I don't understand oil wieghts...

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I don't understand oil wieghts...

Postby Chug-A-Lug » Sat Jun 10, 2017 1:55 pm

Hi All,

It's about time I renewed the oil and serviced the engine on my Dexta, having only kept fluids topped up since owning it a few years. My old Operators Handbook says 20w/30 for the engine, gearbox, and back axle. However, there are lots of posts on here advising 20w/50. I don't understand the difference so I can't make an informed decision, can anyone help me understand? Also, if the handbook says the same grade for engine/gearbox/back axle then can I use a universal oil throughout?

Thanks for your thoughts,

Sam
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Re: I don't understand oil wieghts...

Postby shawnee » Sat Jun 10, 2017 5:44 pm

20w50 means it is a blend of 20w to 50w oils, a blend and only a blend :clap: :beer: only a blend, mine works better with straight 30w oil and some lucas oil additive. If I crank it in the winter I use a oil pan heater and the dexta atomizer. When you pour 90w you can see the difference also in pouring 30w or 20w or 10w.;10w30, 15w40, 20w50 is only a blend of those oils whatever :
15w40 is too thin for mine, It has blow by: it is 56 years old and it likes 30w better; no blow by :clap: :clap: until til I rebuild I use 30w, if it gets a rebuild maybe switch 15w40 or may be not , looking mf285 manual specs. recommends a straight weight oil 30w above 90F, looking at my ford 4000 manual states straight weight 30w diesel oil for diesels at above 75F they must know some thing. The only thing a blend does that I see is help starter turn over more easy , I do oil pan heater for that. If needed.
Last edited by shawnee on Sat Jun 10, 2017 9:47 pm, edited 1 time in total.
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Re: I don't understand oil wieghts...

Postby shawnee » Sat Jun 10, 2017 8:57 pm

Just what is the actual SAE weight for 15w40 and 20w50 BLENDS? That I have never heard! Looking at my cat d5 manual it states SAE 30 above 32F not 15w40 or 20w50 blends again why they state straight weight oil and not blends. They must know some thing that we do not.
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Re: I don't understand oil wieghts...

Postby Chug-A-Lug » Sat Jun 10, 2017 11:20 pm

Thanks Shawnee, I'm starting to understand. The handbook states 20 H.D. as equivalent to 20w/30. I still don't know which end of the spectrum is heavier (thicker?), and which is lighter. And the benefits or hazards involved in choosing heavier/lighter oils that specified...
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Re: I don't understand oil wieghts...

Postby shawnee » Sun Jun 11, 2017 1:07 am

What I found in the dexta operating manual is Above 90F 30w in the engine : transmission 30w above 20F, Below 20F 20w in the transmission, no where is or does it show it a blend, shows 20w/30H.D. It does not state blended oil. 15w40 is probably 15 weight oil 20w50 is probably just a 20w oil with additives, my dexta will use a blend like go going to fire. I know probably needs rings it's on the list. I am using 30w in the engine and transmission 90w in the steering box.
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Re: I don't understand oil wieghts...

Postby shawnee » Sun Jun 11, 2017 8:35 pm

The summers over here get over 100F the DEXTA does not like SAE 15W oil; Thats what is on 15w-40 label SAE15w is does not state w by the (40), no wonder; blow by on 56 years old engine. I will just put 30w in it from now on.
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Re: I don't understand oil wieghts...

Postby Brian » Mon Jun 12, 2017 3:53 pm

The main reason 20/30W and others were not quoted in the manuals is that they had not been invented. :cry:

There were some multi grade oil but they did not come into common use until the late 1960's from my memory. I know we had a hard time getting Ford to accept Castrol Multiuse in the Ford Force range then Castrol added brake lubricants for the "Wet" brakes and we had to go back to "straight" oils like HDD 20 in the engines because, under light use, the additive plated the walls of the bores and caused blowby. That is why I would not recommend oils like Castrol MP in our tractors although Castrol Multiuse is fine.

My understanding of the "W" grade is it is related to viscosity, for example; 15/40W has the viscosity of a 15W oil when cold but lubrication characteristics of a 40W when hot.

My experience with Nuffy and Henrietta running on 15/40W semisynthetic was Nuffy covered in oil leaks and Henrietta running the bearings on the crank. Since changing to Morris's 20/50W, Nuffy oil leaks have disappeared and Henrietta runs at 40 psi when at work even when hot with a 66 year old oil pump. (And I mean HOT with a petrol/kerosene engine).
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Re: I don't understand oil wieghts...

Postby Chug-A-Lug » Mon Jun 12, 2017 4:53 pm

Yes thanks Brian, I have found that the first number denotes cold viscosity and the second number denotes viscosity at 100 degrees. Therefore 15w-40 would be 'lighter' at start up and 'heavier' at running temp compared to 20w-30. It seems that 20w-50 is a little specialist, in that it seems to be consistently marketed at vintage machines to reduce leaks and improve performance by better coating warn parts (by way of it's thicker viscosity). I have found many reviews on 20w-50 oil from owners of older machines stating that it does indeed do what it says on the tin and will improve performance of older engines and reduce leaks.

Hope this helps somebody else if they're struggling to understand.

Sam
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Re: I don't understand oil wieghts...

Postby Brian » Tue Jun 13, 2017 8:36 am

If you order 20/50W from Morrises over the internet it will be delivered to your door in a couple of days. Good company that I have known for over 50 years. That was the only oil we used in Nuffields back in the day.

20/50W is also available from Halfords in gallon cans. That is also a good oil.
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Re: I don't understand oil wieghts...

Postby shawnee » Thu Jun 15, 2017 8:54 pm

when you apply the Laws of physics there is no way you can make motor be 15w or 20w when it is cold and 40w when it hot it is a marketing tool . there is no SAE 40w or 50w on that label. The marketing tool of multi grade was not invented or was it? I am sure you all can do some research and figure that out. I disagree with Brian flat out. Prove me wrong.
:roll: :shock: :idea: If it is good or not is beside the point my 1978 mf 285 manual states 30w above 90F, 1967 ford 4000 30w above 75F, 1972 cat d5 30w above 90F , finally 1961 dexta 30w above 90F, multigrade was in use back then. the manual states a single weight oil . you can state you can use diesel fuel for lubrication but that does not mean I going put in my machine because you say mulitweight it's OK!!!!!!!! I do not believe the labeling PROVE ME WRONG!
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Re: I don't understand oil wieghts...

Postby PghBill » Fri Jun 16, 2017 12:38 pm

Shawnee,
Calm down my friend :D Helping to understand multi-grade oil can be found here (https://www.jcmotors.com/images/underst ... cosity.pdf)

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Re: I don't understand oil wieghts...

Postby Jerry Coles » Tue Jul 11, 2017 10:45 pm

The figure used are to indicate to the user the viscosity of the oil when used in the summer and the W bit is the viscosity in winter. Think Colder = thicker. Modern oils contain a lot of viscosity modifiers and other additives and of course these days you can get Normal, semi-synthetic and fully synthetic oils. Oil technology has advanced hugely since the 1950's. Back then most oils were "straight" meaning a single viscosity and for winter time you had to replace all the oil for a different type to operate in colder conditions. Engine design has of course changed dramatically as well requiring higher demands on lubricants, both trying to keep up with each other. The other big change in oil technology was the introduction of "detergent" oils in the 60's. This had a somewhat damaging effect on older types of engine as detergent oils tended to "wash off" oil sticking to surfaces. Older engines with their build up of oil deposits tended to run ok as the deposits used to seal wearing parts etc. When the Army introduced "detergent" oils in the late 60's their huge fleets of old, worn and tired engines suddenly started failing at a catastrophic rate as the new detergent oils were washing away the old deposits and engines just gave up. The chemical composition of a modern oil is a marvel to cater for the demands of modern engines where stresses and temperature are much higher than the older engines we see in our old tractors. Would an oil from the 1950's work in a turbo charged, high revving and greater HP engine of today?? For many old design engines a straight non-detergent oil works best, follow the oil manufacturers like Morris Lubricants recommendations.
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Re: I don't understand oil wieghts...

Postby roromac » Sat Sep 08, 2018 12:14 pm

As I understand it, modern detergent oils work fine in any engine with full-flow oil filters. With that design, the filters strain out all carried particles and the oil returns to the engine clean. The reason old engines often fail when introduced to detergent oil is that the oil filter, if fitted at all, is not full flow. Thus, little suspended particulate matter, carried within the oil, is filtered out. That makes detergent oil an abrasive!
Old oil, and in the UK all SAE30 oils are detergent-free and suitable for old engines, does not carry particulate matter. That becomes "black sludge" in the sump, to be scraped out at rebuild time. The oil can, and sometimes does, circulate without a filter in the system because it allows carried matter to deposit out.
I do not know if Dexta engines have full-flow oil filters or partial-flow filters, maybe someone can help here. I do know that I put detergent oil into my 152 cuin NPSD engine and it now has a crankshaft oil seal leak. It may be coincidence!
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