Oil Viscosity--Food for Thought or Fuel for a Flame War?

[rScotty]

Sounds like a lot of folks have swallowed an oil specification manual - and then interpreted it in in different ways.

I wonder if someon could what it is about the chemistry of multiweight oils that makes them change viscosity with temperature differently than single weight oils do.

 

[MAX-24-Dean]

Back when I had a mechanical shop you wouldn't believe the range type of oil in cars, trucks, tractors, and bikes that people brought in. Many times we saw vehicles with oil that hadn't been changed in 20 years or longer. It wasn't unusual to have upwards to half an inch of dirt and metal sludge in engine oil pans. I've seen old oily sludge so thick that the oil pan wouldn't drain. We would drive a punch through the goo to get the oil to drain, drop the pan, and clean the sludge out with paint scrapers.

Again and again we saw complete engine and running gear failures due to not having any oil at all in the engine, tranny, rear end, axles...etc.... . BUT,
I NEVER ONCE SAW A FAILURE THAT I COULD SAY FOR SURE WAS DUE TO BAD OIL or OLD OIL - or even to cheap oil.
Not once. No matter how bad or old it was or how hard it had been run or how burnt it smelled. I didn't even see the expected wear.

In spite of that, I put the best premium oil in my machines and always have. I haven't had any oil related problems either....but my experience makes me wonder.

rScotty

Good post.

Had an International H we used to load hay with and pull and irrigation pipe cart. We added a quart of oil everyday as that is approxiamtely what it burned. Never changed the oil (changed filter twice per year) until one year the farm mechanic said it was probably time to scrape the goo out of the oil pan. As a teenager at the time it was quite an education, there was more than a 1/4" of multi colered sludge in the bottom of the oil pan. I was told it was the first complete oil change on this tractor in 13 years.

 

[Milo]

Multi weight oils include viscosity improvers. Viscosity improvers were explained to me in layman terms by a chemist with Spectro Oils as 10w oil is syrupy when cold and very, very, thin at temperature. 10w-40 oil is syrupy when cold and thin at operating temperature because it has VI polymers added. Polymer additives expand with heat to reduce the oil's thinning. Have you ever cut the cover off a golf ball? Think of the thin rubber banding tightly wrapped around a small solid ball as the VI when cold, and a plate of cooked spaghetti on a plate as the same VI when it becomes hot. But they do gradually break down.
It may have somehow changed with synthetics but in the past multi viscosity oils always started life as the low number; 10w-40 is 10w oil with VI added to make it behave like 40w when hot. As the VI's wear out the oil slowly reverts to its base weight even when hot. So the 10w-40 oil you put in your car may test more similar to 10w-32 after 3,500 miles, or 10w-25 after 6,000 miles.
10w-30 has less VI than 10w-40 therefore looses less percentage-wise because less VI to wear out. My Moto Guzzi specs 10W-60 synthetic oil, that's a lot of VI or whatever synthetic trickery it requires.

 

[rScotty]

Good post.

Had an International H we used to load hay with and pull and irrigation pipe cart. We added a quart of oil everyday as that is approxiamtely what it burned. Never changed the oil (changed filter twice per year) until one year the farm mechanic said it was probably time to scrape the goo out of the oil pan. As a teenager at the time it was quite an education, there was more than a 1/4" of multi colered sludge in the bottom of the oil pan. I was told it was the first complete oil change on this tractor in 13 years.

And I'm guessing it was a good education for a teenager and didn't make a bit of difference to the tractor.
But it didn't hurt, either. Maybe sludge makes a pretty good filter.
Sludge as a filter and particle trap is used a lot in water treatment plants.
rScotty.

 

[California]

.... . BUT,
I NEVER ONCE SAW A FAILURE THAT I COULD SAY FOR SURE WAS DUE TO BAD OIL or OLD OIL - or even to cheap oil.
Not once. No matter how bad or old it was or how hard it had been run or how burnt it smelled. I didn't even see the expected wear.

In spite of that, I put the best premium oil in my machines and always have. I haven't had any oil related problems either....but my experience makes me wonder.

Re oil change intervals: The oil companies would like to define all driving as 'severe use' needing frequent changes but that seems to me to be a waste of money, time, and natural resources.

When I was young and poor, well, also older and cheap , we've generally had one car in excellent condition and then a second one bought cheap where we were clearly going to be its final owner. Best example was an old early Taurus wagon, the one that seated 3-3-2, for Older Daughter when she got her license at 16 and would be hauling friends around. (Also anticipating the chance of dents, but she never did). It looked nice but near 100k miles when we bought it. Oil change interval for that Taurus was after it had needed two quarts of top-up oil then was down again - so over 10k miles between visits to JiffyLube. We retired that one when its torque converter started grinding at 130k miles, which I've read was expected for those. It was a good first car for a kid. Cheap to buy, operate, and minimal depreciation cost over the years we owned it. Extended oil change intervals didn't seem to hurt it.

Likewise the 99 Subaru Outback we bought new. It's always needed a quart after about 5k miles, since new. Oil change interval is when it needs a second top-up quart. That car is semi-retired now, used for occasional ski trips or pulling the 4x8 trailer in harvest season, so it can be 2.5 years before an oil change. At 140k miles, fuel economy and oil use hasn't changed since new.

The 2005 Focus Wagon has never used oil since new. My usual waiting for a car to need a quart before thinking about an oil change, isn't applicable. I see the same engine in Europe calls for 10k oil change intervals but this one isn't down much at 10k. Nearly all its miles are the 100 miles between home and ranch so I don't think it stresses the oil like a car used for short trips around town. 10~12k mile oil change intervals hasn't caused problems.

In summary - I think modern oils are far better now and its reasonable to use the longest oil change interval found for any version of a specific engine. Also cheap (JiffyLube etc) oil of any major brand seems to be sufficient. Cars aren't like semis or tractors that run hard their entire life.

 

[uphere]

I remember I had a 1966 Pontiac with a 283ci. I had to run 20W50 in the later years because it burnt a bit - by then it didn't owe me anything. One winter I was away on work and my Dad had to move it - it wouldn't turn over. He checked everything and finally gave up. He called me up north to get some ideas - I said if you can, get underneath with a blow torch and heat the pan up real good - he did - it eventually started. He moved it - and that winter it didn't move again.
I also had an old Kawasaki Bayou (1987 I think) ... it was well past its due date when the rear seals started to leak about a decade ago. Not wanting to put any money into it, I filled it with STP (the thickest stuff I could find on hand at the time) - I still have it on the farm - it still works - and no leaks!

 

[RalphVa]

For high temperature operating protection and thermal breakdown, the second number in the SAE grade is what is important ( i.e. 15W40). For easy cold weather starting and initial lubrication, the first number is the import one (i.e. 15W40). In really cold weather 5W40 would be acceptable in an engine that calls for 15W40.

5w or 0w40 is acceptable in ALL weather.

 

[RalphVa]

Sounds like a lot of folks have swallowed an oil specification manual - and then interpreted it in in different ways.

I wonder if someon could what it is about the chemistry of multiweight oils that makes them change viscosity with temperature differently than single weight oils do.

It's called Viscosity Index. The higher the VI, the less change with temperature. The farther apart the xx and yy #s are in the xxwyy oil spec, the higher its VI will be.

Typically dino oils with about 20% or so of additives to raise their VI and lower their pour points are about 140 VI.

Synthetic oils are typically up around 200 VI.

Synthetic oils are like long chain paraffins, typically about C20 or so, with a few side chains. The side chains keep them from solidifying at room temperature like a wax does. Wax is one thing that has to be removed from a dino or some co-called synthetics made from high pressure hydrotreating. Synthetic oils typically have NO bad actor chemicals even in ppm levels to affect how long they can be left in service. They just have to put up with blowby chemicals in the combustion engines.

Dino oils are made up of a smear of different chemicals: long chain hydrocarbon, some cyclic hydrocarbons, etc. They also have ppm levels of aromatics and other bad stuff that affect how long they can be left in service with chemical reactions doing bad things to them. Blowby chemicals will react with those ppm levels of bad stuff.

I worked as a chemical engineer for 31 years in the lube oil industry. That's why I know this stuff. Just unsure how to spell it out to those who do not know.

 

[Williy]

Father in law purchased a 1976 chevy 1/2 ton pickup
every time he got gas he had to add a quart of oil.

Another guy I knew had a Studebaker station wagon he always
carried 5 5 gal pails of drain oil as he burned more oil than
gas. If we had to stop for a stop sign the whole area was
engulfed in smoke and we would take off because nobody
would move until the cloud cleared the area.

willy

 

[California]

Another guy I knew had a Studebaker station wagon he always
carried 5 5 gal pails of drain oil as he burned more oil than
gas. If we had to stop for a stop sign the whole area was
engulfed in smoke and we would take off because nobody
would move until the cloud cleared the area.

That brought back memories. When I was a little kid in the 50's a friend's father had an 'Americar' woodie station wagon. Just an old car then, not a collectible. I think related to Willys or maybe Studebaker. It had so much stinky blowby that it was immediately sickening, unbearable, to ride in the back seat even for just a ride home from school.

That father later went blind, then died of cancer. I'm sure because of that car.