Synthetic Oil vs Mineral Based Oils & Lubricants ...

This is an excerpt from the Montero Sports Rock's Message Board on synthetic oil versus normal mineral based oils and lubricants. Some good information as well as connecting link(s) to other sites. The following points are discussed for both synthetic and mineral based oils:

  • Resistance to contamination
  • Thermal resistance
  • Change intervals
  • Resistance to break down under pressure

The conversation follows ...

Normal oil VS synthetic oil
on: Feb 22nd, 2002, 2:05pm

Would you recommend using a normal oil or a synthetic oil? For a oil change?

Re: Normal oil VS synthetic oil
Reply #1 on: Today at 2:15am

I am using Mobil 1 synthetic on my 2k ES. As always, there are pros and of one product. Below are just some benefits of using synthetic over mineral-based oil, which I cut and paste from my research on Internet.
1. Synthetics prevent start-up engine wear and are pumped to critical passageways, surfaces and bearings much faster than mineral-based oils. With mineral-based oils your engine is basically running with no oil (which can be as much as 20-30 seconds, depending on the severity of cold weather, after cranking the motor). With synthetics after several hundred thousand miles you still will have a strong running engine, instead of a used-up engine that requires a re-build. This has been proven by millions of miles of customer usage and countless laboratory and field tests.

2. Added slipperiness is another attribute of synthetics. The uniform diameter of synthetic oil polymers allows them to more easily slide over one another. The resultant reduction in friction shows up as more horsepower and torque and reduced internal engine wear.

3. Synthetics have a much higher resistance to heat than mineral-based oils.
Also, with synthetic in the engine I can have the oil change every 5k - 7.5k miles instead of 3k because synthetics resist oxidation and thermal breakdown, which will also inhibit the creation of varnish and sludge and provide better lubrication for longer periods of time.

In summary, the biggest draw to synthetics is their increased lubrication and the longer drain interval.
4x4 Extreme Sports
Re: Normal oil VS synthetic oil
Reply #3 on: Today at 5:05pm

Those quotes of ********'s are correct. Missing one thing, though. Synthetics ALSO "cling" better then mineral based oils. The best analogy I've found is synthetics behave like plastic "cling wrap". ie. SaranWrap, etc. Yea, sounds goofy, but when you shut an engine off all the oil tends to run off the parts. Strictly mineral based is the worst, blends are better but 100% synthetic actually "sticks" to the parts better. This is critical because most of you're engine wear happens when you start the engine. The likelihood of metal to metal contact is much greater since the majority of the oil has had a chance to run back down into the sump.

I've seen this in a very simple way: Try to wash synthetic oil off of anything. Even your hands. Its like having a plastic coating on what ever it gets on. I'm STILL trying to get this stuff off my bumper where it drained out during my little tip-over incident in November.

Currently, I have 120K+ on my '97 Sport. Have been running synthetic since I bought it in everything. Diffs, t-case, transmission and engine. Amsoil in the drive train and Mobile 1 and Valvoline in the engine. Those that know me know that this vehicle is NOT treated kindly. EVEN with 35" Geolandar M/Ts and the axle conversion to Dana 44s front and rear I get 17.5 to 18 MPG in town consistently and the vehicle passes emissions better then it did when it was new and unmodified. That is NOT a trademark of an engine that is wearing out!

One more thing that was only partially mentioned, heat, and another thing that wasn't mentioned at all. Load. I don't have the molecular diagrams in front of me - probably a good thing.:-) But, synthetics can take a LOT more heat before they start to break down molecularly. Once a molecule breaks down, its lubricating ability is gone. Heat speeds this process up - one CRITICAL reason you're supposed to do oil changes. Even if you can keep it pure - impossible, of course, since contamination from blow-by (exhaust and air/fuel intake mixture past the rings into the crankcase) is impossible to eliminate completely and so is carbon build up internally - oil breaks down molecularly over time.

Load or pressure put on the molecular structure of the molecule. If I remember this correctly its called the "sheer point". The pressure point at which the molecule breaks down. (someone correct me if I have the terminology wrong. its been a while:-) The oil between parts is put under tremendous load or pressure. This is NOT to be confused with oil pressure generated by the oil pump. This is the film of oil between all moving parts. For example, between the crank shaft and crank shaft bearings or between the ring gear and pinion gear teeth. In layman's terms: if the pressure between those parts exceeds the "sheer point" the molecules are in effect broken apart. Think of the molecules as ball bearings. As the pressure increases the balls crush.

Engine: This isn't as much of an issue in (a) naturally aspirated, normally driven and maintained car engine as the pressure generated between moving parts (is) reasonable. Turbo charged, supercharged, towing, racing, etc. anything that increases that pressure and/or adds heat quickly exceeds pressure/heat circumstances normal mineral based oil can endure. This doesn't mean that mineral based oils are as good as synthetics under normal circumstances, because synthetic oils are STILL "slipperier" and still "cling" better then their mineral counterparts. Synthetics are still a better lubricant.

I pointed out engine above for a specific reason. Pressure exerted between drive train parts is MUCH, MUCH, MUCH higher then pressures seen in a naturally aspirated, normally driven, unmodified street engine. For one thing, the area is much smaller in most cases. The area (pressure) between a ring gear tooth and its corresponding pinion gear tooth is incredible! GRANTED, under normal driving conditions, not for as LONG a period of time as in an engine. In an engine its more continuous but less pressure. The problem is, in a drive train, the shock load applied every time you step on the gas and every time you shift and every time you let off the gas, etc. is extremely high. AND that pressure creates enormous amounts of heat. Heat is generated when the fluid is compressed between the two objects (ring and pinion gear teeth for example). Heat that you ALSO can't get rid of real efficiently. No radiator, and relatively small amount of fluid. BTW, this is an argument for aluminum fined - heat sink - style differential covers and automatic transmission sumps that increase capacity. A MAJOR argument can be made for use of synthetic lubricants in any drive train component.

One more thing. Last one, I swear!:-) Synthetics stand up to contamination MUCH better then mineral based lubricants. Don't believe me? Try washing synthetics off your hands. Contamination by fuel, detergents, particulate matter (ie. carbon) and water. All combustion engines are contaminated with water the first time you start one up and shut it off. As the air inside cools moisture condenses inside the engine contaminating engine oil, transmission fluid, differential lubricants, etc. Obviously, the more humid the climate the worse the contamination.

On the side, for the off road'rs in the bunch. Getting water into the crankcase, differentials, transmission or t-case with synthetic is much less damaging to components with synthetic oil then mineral based oils. Any water in mineral based oil immediately breaks down the oil and its lubricating ability is gone. Synthetics do not break down when mixed with water so the lubricating ability is only decreased. That DOES NOT mean that you can just keep running along indefinitely! It means that in emergency situations where you HAVE NO CHOICE but to continue driving the likelihood of doing mechanical damage in the short term is less.

- La Fin