# Engine Oil Ratings....



## ericp (Feb 23, 2003)

Can anyone explain engine oil ratings to me.

I thought I had a handle on it... Two numbers..First number is viscosity when cold, second number viscosity when warm..

Easy so far.....

The handbook for my Jeep says use a 5-30 oil

Which I take to mean that the oil should be thinner when cold...

...I spoke to the Main dealer and he says, oh no...We use a 15-50 oil its better...

How is using a thicker oil better ?

Why is synthetic better than ordinary (fossil oil) ?

Should I go with the book or the service dept ?

Does it make that much difference ?

Cheers.


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## Griff (Feb 23, 2003)

VISCOSITY

Viscosity is the measure of how thick an oil is. Viscosity, or weight, is another criteria for judging an oil's service rating. Simply put, viscosity is the oil's resistance to flow or motion. Viscosity varies under different temperatures and is vital for maintaining a lubricant film between moving parts. Viscosity plays a role in an engine's cold-cranking ability, the movement of gears, meeting load capacities, heat-up of critical engine parts and the oil consumption rate.

Since the 1960's, multi-viscosity oils have been popular. In simple terms, a multi-viscosity oil, such as 10W-40, means that the oil will pour and flow like a 10-weight oil at very low temperatures yet offer the same lubrication ability as 40-weight oil when the engine reaches operating temperatures.

An oil with too low a viscosity can shear and loose film strength at high temperatures. An oil with too high a viscosity may not pump to the proper parts at low temperatures and the film may tear at high rpm.

WEIGHTS

The weights given on oils are arbitrary numbers assigned by the S.A.E. (Society of Automotive Engineers). These numbers correspond to "real" viscosity, as measured by several accepted techniques. These measurements are taken at specific temperatures. Oils that fall into a certain range are designated 5, 10, 20, 30, 40, 50 by the S.A.E. The W means the oil meets specifications for viscosity at 0 F and is therefore suitable for Winter use.

MULTI-VISCOSITY OILS

Multi viscosity oils have polymers added to a light base (5W, 10W, 20W), which prevent the oil from thinning as much as it warms up. At cold temperatures the polymers are coiled up and allow the oil to flow as their low numbers indicate. As the oil warms up, the polymers begin to unwind into long chains that prevent the oil from thinning as much as it normally would. The result is that at 100 degrees C, the oil has thinned only as much as the higher viscosity number indicates. Another way of looking at multi-vis oils is to think of a 20W-50 as a 20 weight oil that will not thin more than a 50 weight would when hot.

Multi-viscosity oils are one of the great improvements in oils, but they should be chosen wisely. Always use a multi-grade with the narrowest span of viscosity that is appropriate for the temperatures you are going to encounter. In the winter, base your decision on the lowest temperature you will encounter; in the summer, the highest temperature you expect.

10W-40 and 5W-30 require a lot of polymers (synthetics excluded) to achieve that range. The polymers can shear and burn, forming deposits that can cause ring sticking and other problems. This has caused problems in diesel engines, but fewer polymers are better for all engines. The wide viscosity range oils, in general, are more prone to viscosity and thermal breakdown due to the high polymer content. It is the oil that lubricates, not the additives. Oils that can do their job with the fewest additives are the best. Follow your manufacturer's recommendations as to which weights are appropriate for your vehicle.

VISCOSITY INDEX

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.

SYNTHETIC OIL

Synthetic oils are developed in the laboratory- from man made orgainc esters and other synthesized hydrocarbons to provide the exact characteristics desired. These "designer" oils include no impurities, at least when poured from the can. Impurities, of course, can appear during combustion.

Synthetic oil is more expensive because it has to be manufactured rather than just separated from a crude cut.

It can be run for longer periods of time between oil changes because it has better thermal stability. The Mobil 1 commercials where they put dino oil and synthetic oil in pans and cook them until the dino oil breaks down are not hype.

So should you run longer intervals with synthetic oil? Well, there are still going to be acids and other combustion products in the sump over time. These are not removed by a filter. And even the stuff that is removed by the filter will eventually load the filter to the point that its efficiency drops and can go into a bypass mode and stop filtering. Synthetics should still be changed at reasonable intervals unless you use oil analysis.

ADVANTAGES OF SYNTHETIC OIL

Better lubrication properties. Longer intervals between oil changes are possible because synthetics suffer less breakdown due to the better base stock used. Usually the synthetics will have a better additive package, allowing the oil to clean better , pump better at lower temperatures, get to critical areas faster among other things


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## jasonm (Nov 22, 2003)

If your oil is too 'runny' it will 'run off' all the internals faster when the car isnt being used and may cause premeture engine wear in the first few crucial seconds/mins upon start up....


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## Fred (Feb 23, 2003)

Griff, thats one hell of an answer,and good info, fred.

eric, Synthetyic oil is no good for older engines, its to thin, the oil pump in older cars will not pump the thin synthetic as good as the thicker oils, Modern engines are made to better tolerance's, so need a thiner oil, i would stick with the hand book,you have come back if its wrong, fred.


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## pg tips (May 16, 2003)

I agree with Fred, use what the book says. A lot of garages, dealers included, buy oil in bulk and put the same stuff in all cars regardless.


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## Fred (Feb 23, 2003)

Hi, just an aside to the topic, in the last twenty years i have used W20-50 engine oil and semi-synthetic oil in all the bikes i have had [7], two being bought new, BMW,K100 LT, and the Triumph Daytona, all having Slick 50 added, never had any trouble with the engine ,clutch or gearbox, if you read what the so called experts say using Slick 50 will make the clutch slip, [no it does not] using any Car engine oil in a motorbike will balls the bike engine up, [no it does not] there is a lot of tosh talked about oil, some from people who should know better, there used to be a chap in the Sheffield area who would make you oil up, all he needed was the spec number of the oil you wanted and he would make [mix together] different ingredients and sell it five galls a time, a couple of people i worked with used to buy from him. fred.


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## pg tips (May 16, 2003)

to a certain extent oil is oil is oil. It all does the same job some is thicker than others that's all.

I remember my grandad had a 10 gallon drum of Duckhams that he used on everything. His garage had that wonderful smell of Duckhams ground in the dirt on the brick floor!

In the UK our weather is so middle of the road most engines will be perfectly happy on a good multigrade, I use a 15 - 40. Extremes of temperature need different oils of course.

Engines with Hydraulic valve lifters (tappets) tend to work better with the thinner stuff like 5 - 30 or 10 - 40. If I had a pound for every CVH escort I've been to with a tappet banging away because the oil hadn't been changed for years and the auto lifters wern't extending properly I'd be as rich as Roy!









Modern High performance engines tend to be best off with synthetic. As a general rule if it had synthetic out of the factory then keep it on it if it didn't then don't swap to it.


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## Stan (Aug 7, 2003)

I reckon changing engine oil when it needs it is more relevant than the viscosity, as long as you use a quality product.

There are so many under-serviced engines about it defies belief.









Manufacturer's are far too optimistic with service schedules IMHO. After all, if an engine is buggered after the warranty period why should they care?

Change lubricants more often than you think they need to be and you should be safe, IMHO.


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## pg tips (May 16, 2003)

couldn't agree more Stan.

See far too many cars which haven't been serviced in years and the owners rely on guys like me to bail them out of the crap when the breakdown.









Emergency Breakdown organisations are not a substitute for proper servicing!


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## ericp (Feb 23, 2003)

Gents,

Thanks for all the advice....

Its an interesting topic...

I have really grown to love my Jeep and enjoy working on it myself.

The dealer wanted silly money for a service, so I looked at what needed doing and decided I could do it myself. Having invested in a drip tray, grease gun etc. I set about this last weekend...

Was very rewarding and despite the investment in some equipment still cheaper than sending the Jeep to my local Chrysler shop....

However having read all the advice I think I now need to drain the Mobil 1 15W 50 and replace it with 5 w 30.

Cheers


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## DavidH (Feb 24, 2003)

> However having read all the advice I think I now need to drain the Mobil 1 15W 50 and










What! I love that stuff. No such thing as a cold start, lasts 20K ,comes out dead easy and you get a nice sticker for your back window.

Maybe not in a new engine though as it will arrest engine wear and the piston rings/bores wont run in properly.

I put 150K on a company van (and you know how they are cherished







)using the above regime and never had to top up the oil, so it works for me.

BTW I suck the oil out the dipstick pipe, it saves laying underneath and fighting with that stupid cover!


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## Garry (Feb 25, 2003)

DavidH said:


> BTW I suck the oil out the dipstick pipe, it saves laying underneath and fighting with that stupid cover!


 Doesn't it leave a really **** taste though......


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## DavidH (Feb 24, 2003)

....forgot, just gargle with WD40


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## Garry (Feb 25, 2003)

Thats what I do, works every time........


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## Stan (Aug 7, 2003)

WD40 is good for watches too.









I'll duck, just in case the "boss" is watching.


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## ericp (Feb 23, 2003)

I seem to recall reading a letter from a chap in a motorcycle magazine once...

He advocated WD40 instead of chain lube for motorcycle chains...







)


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## Garry (Feb 25, 2003)

ericp said:


> I seem to recall reading a letter from a chap in a motorcycle magazine once...
> 
> He advocated WD40 instead of chain lube for motorcycle chains...
> 
> ...


 The bloke must be a plum Eric.......


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## Garry (Feb 25, 2003)

......Anyway,

What do you think of your B2, I'm tempted with the white dialled one?


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## ericp (Feb 23, 2003)

I have the white / creamy dialled B-2....

Mr. Crowley was very taken with it when we met recently.

Its a nice solid watch, outstanding timekeeping, engineering on the geared bezel is superb....

I can send some pics if you like.


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## DavidH (Feb 24, 2003)

..or post it up or put it into the photo gallery.


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## Garry (Feb 25, 2003)

ericp said:


> I can send some pics if you like.


 Thanks Eric,

I've handled one a few months back and it seemed superb, I just wanted some reassurance from Breitling fans here that they are worth the money......


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## bry1975 (Feb 6, 2004)

You do know what the WD stands for in WD40









Basically it took the inventor 40 attempts to perfect it.

WD40 = Water Displacement 40th attempt.


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## Garry (Feb 25, 2003)

Thanks for that bry, it's been bugging me for years........


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## pg tips (May 16, 2003)

we use "duck oil" at work but I bet it's not really oil obtained from ducks!


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## rhaythorne (Jan 12, 2004)

So Duckhams isn't made from duck's legs then?


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## ericp (Feb 23, 2003)

WD 40 is fantastic stuff.

The winch on my Jeep has been completely submerged in deep water and the solenoids and electric pack (liberally coated in wd40) still worked a treat.

Marvellous (and very usefull)


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## Stan (Aug 7, 2003)

WD40 is the best maintenance spray available, imho.

My dad was one of the first retailers of WD40 in the UK back in the early 1960's.

It cost something like 10 bob for a small can back then, we treated it like liquid gold.









There was nothing like it available then and nothing quite comes up to its standards now, imho.

I have a forty year relationship with WD40, boy that's sad.


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