Conventional vs. Synthetic Oil

Factual Questions
1

I’m bringing my 2019 Hyundai Elantra in for its first oil change.

The oil weight recommended is 5W-20; it says this right on the cap on the engine.

I’m not a car person, so called a few dealerships to find out what type of oil I should use.

The first dealership said conventional.
The second dealership said synthetic.
The third dealership said synthetic blend.

The owner’s manual does not have a recommendation (apart from the weight).

I had previously taken the car in to a shop to have the oil changed and we decided it didn’t need it yet (the car was at 6 months, but only about 1,500 miles). They weren’t sure what oil to use and they said they called a dealership while I was there and the dealership said synthetic.

I know synthetic is more expensive, but this shop, if they were trying to take advantage of me, could’ve just done the oil change then instead of telling me it wasn’t necessary, so I don’t have a real reason to disbelieve that they called a dealership and were told synthetic.

If it makes a difference, I don’t drive much, obviously - about 200-250 miles per month. 95% of my driving is city driving - stop-and-go, short trips. I live in Seattle, and the car sits in a garage when not being used.

So what’s the deal? Does it make a difference? No damage can be done to the car by putting in a conventional vs synthetic, right?

I can’t seem to get the straight dope from dealerships, so thought I’d try here.

2

This should probably be moved to IMHO, because it’s likely the answer will boil down to opinions (unless the manufacturer specifically says to run one vs the other).

Check your owner’s manual.

It’s possible/ likely the manufacturer just wants good oil in your car, changed regularly. If so, and if you only accrue miles at the rate you have thus far, my opinion would be to change the oil once per year, with conventional oil and a factory filter and call it good

My opinion is based on my real life application to my own vehicles.

My 2007 car, which I drive only rarely, sees as many miles as your car does. I change it once a year with good conventional oil, still looks fine when I do, I’ve had no problems.

My 2003 pickup (5.3 GM gasoline engine) I drive all the time, it gets full synthetic. It’s got 325K miles on it and doesn’t burn any that I can tell (does leak a little). I go 10K on changes and do a new filter every 5K.

My reasoning is saving money on the car, with no sacrifice in quality of maintenance, and taking advantage of extended oil change intervals on the truck, also therefore saving money, by using a superior oil.

*Typically, you never want to run synthetic until the piston rings have seated (let’s say anything over 5K miles you’re probably safe).

*Someone will likely chime in and say that synthetic works well for low mileage applications too - it’s a better oil in general, of course it does.

*Someone will likely chime in and say I could get longer intervals out of my trucks oil - they’d be correct again, I just chose 10K because it works for me and has got me this far.

*For more info and opinions on lubricants than you’ll likely ever care to explore, go to https://www.bobistheoilguy.com/ and read till your head explodes.

3

Your driving cycle is severe, and you are looking at a annual oil change intervals with your mileage. Your most likely going to accumulate hydrocarbons and water in the oil and not get it hot enough to burn it off. That speaks synthetic to me, you want the better quality to preserve the oil integrity once it starts building up contamination, including making sure you check the oil level throughout the year (including checking for too high an oil level). The other option I would go for is conventional at 6 month intervals.

4

To help me follow the discussion, could you explain the difference between the two types of oil? I’ve wondered that from time to time but never remembered to ask here.

5

I’ll try an analogy :

Say you want 100 balls in a box such that the total weight is 500 lbs and the average weight, hence, of individual balls is about 5 lbs.

Conventional Oils : you have barrels of 20 lb balls, 10 lb balls, 2 lb balls and 1/2 lb balls. You mix these balls up such that you exactly have 100 balls and the total weight is 500 lbs. (and average weight of 5 lbs). You are incentivized to use the 20 lb and 1/2 lb balls more since these balls cost less. However over time, the 20 lb ball gunks up (oxidizes) and the 1/2 lb ball vaporizes from the oil

Synthetic oils : You have a way of breaking the big balls and/or joining the small balls to make medium sized balls (in chemical engineering / chemistry jargon this is called synthetic balls ) . So now you have barrels of balls : 4 lb balls, 5 lb balls and 6 lb balls. You again pick different balls to make up the 100 balls with the average weight of 5 lb and 100 of them total. But in this instance you don’t have the big deviations from average that conventional oil had.

6

That’s what I do with my new Cherokee. I only drive around 6,000 miles a year (pretty much city driving). So I have the oil changed twice a year [late spring/early summer and right before the winter]

7

An average of 8 to 10 miles per trip, city driving, in a late model fuel injected car should give the engine time to warm up sufficiently I’d think. New cars come up to temperature more quickly by design, and the fuel systems better manage the fuel that’s injected to avoid excess. I think your concern is a valid one to consider, I just think it’s less likey nowadays as compared to an older vehicle with a carburetor.

My thoughts are based on my having experienced exactly what you’re referring to on a former older truck with a carb, and not experiencing it on my 2007 vehicle, both being driven similar miles and styles.

When I check the oil before I change it, I feel the oil as well. On my 2007 car, it still feels nice and slippery, it’s also not overfull. The old trucks oil would be a little overful and when you rubbed it between your fingers you could tell it wasn’t capable of doing its job as well as oil that wasn’t a little fuel fouled would.

In general I say the odds of a lubrication related issue on a car that would only have 45K miles at the 15 year mark would be near nonexistant, no matter which oil he decides to use.

*To the OP, the way to determine this for sure, and not base anything off people’s opinions and personal experiences, is to take an oil sample from your vehicle at the end of a change interval and send it in for analysis. One thing’s for sure though, you basically can’t go wrong with synthetic oil, providing your engine is broke in before use.

*My opinions are just that. It’s likely you’d find 100 people that might agree with me, another 100 that’d be prepared to fight me because I was so wrong, and another 100 who don’t care at all. 2/3’s of those folks are right, I have no idea which ones.

8

That’s actually not what you do then, because your miles are double that of the OP. You would need to change your oil 4 times during a year’s period (6K miles ÷ 1.5K change intervals = 4 changes), with synthetic oil. What you do is what everyone’s done forever, 3K oil changes. No problem with that.

*To be fair, his recommendation was because the OP only drives 3K a year, and if those miles were doubled, my guess is his recommendation would change as well.

9

Also to add if your car is direct injection, some, not all, have a known oil dilution issue where injecting into the cylinder allows gas to get by the rings.

10

Thanks for the opinions, everyone - I suspect I’ll do conventional oil and get oil changes every 6-9 months.

And thanks for the analogy explaining the difference between conventional and synthetic oil.

11

Yes, thanks for the explanation about synthetic oil. Very helpful.

12

In my personal opinion:

I drive less than 10,000 miles a year. I work at home so I do a lot of short trips, but once or twice a month (at least) I go somewhere on the highway that’s at least 20 minutes away. I use full synthetic Mobil 1 oil. Also, it should be noted, I am largely a cheap bastard.

I justify the expense of Mobil 1 over conventional in the following way: Mobil 1, on sale, is between 30 and 40 bucks for 5 - 6 quarts. Conventional oil is between 15 - 25. I use a quality oil filter no matter which oil I am gonna use, so its price doesn’t factor in very much.

Because synthetic oil is more tolerant of “severe” (though in reality this is in no way “severe”) driving conditions, I change it once a year. Mobil 1 says it supports up to a 15K mileage interval on oil changes, but I stick to once a year. I also change my own oil, because it seems like they always get the dumbfucks to do it no matter where I go. The guys who strip out your drain plug, or put the filter on with a wrench and tighten it down such that only a gorilla could get it off by hand (and filters are SUPPOSED to be hand-tightened), or spill shit all over the place.

The extra 20 or 30 bucks for a once-a-year service is worth it to me. And because I do it myself I don’t have to deal with that stupid sticker that says I should come back in 3,000 miles despite the fact that the owner’s manual AND the oil suggest something more like 5,000 to 7,500 even with conventional oils today.

13

To add to the confusion, full synthetic oil used to be full synthetic, this is no longer the case. The standards now come from what a full synthetic can do regardless of if it’s a full synthetic. In other words if the oil passes the standards, regardless of how it is made, it can be categorized with the synthetics. But with that said it also means it passes the standards required.

14

I actually make additive packages for engine oils as my job.

Whether or not a base oil is synthetic does not have any bearing on the change interval. You need to change your oil when the basicity of the detergent in the package is exhausted. All the other additives are in sufficiently high treat rates that their performance is still effective when the detergent base has been neutralized. This includes the sludge formation which dispersants deal with.

Synthetic base oils, because they are more chemically homogenous, do not generate breakdown byproducts at as fast a rate as other base oils. However, the performance tests do not take the base oil into account on the results. So if you have a synthetic oil that is making less breakdown byproducts, that package needs a lower treat rate of detergent and dispersant and whatnot. So the package is cheaper, but that might be offset by the synthetic base oil being more expensive.

Synthetic base oils are better at solubilizing most additives, so that is an incentive for oil companies to prefer synthetic oils. However, the base oil group has a bigger effect on that and on price and availability. What an oil company recommends is based on which base oils they want to produce, and that varies by market – US, Europe, Asia-Pacific, and other regions all differ. Oil companies spec out additive packages based on their desired base oil blend.

Oil companies go to car manufacturers (OEM) and sell performance. The OEM may do some performance testing but usually rely on the data from the blend formulators. The OEM engineers may have preferences for synthetic or not based on their own experiences with performance. That is the factory fill business, which you do not see.

Aftermarket sales – what the dealer or oil change location would recommend – are usually based on the OEM recommendation which is based on which oil company they went with for their factory fill business. But each dealer or oil change location also has its own experiences and may recommend a synthetic with equivalent performance where the OEM only suggests that performance level without specifying conventional/synthetic.

Every step in the supply chain has its own bias in making recommendations, and they don’t always match up. You want the viscosity and performance level recommended by the OEM, and you want to make sure there aren’t any warranty requirements (high-performance engines sometimes mandate synthetic grades or whatnot to for the warranty to be held valid). I personally choose synthetic.

15

Plenty of good answers here.

I’ll add that manufacturers are tightening the tolerrances of the oil used in their vehicles, and polyalphaolefin synthetics are better for a high viscosity index (viscosity drop/ temperature rise).

16

I’m cutting out the choice - I run 0W20 and as far as I know it’s all synthetic.