Oil Viscosities and Weights

Very comprehensive. Thanks for these posts!

Great links. I can often find things to whine about, but could find nothing in these articles to argue with.

Nowadays the "30" end of the spec (indicating oil viscosity at operating temp) is very consistent -- so at operating temperatures the two grades are the same viscosity. During startup however, the 5w-30 flows better, and getting oil circulating quickly at that time is a good thing.

Go with the manufacturer's recommendation. There are still plenty of mechanics who think that thicker oil protects better. It doesn't.

Hello Ken

There are still plenty of mechanics who think that thicker oil protects better. It doesn't.

I resemble that remark, they say fools rush in, I guess is as good as places any to rush into an argument with no right answer.

The owners manual for my Dodge recommends 5w-20 exclusively under any operating conditions. The problem I have with this is not the low viscosity but rather the single range recommendation for any conditions. Anybody that believes that 20 weight oil will have the same viscosity (using this as a poor point) on a 0° winter morning idling around town as it will towing a trailer at 70 miles an hour on a 120° summer day has been smoking 4-20.

The first time I ran 20w-50 in a engine with about 2 1/2 thousand rod and main bearing clearance I was rather amazed. Idle oil pressure started at about 40 psi, increase to about 80 psi (typical pressure cold idle with 50 weight) as the engine warmed up, then dropped back down to about 40 psi at operating temperature.

To the point, oil temperature directly affects viscosity (by definition) the lower the viscosity the more likely the oil film is to break down and allow metal to metal contact. By no means is this to say that 50 weight oil would provide better low temperature protection than 5w20 in a engine designed for 5w-20, the engine probably wouldn't last very long using 50 weight.

I have no doubt that thinner oils provide better fuel economy, I do question how much engine life is being sacrificed for minimal gains in fuel economy. Every vehicle I've ever owned (until this one) including a relatively new motorcycle makes allowances for operating conditions, and ambient temperatures. To me multi viscosity oils entire purpose is to normalize their thickness over the highest practical temperature range.

To my understanding there is been some problems with the 10W40 oils caused by its 30 viscosity point range, at one time 15W40 was considered to be the best compromise available, for some reason 20 W-50 does not seem to be plagued by the same problem. I can't quite understand why 5w-30 would not be a better choice for any engine than 5w-20, that is at least for summer operation.

Perhaps someone can explain the error in my logic. Several times in my life I've heard about the new and improved multi viscosity oil's, I've always adopted a wait-and-see attitude.

Sometime in the 1980s multi-viscosity oils were approved for aircraft engines. I kept using my behind the times 50 weight Aero shell in my 182 and stayed with my wait and see attitude, and I did see, aircraft falling from the sky with engine failures.

I wish I could wait-and-see how the new hot tip 5w20 is going to relate to engine wear. With the multi-displacement system I'm semi-stuck to 5W20, or at least until I find out whether the engine management system compensates for oil temperature when bleeding off the lifters.

PS here's a link to throw a little more oil fuel on the fire
http://mcgeerf.tripod.com/americansyntheticoil/id17.html

It contains some pretty good information, and some test on various oils. You just need to remember it is published by Amsoil

(using this as a poor point: I don't know what I was thinking the poor point is obviously completely different than viscosity ,at least in a way I was using it.

http://en.wikipedia.org/wiki/Motor_oil

"In layman's terms, the viscosity of a liquid can be thought of as its "thickness" or a quantity of resistance to flow. The viscosity must be high enough to maintain a satisfactory lubricating film, but low enough that the oil can flow around the engine parts satisfactorily to keep them well coated under all conditions."

I took this from the Encyclopedia. Actually the whole article is worth a read.

Sorry about the misstatement, also noticed a few typos.

Hi YWR,

Oil thins out with temperature logarithmically, so a cold oil (at 0°f for example) even if it is 5W-20, is too thick, far thicker than the oil is at running temperature. According to the Wikipedia article, some hybrids are now using 0W-20 oil (which I didn't know).

The higher the viscosity, the higher the internal friction, leading to more heat, lower mileage, etc. In a relatively new engine, with tight clearances, it is better to have the oil flow efficiently than to provide the sort of "cushioning" required to quiet a worn engine. Tests show that engines wear less (rather than more) with thinner oils, so you can have your cake and eat it too.

As the wikipedia article says:

Many new vehicles are marked to use 5W-20 oil (Honda, Ford, and more recently Toyota) which is not much thinner than a 30 weight oil. Nay-sayers of 20 weight oil's ability to protect engines should note that typically, 30 weight oils shear down into the 20 weight range anyway. Most engine wear is during start-up and warm-up period, where the thinner 20 weight oil's flow is desirable. Overall, lab test results of the wear metals contained in used oil samples show low or lower wear with 20 weight than 30 in applications it is specified for.

For old engines or very worn engines with large clearances, higher viscosity helps reduce noise, and maintain oil pressure. But in a modern engine (designed with the clearances to support it's use) 20 weight is thick enough resist being squashed out of clearances (permitting metal-to-metal contact or only or boundary layer lubrication). Any thicker than "thick enough" just contributes to higher engine temps and reduces lubricity.

Hi Ken: Oil thins out with temperature logarithmically, so a cold oil (at 0°f for example) even if it is 5W-20, is too thick, far thicker than the oil is at running temperature.

The fact that oil thins logarithmically is something I was unaware of. But that also tends to support my point . The initial low viscosity does concern me however I must admit to being a relic. What really bothers me is restricting the upper viscosity number no matter what the ambient temperature is, or vehicle load.

The first thing I did after I purchased my new truck and saw that manufacture recommended 5w20 for any conditions was to do some online research, it took a little while on Google to find the original articles I read, while looking I ran across a excellent link explaining viscosity . I thought some might be interested in checking out this link.

"Viscosity Index is an empirical number indicating the rate of change in viscosity of an oil within a given temperature range. Higher numbers indicate a low change, lower numbers indicate a relatively large change. The higher the number the better. This is one major property of an oil that keeps your bearings happy. These numbers can only be compared within a viscosity range. It is not an indication of how well the oil resists thermal breakdown."

I'm not sure about the credentials of the person I'm quoting here, his article is fairly comprehensive. At this hour I'll take anybody that agrees with me.

http://www.240sx.org/faq/articles/oil.htm

http://www.noria.com/learning_center/category_article.asp?articleid=294&relatedbookgroup=OilAnalysis (sorry, link no longer available)

I am probably going to substitute synthetic in place of the regular oil and remain with the 5W20 for the time being in the new Dodge. At least until I can find further information on the engine control system. As far as 0W20 a friend of mine told me about this a year or so ago. I believe it was spec for his Volkswagen although I'm not certain. Thank goodness it wasn't specified for the Dodge. Pouring zero weight oil into an engine would send me into therapy........ again. Signed the relic

Hi All About M.E.:

Your contribution is really useful. If I could, I would give you a star. Thanks.

The most important thing is to follow the manual. The grade and rating of the oil is clearly spelled out for the conditions in which the vehicle is used as well as the recommended change interval. 5W30 may be the recommended grade, but chances are, there will be a chart showing what grades are suitable for the environment you drive in. If I lived in Minnesota, you can bet the 5W30 would go in my engine. In Maryland, the temperature barely goes below 20 F, so 10W40 works just fine and protects well in the stinkin' hot summer heat. Sometimes I do wonder if the the manufacturer recommends the lighter grade oil to meet CAFE standards at a slight cost in engine life?

I don't know if there is any sacrifice in engine life but the lighter oils are definately specified to improve fuel economy. Sez so right in the links....

The lighter oils get to the parts to be lubricated much quicker, less time "metal to metal"!!

Synthetics also "stick" to parts better overnight and longer, so no "metal to metal".

If you get a metal pot or a sheet of metal and heat it up on a gas ring or similar, put a few drops of mineral oil on one part and a few drops of synthetic on another close by (so they have about the same temperature), watch what happens, the mineral oil burns and leaves a varnish behind, the synthetic eventually evaporates and leaves basically nothing behind (assuming both oils unused and fresh!!)

Varnish is a fact of life with mineral oils that can cause real problems in an engine over long periods. What I don't know is if the later use of synthetic will eventually remove deposits of varnish or not. My guess is that it will either remove it slowly or at least it will not get any worse......but guesswork is not really good enough!!

If your car is still under warranty DO AS THE MANUFACTURER SAYS.

DO NOT under any circumstances do what your mechanic says. If something was to happen to the engine one of the first things that the manufacturer will do is take an oil sample AND if you have not used the recommended oils, your warranty is null and void.

The only time you depart from manufacturers instructions during warranty period is if you have written confirmation to do so.

I agree. I would be interested in learning why the mechanic thinks you should change.

I think that some mechanics think that they know everything and treat most customers as imbeciles, because they do not know anything about their cars.

This was certainly true in the maritime industry. e.g. I was telling a class of students about the requirements of a marine diesel engine lubricating oil. Talking about additives I pointed out that one of the most important additives was the detergent/dispersancy additive............this is why your oil turns black in 50-100 hours. The detergent additive scours the carbon from the engine and the dispersancy additive holds the carbon in suspension.

A student replied "my mechanic puts xyz oil in my engine and its just as clean as the new oil when he does an oil change" I suggested that it would be a good idea to change his mechanic. Probably a not too good an automotive mechanic, that turned himself into an instant marine diesel mechanic...........and knows even less about that.

Just one of many stories I could relate.

I think you should ignore your mechanic as the other writers say, today's modern engines, especially Japanes engines with their tighter bearing, and piston clearances demand the type of oil specified, the oil you might say is engineered for that particular use, it's only when you get up to the 100,000 miles mark, that you might start thinking of the higher viscosities, go into any Halford Store (for us in Britain) there you will see the specs for the high mileage vehicles, they differ remarkably from your new engines, There are also high mileage oils specified for vehicles such as mine, which is a Skoda Octavia 1.9 TDI, the oil in that can be left in for two years they claim, or 20,000 miles, it may cost more, but it cuts out the servicing costs at the garage, but I'm a 6,000 miler, and change my semi synthetic oil and filter at that mileage! it seems to work. In your instance, I would say to the mechanic stick to what the book says, and you can't go wrong, if it does then it's up to the manufacturers to explain why, Your mech. can always deny what he said to you!

I have had 5 TD-I engines, all of which used full Synthetic, for the full mileages specifid. The last two cars had a computer (and longlife III Oil) and the computer required oil changes at around 20,000 miles, in spite of pulling a heavy trailer a lot!!!

My biggest problem with Synthetic is that it takes around 15,000 miles just to run the engine in and mileage and oil consumption are still going down at over 40,000 on my newest car!!!

My experience was that at around 100,000 miles, these engines are at their peak, using almost no oil and giving great MPG.......

A Taxi company I use in Vienna, drives their Skoda Diesel TDI taxis till about 500,000 Kms and sell them in full running order.....2 to 2 1/2 years old!!! They have never had one break down due to high mileage....

We had a Mazda MPV and one day I mistakenly bought 10w-30 instead of 5w-30. Wot the heck, it won't matter sez I and proceeded to change the oil.

Of course the engine immediatly started this nasty valve lifter rattle because the hydraulic adjusters wouldn't fill properly.

So the next day I had to go out and buy 5w-30, drain the 10w-30 and put the lighter oil in.

The rattle stopped immediatly.

I don't know how other makes react to this. The other posters are correct with respect to warrenties and tigher tolerences in general. Specifically to Mazda, in my experience. a heavier oil is the wrong move.

I would stick with what the manufacturer says until your warranty expires. Then I would suggest royal purple motor oil for it .

Heck yeah! Royal Purple for the win! I have an '02 Nissan Altima and I have been running Royal Purple in it for years. Switching from conventional oil to the synthetic made my engine idle much smoother. It's good stuff.

Quite a few synthetic oils are very good, BUT that does not alter the fact that you MUST follow the manufacturers instructions during warranty periods.

e.g. Caterpillar say that their engines can be run with synthetic oils but add that any warranty claims would probably not be honoured.

One extra point has come to be very clear to myself after reading through all the posts in this blog, and it something that I have done anyway as it looked to be a good idea is "to always let an engine start without throttle and run for a few seconds at least before driving off".

Loading up an engine when very cold with high revs (as many seem to like to do) would appear to be quite a bad idea......

Also, years ago when I used to rebuild engines, firstly I rebuilt the engine with a lot of good (then) multi grade squirted over any moving parts and then either I hand turned the engine with and eye on the valve train oil supply (rocker/cam cover off), till oil appeared, it could be easily 40 to 60 slow revolutions with a stiff new engine till I was certain that oil was now available at the top of the engine or I disabled the ignition and used the starter for the same purpose.

Obviously oil available at the top of the engine is not a 100% guarantee that it was at all points where oil was needed, but I never had any problems as a careful blow though of all oil pipes and galleries was also made during the rebuild.

Another point that an old mechanic once told me (only possible if you have built the engine yourself really! And he bored out my blocks for me and supplied the new pistons), once the engine is running properly, ignition set up. Stop engine, then go and empty my bladder, make a sandwich or two and get something non alcoholic to drink and get in the car, start her up and drive at around 30-40 MPH on roads with little or no traffic and put at least 200 miles on the clock in one go without switching off the engine.... a long winded boring job is all I can say......if you have to stop, leave engine ticking over......

But all the engines that I treated in this way proved to be very economical from day one on petrol, used little oil and appeared to be at the high end of the expected power output when compared with similar engines on the road.....in fact a "good engine!"

Mostly they were A or B-series motors from BMC, but I also did this to several Jaguar engines (mostly straight six 3.8 engines) and Hillman Imp engines......all ran better than similar engines for one reason or another........I had people waiting weeks/months for me to do my "special tricks" as of course I did not let on what the special trick was either!!! I was still in the RN at the time and had the use of all their fantastic workshops too!!!

In my young days, I used to be an engine fitter, fitting engines into Royal Navy and foreign navy MTB's and Inshore minesweepers, these invariably had 6 cyl. Foden 2 stroke generators, with my knowledge of running engines in those days, I would always start the generator and idle for a few mins. until one day we had the Foden engineer on board, he had very different ideas! his method was to put the engine on full rack, press the button, and bring it on full load straightaway, his reasoning for this, was the fact, the exhaust would build up with carbon very quickly and affect the performance, and so it was, we followed suit!

I also had an experience with a 10 cyl. Ruston,or Paxman, it's a long time ago! we experienced a knock in the starboard engine, the Makers were contacted, and a service engineer was diverted from a job in Alaska, he was a little cockney chap, his first job was to remove the cyl. head from one cylinder, he found nothing untoward, he did other things, and came to the conclusion it was a characteristic of the engine! after he left, we did some more sea trials, and stripped down the fuel filters as a routine, these were quite big filters, holding approx. a gallon of fuel in the chamber, as I removed the plug there was no fuel in there it was practically all water, the engine had been trying to emulate a steam engine, this was the knock we heard, steam being produced in the cylinder! Motto of this is never believe the service engineer! only joking! She completed the remaining sea trials, and was handed over. I apologise for diverting from the subject.

Depending on the exact type of 2 stroke and the way its lubrication was organized, that may or may not have mattered....some 2 strokes have the oil mixed in the petrol, some have it separate, but still mix it in the petrol, some use a similar system to a car....

I am sure that any small amount of carbon you generated would have been burnt off when on load! He sounds like he was just trying to put you wrong for no reason at all.....

The engines I was talking about were 2 stroke diesels!

...which you forgot to mention as that puts a completely new face on the problem!!! Did you not mention that important point just to put us off balance?

Sorry about that Andy, my right hand sometimes never knows what the brain is thinking, As I recall, the other problem we had with the exhaust was a special flexible 90deg. bend they put into the system straight off the manifold, this was treated in some way as far as I can recall to make it heat resistant, and it was somewhat stiff,the object was not to coke this pipe up, hence the blast as soon as it started, also as I recall the engine was on rubber mounts, this would have been a neccesity on minesweepers, which some of the boats were.

What's this.....................doing "rabbits" in the engineers workshop?????

Not the done thing old chap....................would never happen in an RAN engineers workshop...................ha, ha, ha. The benefit of that was that you had all the equipment and materials that you required.

I mean you had to do something when things were slow..........or when you were duty..............or required on board for duty over the weekend for telling the Senior Engineer to do something it is actually physically impossible to do.

....and you never made a "rabbit"? Who are you trying to kid????

hmmmm.........now that you have jogged my memory I could have made a few, or several.

I don't know how many pairs of "olde" brass cannons and carriages I made..........I never even got a set myself...............something went horribly wrong there.