Which is better - synthetic or conventional oil?

[bailadora]

My minivan is getting up there in terms of mileage and I'm starting to wonder if I should switch from conventional oil to synthetic. One thing that makes me hesitate is the difference in cost. Paying almost double what a conventional oil change costs makes my wallet whimper. But... I also recall once reading that synthetic oil was better for engines with high mileage. I can't remember the reasoning, just the claim itself. I'm hesitant to ask at my local oil change place, because they're ALWAYS trying to upsale me on something. Yes, I know that's how they make their money, but it annoys me just the same. The only reason I keep going back is because the convenience of proximity.

Anyway, I thought I'd throw the question out there and see my fellow Litsters have to say. And if anyone is a mechanic or is particularly good with car engines, please feel free to add your expertise!

For what it's worth - I follow conventional wisdom and have my oil changed every 3000 miles. My vehicle is 11 years old and has about 180K miles. My current plan is to drive it until it gives up the ghost. As far as driving habits, it's typically city driving: stop and go as I run errands, take the kids to activities and whatnot. The only time we do any real highway driving is when we head out for our summer roadtrips to see family in other parts of the country. If there is any other information that I left out that might be helpful in tailoring the advice, please let me know. As always, thanks in advance for the assistance!

 

[albertaboy]

Synthetic lasts longer, but is about twice as expensive.

 

[bailadora]

Synthetic lasts longer, but is about twice as expensive.

Yeah, I've read that. I guess what I'm having a hard time discerning is if it's truly much better for vehicles, especially ones with the particular characteristics I mentioned. Based upon the little bit of research I did, it seems to be inconclusive.

 

[NippleMuncher]

I've seen some impressive claims on synthetics, but have never tried them myself. What I would recommend is to ask your regular mechanic what the differences are and if your vehicle could significantly benefit from the added expense.

Basically, it sounds like you're getting to the end of life for your van at 180K. Is doubling the cost of oil changes going to give you noticeable benefits? My suspicion is no, but I am certainly not in the trenches to be certain.

 

[ayrton]

I always use synthetic oil, but mainly because my BMW dealer is quite distance away. I change every 6 months. That said, with a high mileage car I'm not sure the extra cost would be worth it unless you like the idea of changing less often. Not only is that more convenient, but the costs average out. Also the synthetic oil will protect better.

 

[MTChevy]

I am a mechanic for a living, and i will say if your good at changing every 3k stick with conventional. If you dont feel like changing it as often go synthetic and with a good filter run it 5k miles and change it.

 

[Missingout]

I used synthetic on my sport bikes and would on all high performance vehicles.
Regular is fine on your everyday car/truck.

 

[billrichards41]

Use regular oil. Change it and the filter at the 3k interval and your car should be fine all other things considered.
All you would do is throw away money and see no benefit at all.
As for why I say this, I have both types of vehicles and an engineering degree. Unless you upgrade all the components, filter and engine; your car was designed to use normal oil.
Synthetic oils breakdown slower, meaning losing their viscosity or ability to lubricate. Regular oil if changed on the 3k interval and even out to 5k under normal use are still just as good doing their job. The main reason you change it is due to the contamination of the oil not the lubrication it offers.
So unless your engine is a high performance engine with high reeving and fine tolerance the synthetic offers you no advantage. It's money down the drain.

 

[jehoram]

Use regular oil. Change it and the filter at the 3k interval and your car should be fine all other things considered.
All you would do is throw away money and see no benefit at all.

I agree with this, except that for modern engines and modern oils and ordinary driving conditions, five thousand miles is a good interval; anything more frequent than that just wasted money and oil.

If the engine has a lot of wear, it may make sense to go to a higher-viscosity oil.

 

[billrichards41]

I agree with this, except that for modern engines and modern oils and ordinary driving conditions, five thousand miles is a good interval; anything more frequent than that just wasted money and oil.

If the engine has a lot of wear, it may make sense to go to a higher-viscosity oil.

True 5k is fine, but she does have high mileage and is stop and go, but still 5 k is okay even than, spend the money on a quality filter and it is fine.

 

[sunkissedblues]

Been putting synthetic in my truck ... and just passed the 240k mile mark on that. Just sayin'

 

[bambikiller]

I always heard the conventional oil is the best until a 100 K then switch to synthetic.

 

[whywouldi]

Why does everyone still believe that you have to change your oil every 5k miles ? My Honda tells me when to change the oil, and it is at about 15k miles (although I use my car mainly on the highway).

 

[njlauren]

Based on experience you prob will want to stay with regular oil and simply change it at regular intervals.Changing it at 3k could be overkill (according to a paper cited in one of the car magazines that was written by the SAE, as far as they figure it out the 3k oil change was invented by Jiffy Lube as an advertising slogan, that unless you are driving in high heat and/or dusty conditions that is just a waste of money). Modern car engines have oil change intervals in the 7500 mile range (varies, some cars it is higher, synthetic oils last longer, some a bit less) but 5k on a city driven minivan is fine. There are oils supposedly designed for higher mileage engines that probably won't hurt, but the big thing with a relatively high mileage engine is simply changing it at regular intervals. You can put a bottle of oil treatment in every fill up or what they used to call motor honey, but if the engine is otherwise fine, I would simply change the oil at 5k intervals.

Synthetic oils are good products, in high performance engines or high load engines like a working pickup truck they may be worth the extra cost. One myth that used to be out there is you can't switch between synthetic and mineral oils (either way), and that is just that. The myth was the engine broke in differently and if you then switched, it would cause damage, which tells me it is someone who doesn't understand much about how engines work.

 

[vkane68]

Sounds like you have taken good care of your vehicle and if anything the 3000 mile oil change interval is a bit conservative with an industry average change interval of 7500 miles for modern engines. As others have stated you could easily go to 5000 mile change intervals with conventional oil without a problem and save $$$$. While synthetics can have advantages such as increased resistance to thermal breakdown and increased longevity there is only a payback if you significantly increase the oil change interval. Companies like Amsoil advertise the payback of their synthetic products occur because it is safe to extend oil drain intervals out to as far as 20,000 miles or more (under certain conditions). Many have successfully implemented extended drains but controversy over the financial viability of synthetics exists because the cost of the oil is as high as $10 per quart (or more) and the limit on extending the change interval is the ability of the oil to keep soot and combustion byproducts in check. This can require oil boosters to revitalize the oil chemistry and bypass filtration to remove contaminants. In many cases it is much simpler, and way cheaper, to just use conventional oil and change it more often.

With 180K miles on your vehicle a change to synthetic oil will not significantly increase the lifespan of the engine and in some cases the improved film strength of synthetic oils can overwhelm worn high mileage engine seals and cause leaks.

My recommendation is to continue to use conventional oil in your vehicle with a quality filter and change it based on the manufacturers recommended interval. Leave the synthetics for vehicles that need them due to operating/engineering requirements or big rigs that do so many miles that extending change intervals makes economic sense.

 

[NippleMuncher]

Why does everyone still believe that you have to change your oil every 5k miles ? My Honda tells me when to change the oil, and it is at about 15k miles (although I use my car mainly on the highway).

I have been a 3500 mile kind of guy from the time I could change the oil in my dads truck (preteen ). When I started buying my own trucks which were primarily work horses, I've stuck with that. When I retired from the need of a work truck and now have a daily driver truck that only sees grocery runs, I don't disagree that longer intervals are suitable. There have even been a number of authorities vouching for longer intervals. The thing is, my daily driver truck is STILL programmed to tell me when it's had 3500 miles since its last oil change.

Because this is a daily driver, I'm not the stickler for the 3500 mile mark as I once was, but as was said earlier, it isn't that the oil has lost it lubricative properties, it is the pollutants within the oil that are damaging. I say that if you pull the dip stick and the oil is so black that you can't see the dipstick beneath it, then it's time to change the oil. If you can still clearly see the dipstick, then you may want to reconsider your oil change intervals.

 

[ayrton]

BMW suggests synthetic every 15K or once a year. I found that kind of worrying, so I do it every 6 months. I also have a Nissan 370z sports car and they recommend synthetic every 3 months for what is considered more or less short trips and around the city driving. Who do you believe? I think 3 months is rather excessive for synthetic.

 

[njlauren]

I have been a 3500 mile kind of guy from the time I could change the oil in my dads truck (preteen ). When I started buying my own trucks which were primarily work horses, I've stuck with that. When I retired from the need of a work truck and now have a daily driver truck that only sees grocery runs, I don't disagree that longer intervals are suitable. There have even been a number of authorities vouching for longer intervals. The thing is, my daily driver truck is STILL programmed to tell me when it's had 3500 miles since its last oil change.

Because this is a daily driver, I'm not the stickler for the 3500 mile mark as I once was, but as was said earlier, it isn't that the oil has lost it lubricative properties, it is the pollutants within the oil that are damaging. I say that if you pull the dip stick and the oil is so black that you can't see the dipstick beneath it, then it's time to change the oil. If you can still clearly see the dipstick, then you may want to reconsider your oil change intervals.

That is very good answer and there is always a caveat with oil change intervals, even the owner's manuals tell you that the rated miles between changes is under ordinary driving conditions, that under heavy load, extreme heat or in dusty areas you may need to change it sooner. With a high mileage engine, if the rings are starting to fail it is possible the oil will get filthy faster. The basic test would be at 3000 miles check the oil and see the color, and if it is dark at 3000 miles, change it; if it takes till 5k to do it, change it then. You won't do any damage to the engine changing it at 3k, just might be paying more then you need to.

The other thing with service intervals is the number of months it takes to make that level. 5k miles with someone doing typical driving might take someone roughly 5 to 6 months, but if you are someone that puts something like 500 miles a month, it might take 10 months to get to the 5k, and your oil could get filthy earlier then 5k, especially if your driving is short duration, stop and go city driving). I would still check the oil maybe weekly, and if it gets dirty before the 5k interval, change it and this would be especially so if you aren't putting a lot of mileage on the car. My van is roughly the same age as yours, and that is what I do.

 

[Que]

we've had this debate on a car form that I belong to over and over.... 1 thing that seems to be a consensus says whatever you been using use that.... synthetic is the best to use on a brand new motor and, haven't always used synthetic then it will always be contaminated by the dinosaur oil in there.

the benefit to synthetic oil is all of the molecules are all the same size. the carbon chains in dinosaur oil tend to be larger and irregular as they are naturally occurring. some people think it on older engines dinosaur oh is actually better because all the various size molecules each find a little nook and cranny in your engine that they fit exactly.

 

[warrior queen]

Lucas heavy duty oil stabiliser.
It's a product made in the USA, and we add it to all our cars - one car is 30 yrs old, one is 26, one is 10yrs and the last is 9, but has a brand new engine.
We use it in the diffs too.

 

[njlauren]

we've had this debate on a car form that I belong to over and over.... 1 thing that seems to be a consensus says whatever you been using use that.... synthetic is the best to use on a brand new motor and, haven't always used synthetic then it will always be contaminated by the dinosaur oil in there.

the benefit to synthetic oil is all of the molecules are all the same size. the carbon chains in dinosaur oil tend to be larger and irregular as they are naturally occurring. some people think it on older engines dinosaur oh is actually better because all the various size molecules each find a little nook and cranny in your engine that they fit exactly.

What you are saying about synthetic and dinosaur oil (I like that term, have to remember it) is true, synthetic oil is consistent molecularly whereas oil from the ground is something made by millions of years of pressure and heat from a variety of organic material, so it wouldn't be consistent.

On the other hand from what i know of both chemistry and the materials of engines and the mechanics of lubrication, I doubt whether dinosaur oil 'fits' any better or the like. In terms of lubrication, the lubrication value of a synthetic or dinosaur oil is the same compared in the same oil SAE classification type (the guy who is the engineering editor at Road and Track has done articles on lubricants, he is a member of SAE and a mechanical engineer).

Synthetics have advantages, they don't break down as much under heat load and they are better able to dissipate impurities, which is why they have longer service intervals. High powered sports cars and the like specify synthetic oils because with the unique load characteristics of those engines, from what I have been told they are afraid owners would not change mineral oil lubricants enough and damage the engine, plus those engines tend to run hotter then a typical production engine, especially if someone has a heavy foot.

For most production cars, I would say that it comes down to a matter of economics, if the cost of synthetic oil with a longer service interval is cost equivalent to let's say 3 changes of regular oil, then it might be a good thing.

As far as dinosaur oil 'contaminating' synthetic oils, I don't think there is much truth to that, I think it is an old wives tale that is based in some fact, that when you change the oil in a car there is still some oil left in the engine, roughly between a pint and a quart. Given that you put 4 to 5 quarts in the engine, the 'contamination' factor is not likely to be that high, I would be willing to bet that if you tested the oil that was 'contaminated' for things like thermal breakdown and the like, you wouldn't see significant differences.
For most people's driving experiences in typical cars, wouldn't matter much at all I suspect.

 

[bailadora]

Lucas heavy duty oil stabiliser.
It's a product made in the USA, and we add it to all our cars - one car is 30 yrs old, one is 26, one is 10yrs and the last is 9, but has a brand new engine.
We use it in the diffs too.

Damn! Now that's what I call longevity! How often do you add the stabilizer?


Thanks for all the excellent information, everyone. It sounds like the synthetic oil won't significantly extend the life of my engine, so I think I'm going to stick to dinosaur oil (I like that term). Although...NJLauren - you keep talking about high heat conditions. What exactly does that mean? Do you mean engines that run particularly hotter than others? Hotter climates?

 

[TheOne007]

Synthetic Oil is by far more superior than Conventional Oil (dyno oil). I know you are paying higher for the synthetic, but it's worth it in NEW engines. Honestly, check your owners manual or under the hood. Some manufacturers will only allow certain brands because of the rating of the oil (generally Mobil1). Since your vehicle has 180k, I would stick with Conventional, or run the High Mileage Oil (semi-synthetic). Bobistheoilguy has good write ups on viscosity and thermal break downs on oil. I personally run a Semi-Synthetic in a 110k mile Honda V6, and I run conventional in a 50k mile Lexus. I run Castrol Edge Full Syn in my 45k sports car. If you have motorcycles or ATV's, I run AmSoil. I was having trouble with my manual transmission Acura, and I switched to AmSoil Syn for the trans fluid, and it fixed and improved my shifting like non other. I'm not a fan of Royal Purple (this may be fixed, but I haven't kept up like I have in the past) they have higher amounts of abrasives in their oil that can ruin crank bearings and score them.

If you are having severe oil loss, or leakage, putting EngineStopLeak or oil thickeners will make your engine tear itself apart. You have major internal issues. Today's Conventional Oil can almost be pushed to 7.5k, I wouldn't recommend, I do not go more than 5k anymore.

 

[warrior queen]

Damn! Now that's what I call longevity! How often do you add the stabilizer?

The 30 yr old car is running a 1971 Windsor engine.
We add the stabiliser with every oil change... 5000km.

 

[RandomAssGuy]

I've been working on and racing cars for close to 15 years now (building and swapping engines, transmissions, axles, you name it) and in my opinion and from experience making the switch to synthetic on a high mileage motor is asking for trouble.

It can lead to burning more oil, or oil leaks. They tend to clean out the motor a bit better but the problem is it cleans up the gook helping keep your gaskets sealed up. If you ran synthetic from the beginning it would keep the seals in good shape and you wouldn't really have the problem to begin with.

Synthetic is great stuff. I run it on anything I run hard (pretty much everything I own) and it keeps everything in the best shape compared to a standard oil. Switching a high mileage vehicle is a bit of a gamble and really somewhat useless in my opinion. If you wanted the gains in engine life synthetic brings it should have been used before it started to get worn out with the mileage and conventional oil. You will gain some extra life, but not nearly as much at this point. The risk to reward balance is off on a high mileage motor. You have one of the main seals or a pan gasket or something start leaking it can get pricey to fix.

Keep running a quality conventional oil, and most importantly a quality oil filter. Never let anyone put an orange oil filter on your vehicle. Run from anyone that want's to put one your car. Fram filters are junk and tend to come apart internally and bad, bad things happen.