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View Full Version : motor oils (synthetic vs....natural ?)


The Flying Dutchman
06-01-2002, 12:13 AM
1. What is the difference between synthetic vs regular motor oil
2. Is synthetic worth the triple price it sells for around here.
3. What is viscosity breakdown ? I know what viscosity means, but I have never changed the oil to find a loss of viscosity that wasn't a result of higher temperature.

crypto
06-01-2002, 12:34 AM
Apologies in advance... I don't answer all of your answers.

I have a car that came with synthetic oil, and sure enough the owners manual says that it only needs an oil change every 15K miles. Hard to believe, but the extended warranty is very specific, and if you don't follow the schedule, they could void the warranty.

Anyhow, it is generally accepted that synthetic is worth the price, since it doesn't break down nearly as quickly as regular motor oil, but I don't have a cite for this other than a number of mechanics who told me what they thought.

Who knows? It could be a great marketing message that's out there now. I have also heard that if you change your oil and replace it with synthetic, you have to stick with synthetic. I have no idea why.

What's more interesting is the 3K oil change. It's pretty much drummed into your head that you need one every 3K miles. However, this is a relatively recent invention. I had a late 60's muscle car once, and the owner's manual said that oil needed to be changed every 6K miles and the filter every 12K.

This car had an engine (and power) that I've never had since, so I'd think that the oil would break down quicker.... but what do I know? I also have a neighbor that claims that he NEVER changes his oil. He changes his filter every 6K miles, and adds a quart of oil. I guess that could work, but I wouldn't try it.

crypto
06-01-2002, 12:36 AM
Um, I don't answer all of your QUESTIONS.

I need some sleep.

Enola Straight
06-01-2002, 02:30 AM
Regular oil is distilled from petroleum (crude oil).
Synthetic oil is made from esters, a product made from the reaction of an alcohol with an acid.
These esters are purpose-synthesized for the specific loads encountered by heat and friction.

honkytonkwillie
06-01-2002, 03:15 AM
Re: viscosity breakdown.

Butylenes are rubber-like chemical components that are added to motor oil to alter the viscosity. They provide the curious property of increasing the oil's viscosity as the oil temperature rises.

Over time, these compounds break down and the oil loses it's ability to remain viscous enough at operating temperature.

dead0man
06-01-2002, 05:54 AM
1. What Enola Straight said.
2. Depends, but probably not. New, high performance car or fancy aftermarket motor, yeah it might help your engine. Use it if your manual says so. Older cars with old seals that allready leaks a little oil, synthetic could be really REALLY bad for you.
3. What honkytonkwillie said.
dead0man

Gary T
06-01-2002, 02:44 PM
Unless a car came with sythetic oil from the factory, I'd wait till it hit 10-15,000 miles before switching to synthetic, to ensure proper engine break-in.

The oil change schedule Max mentioned was almost certainly for "regular service." The great majority of cars are driven under "severe service" conditions--short trips, stop-and-go traffic, extended idling, etc.--and should have the more frequent changes, nowadays in the 3-5,000 mile range.

Just changing the filter and adding a quart is a recipe for disater. The filter is designed to trap particles. Changing the oil is intended to get rid of corrosive compounds which build up in it, and to replenish oil which has broken down. In a sense, an oil change is more for getting rid of the nasty stuff that's in there than for adding fresh stuff.

I'm not quite sure what this means: ...I have never changed the oil to find a loss of viscosity that wasn't a result of higher temperature. Viscosity breakdown is something that would require testing to determine. It's the viscosity at higher temperatures that would be the main concern. I don't know how one would know whether the breakdown was a result of high temperatures.

Mixing a quart of synthetic with 3 or 4 quarts of regular motor oil is recommended as a cost efficient way to get some of synthetic's benefits. There are some oils that are pre-blended this way.

Gary T
06-01-2002, 02:51 PM
Unless a car came with sythetic oil from the factory, I'd wait till it hit 10-15,000 miles before switching to synthetic, to ensure proper engine break-in.

The oil change schedule Max mentioned was almost certainly for "regular service." The great majority of cars are driven under "severe service" conditions--short trips, stop-and-go traffic, extended idling, etc.--and should have the more frequent changes, nowadays in the 3-5,000 mile range.

Just changing the filter and adding a quart is a recipe for disater. The filter is designed to trap particles. Changing the oil is intended to get rid of corrosive compounds which build up in it, and to replenish oil which has broken down. In a sense, an oil change is more for getting rid of the nasty stuff that's in there than for adding fresh stuff.

I'm not quite sure what this means: ...I have never changed the oil to find a loss of viscosity that wasn't a result of higher temperature. Viscosity breakdown is something that would require testing to determine. It's the viscosity at higher temperatures that would be the main concern. I don't know how one would know whether the breakdown was a result of high temperatures.

Mixing a quart of synthetic with 3 or 4 quarts of regular motor oil is recommended as a cost efficient way to get some of synthetic's benefits. There are some oils that are pre-blended this way.