From my limited understanding of motor oils, semi synthetic and synthetic offer superior performance compared to the “regular” oils.
However, what I also understand is that “regular” oils are good too, as long as you change them regularily (something I do every couple of months).
Lets say a person goes to a semi/full synthetic. It’s going to get just as dirty just as fast as a conventional oil, correct? Doesn’t that then mean that it should get changed at about the same rate?
As well, is there any problems with going to a semi/full synthetic if you’ve been using a conventional for 4 years/40K miles?
Synthetics are highly detergent, and can cause some difficulties with leaking.
A couple of oil changes in and you should be cool, it’s not going to break down as easily nor as quickly; I do changes every 10,000 miles or more, and have the oil tested, it’s always fine. My Ford Probe, which I no longer own but which is still on the road, has now over 300,000 miles and runs fine, and my Explorer has over 100,000 and runs and drives like a new truck. Synthetics are your friend.
Convetional oil, as I’m sure you know, is refined crude oil, and is extracted from the cracking tower at the refinery along with all the other hydrocarbons.
Synthetic oil is generated using one of two processes:
Oil molecules are “built up” from smaller molecules. This is the traditional method used in all synthetic motor oils up till a few years ago, and is still found in some, notably mobil 1.
Natural oil molecules are “cracked” into smaller molecules. This method was pioneered by Castrol for their Syntec line of oils. This method is cheaper than, but possibly inferior to the first method. Mobil sued Castrol over calling Syntec “synthetic” and lost, so most synthetic oils now use this process
So the main difference between synthetic and conventional (dino) oil is that the molecules are smaller. Smaller molecules move around each other more easily, so synthetic is more “slippery”. In addition, smaller molucules are less prone to break apart under stress or “cook” under high heat. Thats what the ads mean when they say synthetic resists “viscostity breakdown”
So while syntetic oil will get just as dirty as conventional oil, it provides better lubrication while under high heat and stress.
If you have a high strung engine, or especially a turbocharger, synthetic oils can be important because the high temperatures in those engines can cause dino oil to break down and lubricate less effectively. You would still want to change it at the same intervals, though.
There is really no problem with going from dino oil to synthetic. However, because synthetic oils can cause rubber seals to swell, it is NOT advisable to go in the other direction. Once you go synthetic, you need to stick with it for the life of the car.
As far as switching now goes, if you change your oil every 3-5000 miles (3 months), you’ll probably never notice the difference, and the extra cost of synthetic just isn’t worth it.
If you have a turbocharger, though, then I’d recommend switching.
If we accept the statement that synthetic oils are better, but the problem with them accumulating dirt remains, it raises the question of whether there’s any way of effectively removing dirt from oil. I can imagine an oil purifier that you use once a month or so, making your synthetic oil as good as new.
Would this idea work? Does anyone know of such a device for use by the average idiot?
Here’s another question… BMW has synthetic oil. The BMW maintenance schedule says the oil should be changed at 15,000 mile intervals. I asked about this (because I had the same questions about dirt), and BMW maintains that this is the proper maintenance schedule.
And a final story for you to chew on. I had a neighbor that never did an oil change. He instead changed the filter every 5,000 miles and added a quart of oil. He never had a problem. Go figure.
There’s quite a bit of confusion regarding engine oils. In fact, the oil’s primary function is TRANSPORTING contaminates (dirt) to the oil filter. You don’t change the oil because it has gotton dirty. You change it because it starts breaking down. As it breaks down the viscosity changes, the antiwear properties diminish etc. Just because the oil looks dark doesn’t mean it should be changed.
Synthetic oil is a much more stable product compared to regular oil, and can therefore be used longer before it needs to be changed. Many change the filter twice before changing the synth oil with good results. Going 10k miles between oil changes is not a problem with synthetic oils.
The big 18-wheelers don’t change oil according to a maintenance schedule. Instead they regularly analyze the oil and only change it when it starts breaking down. There are documented cases of this not happening until after 100k miles in a big-rig running on synthetic!
So used right synthetic oil are beneficial. The oil change interval should be extended. They also survive much better in harsh enveronments such as turbo chargers or hard driving (towing, mountains, speed-racer afficenado etc). If you switch to synth and change the oil every 3k miles you are wasting money.
The concept of oil being a vehicle to transport contaminants is a bit of a stetch, especially in today’s modern engines.
Historically, manufactuing tolerances weren’t all that close, and engine parts would not mate all that well when new. There were burrs and mold lines, etc. in the parts.
The main contaminiant that ended up in oil was metal shavings from the engine parts rubbing together. As the engine wore in, the contaminants decreased, and engine performance usually got a noticable boost.
Cars were typically filled with break-in oil designed to accelerate the process.
This is not nearly the same issue today as it once was, because manufacturing tolerances are so much higher that parts mate well straight from the factory. This is part of the reason why the oil change intervals can be longer now.
However, the longer intervals are as much a product of economics as anything else. Most of the manufacturers who push the longer oil change intervals are the same ones who provider free (pre-paid) scheduled maintenance. (BMW, Audi, Mercedes, etc.) Note that while these cars may come w/ synthetic from the factory, the dealers are more than likely filling them with dino oil.
When I ownded my Audi (a turbocharged car), it was common among owners in the know to bring their own synthetic oil for the dealer to fill the car with, since Audi only paid for dino oil, despite a 10k mile recommended oil change interval.
The concept of oil being a vehicle to transport contaminants is a bit of a stetch, especially in today’s modern engines.
Historically, manufactuing tolerances weren’t all that close, and engine parts would not mate all that well when new. There were burrs and mold lines, etc. in the parts.
The main contaminiant that ended up in oil was metal shavings from the engine parts rubbing together. As the engine wore in, the contaminants decreased, and engine performance usually got a noticable boost.
Cars were typically filled with break-in oil designed to accelerate the process.
This is not nearly the same issue today as it once was, because manufacturing tolerances are so much higher that parts mate well straight from the factory. This is part of the reason why the oil change intervals can be longer now.
However, the longer intervals are as much a product of economics as anything else. Most of the manufacturers who push the longer oil change intervals are the same ones who provider free (pre-paid) scheduled maintenance. (BMW, Audi, Mercedes, etc.) Note that while these cars may come w/ synthetic from the factory, the dealers are more than likely filling them with dino oil.
When I ownded my Audi (a turbocharged car), it was common among owners in the know to bring their own synthetic oil for the dealer to fill the car with, since Audi only paid for dino oil, despite a 10k mile recommended oil change interval.
Correct me if I’m wrong, but I believe oil has a dual role: 1) lubrication, 2) transportation of particulates.
#2 is accomplished through the use of detergents. The idea is that dirt will be suspended in the oil with the aid of detergents, then later captured in the oil filter.
backing up a little bit… some oils use detergent. Some do not. If your engine has an oil filter, you should use oil with detergent for the reason stated above. If your engine does NOT have an oil filter (such as a small lawn mower engine), you do NOT want detergent in your oil. Why? The detergent in the oil will suspend the dirt, and because there’s no oil filter to capture it, the dirt will grind away at the metal interfaces. Not good. In an engine without an oil filter, you want the dirt to simply fall to the bottom of the crankcase, which is accomplished with oil that does NOT contain detergents.
Excuse my cynical response. I’m a little amused at people who pay a premium for motor oil that makes the engine last longer, and then trade for a new car every 30000 miles. An engine might very well give that much use with any oil and no oil changes.
Here’s my opinion, and I have no facts to back it up (that’s why it’s an opinion): For almost all cases, putting synthetic oil in your automobile engine is a waste of money. I think it’s much smarter using standard motor oil and changing it (and the filter) every 3000 to 6000 miles.
But I do use synthetic oil… in my riding lawn mower. The engine is air-cooled, and thus gets pretty hot. (It also has an oil filter; see previous post). To me, it makes sense to use synthetic oil in an air-cooled engine….
Crafter_man: Touche. Of course the primary role of oil is lubrication.
I still stick to my guns in that as long as the oil is still stable, and the additive package has not broken down, it does not have to be changed. It may look quite black, but that by itself is not an indication of whether it is still good or not. Only oil analysis can determine if the oil is still good.
Several posters feel synth is a waste of money. I agree, partly. Let’s take an average driver in a mild climate. Temps swing from maybe 30’s to the high 80’s. The car is used to haul the owner and family members to work, church, whatever. The car is just your basic family hauler, never sees over 4000 rpm and has no turbo charger. Does this car benefit from synth? Nope.
Now a car operated in extreme conditions (prolonged temps well below freezing, or above 100F) will often live longer on synth. If you also add in a car that is of the sporty kind and a driver who likes to floor it running it up to 5, 6, 7 thousand revs every now and then I expect noticeably reduced engine wear with a good synthetic oil. With a turbo charger I feel synthetic is pretty much mandatory.
For those who don’t believe me I wish you could see some of the engines I’ve taken apart… The cheap regular oil that was used in them coked and formed hard solid chunks all inside the engine. This is regular oil breaking down from heat, something a good synthetic oil will not do. High quality regular oil is not as prone to this as the cheap stuff, but will never be as heat resistant as synthetic.
I should have pointed out that my diesel is a turbo, so synthetic oil is recommended, as zwede says. But a quality natural motor oil, properly used, will keep it running just as well just as long, IMO. Synthetic takes some of the worry out of it for me.