic is mostly a waste of money. A regular passenger car has a cooler engine in it? Perhaps they are only driven when the projected high won’t go over 50F? This doesn’t really make any sense unless you are compainig it to a military vehical. And as I pointed out the boost in MPG offsets the cost of syn oil (for me, YMMV) ---
**Author:** ![badmana](https://avatars.discourse-cdn.com/v4/letter/b/977dab/32.png) [@badmana](https://boards.straightdope.com/u/badmana)\ **Post date:** [April 4, 2005, 3:19pm UTC](https://boards.straightdope.com/t/they-want-to-put-synthetic-oil-in-my-car-do-i-care/297571/17 "2005-04-04T15:19:16Z")
> [@ralph124c](#): > > What’s the story with these 10,000 mile oil-change intervals? As far as I know, doing this would absolutely VOID a new car warranty? Synthetic has one big advantage-it does not break down readily until high temperature conditions. So, for a regular passenger car, using synthetic is mostly a waste of money. I think you’re talking about by-pass filters. I know Amsoil sells regular (synthetic) oil with a “10,000 mile” change interval but it’s probably because of their filter. A by-pass filter is one that’s 10X more “filtery” than a regular one. Filters down to 5 microns IIRC which is considerably better than your regular oil filter. Big rigs generally use them and you can have one installed for ~$200. I don’t know if it will mess with your warrenty. Of course at the same time I’ve never heard of a engine dying from dirty oil (no oil is different). I think oil type is over rated. Regular or Synthetic is just fine as long as it’s changed on time. Unless you track your car or drive hard in the desert, you shouldn’t worry about synthetic/regular oils as long as you’re using the right oil weight (5W30, 10W30 etc). ---
**Author:** ![Balthisar](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/balthisar/32/2825_2.png) [@Balthisar](https://boards.straightdope.com/u/Balthisar)\ **Post date:** [April 4, 2005, 3:48pm UTC](https://boards.straightdope.com/t/they-want-to-put-synthetic-oil-in-my-car-do-i-care/297571/18 "2005-04-04T15:48:35Z")
I’d stop going to that dealer, unless they had some official manufacturer documentation that specifically backs up their claim, otherwise _they’re just frigg’ lying to you_. Yes, _ **LYING** _. And you shouldn’t hesitate to tell them that. The wholesale price of synthetic oil is not too much different that natural oil, but yet the markup is a _definite_ advantage to them – kind of like the sellup on premium gas for cars that only need regular. Check for this seal on oil: [example](http://www.dippy.org/svcman/image/0004.jpg). This oil is satisfactory for _all_ cars that use this grade. There’s not a company in the world\* that makes a car that requires anything beyond the SAE logo. \*okay, maybe there are some exotic cars that do; let’s make that “mass market.” Also some specialized engines _maybe_ want synthetic oil, but everyone I’ve ever known with a supercharger or turbo used regular oil (warning: small sample size). ---
**Author:** ![meanoldman](https://avatars.discourse-cdn.com/v4/letter/m/7ab992/32.png) [@meanoldman](https://boards.straightdope.com/u/meanoldman)\ **Post date:** [April 4, 2005, 4:12pm UTC](https://boards.straightdope.com/t/they-want-to-put-synthetic-oil-in-my-car-do-i-care/297571/19 "2005-04-04T16:12:20Z")
IANAMechanic. I have a '98 Dodge Van and a '99 Ford F150. Mix and match ‘regular’ oil and synthetic in both vehicles, depending upon whim and available cash. I have zero problem with any vehicle using a lot of oil. As at least one previous poster mentioned, synthetic oil is supposedly better at guarding against thermal breakdown, and I understand it “stays in grade” longer at the low end too. (that is, it lasts longer at both the 5 or 10 weight _and_ at the 30 or 40 weight). Once the vehicle is out of warranty, I judge how often I need an oil change not by the calendar or by number of miles on odometer… but by looking at the oil. If it’s as black as midnight on a moon-less night… time for a change. Otherwise, its good to go. I always thought it was the amount of particulates suspended in the oil that will do the long term damage to an engine and its parts. ---
**Author:** ![brownie55](https://avatars.discourse-cdn.com/v4/letter/b/f14d63/32.png) [@brownie55](https://boards.straightdope.com/u/brownie55)\ **Post date:** [April 4, 2005, 4:48pm UTC](https://boards.straightdope.com/t/they-want-to-put-synthetic-oil-in-my-car-do-i-care/297571/20 "2005-04-04T16:48:15Z")
> [@Balthisar](#): > > okay, maybe there are some exotic cars that do; let’s make that “mass market.” Also some specialized engines _maybe_ want synthetic oil, but everyone I’ve ever known with a supercharger or turbo used regular oil (warning: small sample size). My turbocharged WRX gets nothing but Mobil 1, but I beat the snot out of it. For normal driving the regular always worked fine for me. [Next page](https://boards.straightdope.com/t/they-want-to-put-synthetic-oil-in-my-car-do-i-care/297571.md?page=2)