Engine What kind of oil ?

reynoldston said:

The part I don't understand is why would you want 10W30 over 10W40. Do you mow grass in Scotland when it is real cold and need the lighter oil? The 10 is when the mower is first started and the oil is cold and the high number 30 and 40 after everything is up to operating temperature.

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Practically every walk behind push mower I have owned says "do not use 10W40 oil" in their manuals.

My push mowers are over 30 years old and never had a owners manual because I bought them used and I never read a owner manual for a walk behind mower. I have always used SAE30 in them. They also get very few hours of running seeing I just use them for trim mowing. I still wonder why not the 10W40, is that too heavy of a oil and what is it going to harm? Bearings, cylinder walls, crankshaft bearings? The only time I have ever seen a problem with oil in any small engine repair job I have worked on was they ran it out of oil. Also if I bought a new push mower and the owner manual said not to use 10W40 I would NOT because they built it and know more then I do about that mower. What are we talking about less then one quart of oil for a years running so why not use the best and proper oil. I know that the newer transmissions use a lot lighter oils because they use a lot of needle bearings and the lighter oil lubes the needle bearings better and also for better gas mileage. Back in the early 30's they used a 140 weight in gear cases and I think they did that because of poor design seals and they didn't leak as bad. Times and lubrications is changing for the better.

I would guess that the reason for not wanting 10w40 is because the small engines are not pressure lubricated. The viscosity may be a bit heavy, I believe they rely on gravity etc.

My mower's manual calls for SAE 30W. I used to buy the 48 oz. jug of B&S mower oil. Then I figured, wait, other manufactures must make SAE 30 detergent based oil. Last month, I got 5 quarts of Peak SAE 30 detergent oil and an auto oil filter for $10, so that should last me a while.

A multi-viscosity oil has additives (amazingly called viscosity index improvers) to make it multi-viscosity. Obviously these additives are not oil, so they displace actual oil. Back in the middle 80's GM has a rash of camshaft failures and they blamed it on oil with too much additive and not enough oil, to the point of denying warranty if 10W-40 oil was used. Also, I work with diesel engines where multi-viscosity oil is not allowed, one reason being that when the additives break down, the oil acts like the thinner base stock, even at temperature. Being as how out little air cooled motors probably run pretty hot, this could be a reason for the no 10W-40. I have an older B&S that wants single weight; 30 if its above 40 degrees and 10 if it's below.

Thank's for the history lesson. That's what I like about this site we are always learning.

Grass ala Mowed said:

A multi-viscosity oil has additives (amazingly called viscosity index improvers) to make it multi-viscosity. Obviously these additives are not oil, so they displace actual oil. Back in the middle 80's GM has a rash of camshaft failures and they blamed it on oil with too much additive and not enough oil, to the point of denying warranty if 10W-40 oil was used. Also, I work with diesel engines where multi-viscosity oil is not allowed, one reason being that when the additives break down, the oil acts like the thinner base stock, even at temperature. Being as how out little air cooled motors probably run pretty hot, this could be a reason for the no 10W-40. I have an older B&S that wants single weight; 30 if its above 40 degrees and 10 if it's below.

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You have it backasswards
conventional oil in 10w-40 is a 40 weight and the additives make it like a 10 when cold that is why as it gets mileage on it and the add-pack is depleted it get thicker.

Now with a synthetic it is the other way around it is made from 10w and the additives make it a 40 when hot.

Whatever. Copied right from the Castrol Oil website:

"A monograde is an oil whose viscosity is defined at only one temperature, either high or low. A multigrade must meet both high and low temperature viscosity requirements simultaneously. This makes multigrades an easy and popular year-round choice for drivers who experience hot summers and harsh winters. They are easily recognized by the dual viscosity designation (i.e. 10W-30 where the 10W is the low temperature, or winter designation and the 30 is the high temperature designation). It is the viscosity modifier additive that produces a thickening effect at high temperatures but is dormant at low temperatures. "

You're thinking of a "pour point depressant."

There was a problem with early multivis oils , when too large a gap was bridged, 10 to 40.... Using mineral oils... There never was a problem doing that with synthetics ....
the chemistry has been worked out now for more than 20 years, you will not have a problem with large range viscosity oils... . But like anything it will likely remain as folk lore for 50 years, or until most of those that have heard the problems from 70's & 80's are no longer around, or when enough people look into the chemistry side of lubes...
Detergent oils came about in the 30's and 40's... I still hear the most remarkable things that people repeat about using non detergent oil in an engine... it is amazing how bad information continues even after more than 70 years...
Multi vis is not just a good idea ... synthetic is not just a great idea... but it will take time for some to figure out why... :smile:KennyV

KennyV said:

There was a problem with early multivis oils , when too large a gap was bridged, 10 to 40.... Using mineral oils... There never was a problem doing that with synthetics ....
the chemistry has been worked out now for more than 20 years, you will not have a problem with large range viscosity oils... . But like anything it will likely remain as folk lore for 50 years, or until most of those that have heard the problems from 70's & 80's are no longer around, or when enough people look into the chemistry side of lubes...
Detergent oils came about in the 30's and 40's... I still hear the most remarkable things that people repeat about using non detergent oil in an engine... it is amazing how bad information continues even after more than 70 years...
Multi vis is not just a good idea ... synthetic is not just a great idea... but it will take time for some to figure out why... :smile:KennyV

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Kenny you are so right on this their is nothing so misunderstood as motor oil.

I have used multi-grade in all my mowers since it first came out about 60 years ago, I'm still waiting for them to blow up.:biggrin:

Grass ala Mowed You should spend a few months reading UOA on Bobs the Oil Guy Forum you will find it time well spent if you want to learn more about oil.

Also for all those who don't understand multi-grade oil or if you think it is not better for your engine I recommend you read this link.







Motor Oil Viscosity Grades Explained in Layman's Terms