Basic properties of synthoils
Synthetic oils differ from “regular” petroleum oils in that they are
engineered from specific base stock to have superior performance. Their polymer chains (the parts which provide the actual lubrication) are
stronger and resist breakdown much longer then petro- oils under conditions of mechanical wear, high heat, and contamination by foreign elements – all of which are found inside car engines.
Synthoils will simply last much, much longer inside an engine because they don’t break down as fast at petro-oils. Semis have reported running over 100,000 miles on a single oil change while having the oil chemically analyzed at regular intervals to assure it is still capable of performing its functions. However, running oil to this distance requires superior filtration and regular analysis.
Another issue is volatile elements. Petro-oils and synthoils both have heavier and lighter (more volatile) elements. Under heat, the petro-oils “volatilize” (give off the lighter components much faster). This increases the oil’s viscosity and contributes to its breakdown. Synthoils are much superior in this respect as well.
It is very important that synthoils (unlike petro-oils) leave a lubricant film on metal surfaces, providing better lubrication at start-up. They also are much less affected by low temperatures than petro-oils, making it much easier for your engine to turn over and start on cold days.
Not all “synthetic oils” are totally synthetic. Many brands combine part petro-oil and part synthetic stock to hold the cost down. These oils cost less than true synthetics and are superior to regular petro-oil, but inferior to pure synthetic oils. Check the labels to be sure what you’re getting; it may make sense to use a blend if you’re short on money, if your car has high oil consumption or if you insist on frequent oil changes, but want some of the advantages of a synthetic oil. The leaders in pure synthoils are Amsoil, Red Line and Mobil 1, although many others have entered the market recently. However, many of the late entries are blends.
New Cars/break-in period
Synthetic oils are more “slippery” than standard oils. Because of this, no manufacturer I am aware of recommends running synthoil during break-in, as it can actually prevent the wear necessary to keep piston rings from seating. The best tactic according to “common wisdom” is to run a good grade of petroleum oil (whatever the manufacturer recommends for your car and climate – it’s in the manual…) for at least 1000 miles, preferably longer, before switching to synthetic oil. This allows the rings to seat fully. During the break-in, I like to change oil and filter at 500 miles, 1500 miles, and again at about 5000 miles, switching to synthoil at the 5K mark.
Be aware that if you change to synthoil in a new car, you must still change oil and filter at least as often as the manufacturer recommends in order to keep your new car warranty in force. Since this interval is 7500 miles in most cases, you at least will get your money’s worth out of the synthoil and can feel good about being able to run 7500 miles with confidence your oil will hold up well. (Most car aficionados do not run petroleum oil more than about 3K miles between oil/filter changes.)
Used cars/changing to synthoil
The decision whether to run synthoil in a used car is primarily economic,
based on oil consumption. (Sludge buildup is also a factor – more on that later.) If your car burns a quart every 500 miles, it’s not a candidate for synthoil because it’s just too far gone. Change over after a rebuild. However, IMHO, if the car goes 1000 or more miles between quarts, it is a candidate for synthoil. Many high performance cars, especially V8s, will burn a quart at 1K intervals and it may not indicate engine problems (my ’66 GTO comes to mind…). Whenever you change to synthoil, you can usually expect that your oil consumption will stay at its current level and not increase for a long time, as the engine will generally not wear very fast on synthoil.
To change over a car: first, pull a rocker arm cover and look to make sure it does not have a heavy sludge buildup. All synthetic oils are very highly detergent and will break up any sludge or deposits in the engine. For this reason, heavily sludged or very old engines with deposits are not good candidates, as you really don’t want to break all that stuff loose to plug up your oil passages.
Having determined that the car does not have sludge, add a quart of a good “engine clean-out” treatment and use it as per the instructions. The goal is to get the inside of the engine as clean as possible before changing over. After the treatment, change the oil and filter containing the cleaning agent.
Install a new filter and synthetic oil. If you can buy a filter superior to standard ones (aftermarket filters are available which offer better filtration than standard filters) do so, because it will allow you more protection during your extended change intervals. It’s a good idea to run the first change of synthoil for no more than 3,000 miles, then change oil and filter again, because it’s sure to dissolve deposits your engine cleaning treatment did not get.
Oil change intervals
This is the most controversial aspect of using synthoils. Because most of them cost $5 per quart or more, it gets very expensive to change them as often as petro-oil, and it’s not really necessary. However, car engines are subject to condensation and accumulate particulate matter, both of which contaminate the oil. If you want to extend your oil change intervals, do your homework on both air and oil filtration.
Air filtration affects the particulates which enter the engine, and the oil filter is your only defense against particulates and contaminants. Major aftermarket brand names in filtration include Amsoil and K&N, and web searches will provide information for you. (This is not a brand pitch – but you have to know what to look for.) Amsoil says you can run their synthetic oil one year if you also use their oil and air filtration; they also sell kits you can use to have their lab test your oil if you want to see how far you can run it before it actually needs to be changed.
For many years, I have run each change of synthetic oil for a year, changing the filter at six-month intervals. That’s my own guess at what’s reasonable for me, running a used car about 10K miles a year.
Gear lubricants for automatic and manual transmissions and rear ends are superior to their petro-oil counterparts in two ways. First, they offer less mechanical resistance to gear movement, especially in cold weather, where they are vastly superior. This results in easier shifting in the cold, and some users report improved gas mileage (both from oil and from gear lube…). Second, they break down more slowly, so they provide good lubrication longer.
In automatics, synthetic ATF’s highly detergent qualities keep varnish from building up, extending transmission life. The ATF also resist breakdown under heat better than petro-ATF, giving you more “grace period” to discover mechanical problems.
In manual transmissions, synthetic lube makes shifting easier and reduces mechanical resistance to the gears moving. Note: you must put the correct synthetic gear lube in a manual transmission or it may grate when shifting gears. The synchros in your transmission are brass rings which require a certain amount of friction to function. If you put in a synth-lube not made for transmissions, the synchros may not be able to work properly due to their friction being reduced too much…resulting in grating gears when you shift. A synth-lube made specifically for transmissons has friction agents designed to allow proper shifting. This is a case in which transmission gear oil and rear end gear oil are NOT created equal.
In front wheel drive transaxles, synth-lube has been the standard for years. Make sure to get the right lube for yours. If you doubt the wisdom of using it in transaxles, ask an Audi mechanic. Enough said.
Situations indicating use and non-use
When to use synthetics:
When an engine is in good shape, not burning oil excessively
When you will keep the car for some time
When you want some “edge” to prevent engine and transmisson breakdowns
When you are comfortable with extending your oil change intervals to get
a $$ advantage
When not to use synthetics:
When the engine is burning more than one quart of oil per 1K miles
When the engine is heavily sludged, making it impossible to clean
When you plan on selling the vehicle in a year or two
When you can’t afford the cost. (In this case, change petro-oil and filter often!)
Why doesn’t everyone use synthoils?
Because people resist change, and “they’ve used reg’lar oil all their lives!”
Because most people aren’t really in tune with their cars and how they work.
Because synthetics have really only been a factor in the marketplace since 1970 or so.
Because synthetics cost more money to buy.
Because most people really don’t understand how cars work and what the advantages are.
But in the last five years, almost every major oil manufacturer has brought out a synthetic oil, and in the near future, cars will be designed to run on them exclusively. Example: Since the 1993 model year, the Corvette has required owners to use synthoil to keep the warranty in force!