Friday, April 22, 2011

Oil: Why you should probably be using synthetic

One thing that I am frequently asked is should I use synthetic oil or not in a vehicle. In almost every case the answer is yes. I use synthetic in all of my vehicles including the old Bronco II. Synthetic oil in general is better than non synthetic because of:
  • Higher film strength
  • Better resistance to oxidation
  • Better cold flow properties
  • Better stability at higher temperatures
  • Higher detergent content
  • Longer drain interval
  • Lower Friction
I frequently hear two complaints against synthetic oil. The first is that it will make your vehicle leak oil or leak more oil than it currently does. The truth is it isn't the oil that makes it leak it is that it cleans out all the crap that was plugging leaks in your engine. So if you have a vehicle that is older and has dried out gaskets it will probably start leaking. It would have started leaking eventually and gaskets are cheep. The other complaint I hear is that it costs more. This is true but you can go to a longer change which usually makes to total cost per mile the same or less that that when using conventional oil. 

Why is higher film strength better?
Film strength is the force needed to push through the film of oil to have metal to metal contact. This higher this is the better protected from wear parts are

Why is better resistance to oxidation important?
Being better able to resist oxidation prevents the oil from breaking down over time. As oil oxidizes its ability to lubricate goes down as it is no longer oil. For those who don't know oxidation is just like burning, except burring is very rapid oxidation.

Why is better cold flow important?
Cold flow is the ability of something to flow like as liquid when cold. The lower temperature oil flows at the colder a vehicle can operate at. Also being able to flow better a cooler temps allows oil to circulate and flow through the engine faster on start up.

Why is better stability at higher temps important?
Heat can cause oil to break down in to other molecules. Some of these molecules could be solvents that thin the oil, some could be tars, some are gases that just escape. This is similar to what is done in oil refineries when they take crude oil and make different thing out of it.

Why is higher detergent content better?
Some may not think this is a good thing as this is what usually causes your engine to leak oil when switching to synthetics. The truth is that this will clean out the crud and crap that has built up over time. If you have seen the Ford commercial where they have the engine that is filled with black stuff that is sludge. It will build up over time and restrict oil flow or prevent oil from getting to moving metal surfaces. Higher detergent contents help clean this out. This is also the most important reason why changing oil regularly is important.

Why is a longer drain interval better?
This should be simple, you don't spend as much on oil. You also don't consume as much oil. Previously when using standard oil I would typically change oil at 2,500 miles, with synthetic I typically change it at 5,000. I have heard of some people going as much as 12,000 to 15,000 between changes but I just can't seem to force my self to go any were near that long. I have gone as much as 7,000 when I couldn't get to it for about 2 and a half weeks and it didn't look much worse than it does when I change it a 5,000.

Why is lower friction better?
Friction is the amount of energy to move one thing across another. By lowering the friction in your engine it takes less energy to move all the moving parts. This means that you get better fuel economy and also your engine produces more power. It makes your engine more efficient.

When you shouldn't use synthetic oil
There are few cases where I wouldn't recommend using synthetic oil:

  • Your car already leaks oil and it leaks from engines seals not gaskets. If you use synthetic oil you will just leak even more oil.
  • You have an older engine that is worn. Here you will just burn lots more oil than you already do
  • You are doing an initial engine break in


  1. Do you know anything about Amsoil? I've started using it this past year, and it's rated for 25,000 or 1 year (it can be check at that time and may still be fine). My mechanic says he's had people go as long as 30,000 miles before needing to have the oil changed. I've been pleased with it so far, but if it's really so good, I don't know why more people aren't using it.

  2. I am familiar with Amsoil. It actually uses group IV base stock which is also used by Mobile and some others. There are other groups of base stock typically group III (in europe this isn't considered synthetic oil and is used by a number of manufactures) or group V which sometimes is ester based (used by RedLine) but generally is used as a catch all for synthetic oils that aren't made from group III or IV base stocks. The biggest benefit that I am aware of with group V ester based oils are less volatile than other oils, meaning that they have a higher vaporization, flash, and smoke points, additionally ester based group V oils tend to naturally do more cleaning than group IV or group III oils. Even if the oil is good to 25,000 miles (Mobile 1 also makes a product that they claim lasts that long) you will still need to do a filter service since unfortunatly no oil prevents all deposits or lubricates perfectly. My one main beef with Amsoil is the people who use it are fanatical about it almost like it is a religion. I have used Amsoil products and have been in general pleased with them, but I also typically use Mobile 1 for my motor oil as I can usually pick it up for around $4 a quart when it is on sale and then I stock up. When I tried Amsoil as my engine oil it came out looking similar to the Mobile 1 I typically use so it didn't seem better. I run Amsoil Synthetic Multi-Vehicle ATF in my transmission since they are willing to stand behind their synthetic ATF for my transmission (97 BMW 540i with the ZF automatic transmission with a factory fill of ESSO LT 71141) unlike Mobile 1 which does not reccomend using their synthetic ATF for this application.

    Unless your mechanic also has a full oil analysis lab in his shop I would suggest doing regular 5000 mile changes instead of just trusting that the oil is good. You can have a 3rd part lab do an engine oil analysis to check the oil but I think this costs a between $100 and $200 to get done, but I could be completely wrong. I would love to see some independent testing done that wasn't paid for by the manufacture. I know this link isn't about engine oil but is about transmission fluid, but it shows the results of a fluid analysis for BMW's lifetime ATF (ESSO LT 71141). If you read the whole discussion thread the individual who posted the fluid analysis has a few follow ups later on after several additional partial changes.

  3. Amsoil has a proven track record with people who experiment with turbines (jets etc). Mobil I's performance is poor in turbines that run hot and people had failures (seized shafts) where the same turbine would run just fine on Amsoil. I'd advise against Mobil I in turbocharged cars -- of course it's better than dino oil, but with a turbo Amsoil has demonstrably better performance.

  4. Well Kuba you seem to have shown that you don't know much of anything if you believe that the turbo charger in your car is similar to the turbines used a jet engine or lets take it ones step further the turbine in a combined cycle turbine in a power plant. The temperatures, speeds and forces in that tiny turbo are nothing compared to those in a large turbine. Also there isn't any combustion occurring inside the turbo on your vehicle like there is in a jet or power plant unless you have a really poorly running engine. Although given the number of ricers I see that blow black smoke when accelerating there are probably a lot of turbos that have active combustion occurring in them. The biggest problems with turbos is that people don't let them cool down before shutting off the engine to prevent oil vaporization. You really should let the engine idle for a minute or so thus allowing the oil to circulate through the turbo and cool them down. If you are really worried about oil vaporization then I wouldn't recommend Amsoil or even Mobile 1 but would instead recommend running Red Line as they use group V base stock (a catch all of things that aren't group II, III, IV) and are ester based. These are substantially less volatile than any of the group IV or III based synthetic oils. The ester based part is what is important as there group V base stock is used as a catch all. Also a turbo experiences the exact same heat as the cylinder walls, pistons, and exhaust valves do, but is more thermally isolated as it doesn't have a large block of metal to dump excess heat into so they take longer to cool. The longer cooling is why you need to let the vehicle idle for a bit before shutting it off because you need to dump the excess heat into the circulating oil.

    I might be a bit more friendly towards Amsoil users if they behave like cult members and didn't drive crappy running trucks with Amsoil stickers plastered all over them that sound like diesel but were actually gasoline powered. I don't see how that is a good advertisement for a product you are trying to sell. Also I find it hard to justify the price difference even using the extreme extend drain interval since it isn't just a few dollars more but closer to 3x the price of Mobile 1 extended drain which claims a similar life to Amsoil. As I said previously I am using their ATF in my transmission as they are willing to stand behind it for that application but I don't think it is the miracle in a can that the true believers think it is.

    Also no oil is perfect, oil does a lot more than lubricate as it needs to hold combustion products like carbon in suspension and neutralize acids that also are created in the combustion process (these are what causes your oil to break down and what causes most of the "dirt"). No oil is a perfect lubricator as there is still friction and no oil has a near infinite film strength. If we had an oil that was a perfect lubricator and had infinite film strength then automotive engines would have a carnot cycle efficiency closer to or possibly over 40% and would never wear out.