Topic: 10w40 vs 20w50

[phil71]

been running castrol motorcycle 10w40 in the k1 for a few weeks. Shop Manual says "10w40 or 20w50" but makes no recommendation as to what conditions want which viscosity. I've tried both, and find shifting easier and the clutch is quieter with 20w50.. is there any good reason not to just run that all the time? I don't use it much in the wintertime..

[nancy]

Phil
10w40 in the cool and 20w50 in the heat...
regards
Mark

[lone*X]

A very general answer.   10w40 in cold climates.  20w50 in hot climates.   10W flows better in cold conditions and aids in cold starts but is not need in hotter climates.  When it gets really hot the 50w doesn't thin out as much as lower viscosity oils. 

If you store it during the winter then run the 20w50 all the time.

[TwoTired]

been running castrol motorcycle 10w40 in the k1 for a few weeks. Shop Manual says "10w40 or 20w50" but makes no recommendation as to what conditions want which viscosity. I've tried both, and find shifting easier and the clutch is quieter with 20w50.. is there any good reason not to just run that all the time? I don't use it much in the wintertime..

Three different SOHC4 owner's manual's (74 CB550, 77 CB550, and 77 CB750F) state 10W-40 for all temperatures.  None of these state that any form of 50W oil is appropriate.
The 72 CB500 O.M. does state that 20W-50 can be used if the temps are 59F or above.

Shifting is always easier right after an oil change (before the gears and such have and time to chop up the long chain molecules in the additives that allow the oil to behave thicker when hot).  Doesn't really matter which of the two viscosities chosen.

I find it odd that anyone would believe internet opinions or folklore to be of more use than the owner's manuals.
How many internet writers have done lifetime tests comparing different oils?
How many testimonials were done double blind so the end results weren't tainted by personal bias?
I firmly believe that most internet recommendations and based more on what makes the owner feel good rather than any actual science that supports a recommendation.

Ugh, another friggin oil thread...

[HondaMan]

been running castrol motorcycle 10w40 in the k1 for a few weeks. Shop Manual says "10w40 or 20w50" but makes no recommendation as to what conditions want which viscosity. I've tried both, and find shifting easier and the clutch is quieter with 20w50.. is there any good reason not to just run that all the time? I don't use it much in the wintertime..

I've used 20w50 (Castrol) for 138,000 miles in my K2 (which came new with a K1 engine in late 1971) except in deep winter, then 10w50. Don't use 10w40 in the 750 in warm weather: the shift drum gets sticky, the gears drag on the shafts, and the clutch plates can warp from the too-thin oil not carrying away enough heat.

[vames]

I find it odd that anyone would believe internet opinions or folklore to be of more use than the owner's manuals.
How many internet writers have done lifetime tests comparing different oils?
How many testimonials were done double blind so the end results weren't tainted by personal bias?
I firmly believe that most internet recommendations and based more on what makes the owner feel good rather than any actual science that supports a recommendation.

Um...have you read every single honda service manual? Then how can you claim to know what every single honda service manual says? Have you done a lifetime test comparing different honda service manuals? Below is page 178 of the Honda CB750 service manual. Exactly as OP stated, it says "10W-40 or 20W-50" without any qualification of which would make you choose what.



Phil -- summer usually being very hot and humid in NYC, and with the amout of red lights we sit at, I'd suggest you go for the 20-50 in the warm months and drop back to 10-40 in the fall. That's what I do.

[HondanutRider]

Oh-oh, another oil thread....

I know it's been stated before that 20W-50 was the recommended oil for the CB350F.  I'm not familiar with other models, but my 1974 CB350F Owner's Manual has only one reference to this weight of oil, listing it as one of the two recommendations in the section for changing the oil and oil filter element on page 38.  To quote: " Fill the crankcase with approximately 3.7 U.S. qt. (3.5 l) of premium quality, SE, SAE 10W-40 or 20W-50 oil or its equivalent."  This is the only reference to 20W-50 that I can find in my manual.  On page 27, it lists the recommended oil viscosity; quoting from this page below:
_______________________________
General
  All Temperatures SAE 10W40

Alternate:
  Above 59*F (15*C) - SAE 30
  32* to 59*F (15*C) - SAE 20 or 20W
  Below 32*F  (0*C)   - SAE 10W
_______________________________

Further to the quoted references from the Owner's Manual, the oil dipstick/filler has embossed on it "Use SAE 10W-40".

Looking at the Honda Shop Manual for the CB350F-CB400F, it lists the following in the section for Changing Oil:

Recommended Oil: SAE 10W-40 (All weather)
                              SAE 20W50 (Above 59*F or 15*C)

Based on what this last manual states, I would conclude that for the smaller SOHC4's, 20W50 would only be recommended if the temperature was consistently above 59*F.  Using this viscosity of oil when the temperature is lower might lead to poor circulation and consequently excessive wear or damage, particularly at start-up.

[Skunk Stripe]

I know this might shock some people but I think the manual is somewhat irrelevant. Fact is, oil is better these days then back in the 70s. In 1999, more stringent standards were put into place regarding oil viscosities and flow points. Prior to 99, the last major change was in 1952 and in 1911 the SAE J300 was created.
Not only that, detergent packages have changed.
With today's oils, a 10-40 is likely to protect sufficiently for almost all conditions. The use of 20-50 would also be absolutely fine except for below freezing and that is more because the engine has a hard time warming up.
Heat is the other end of the spectrum and as such, the weight also has a measurement which is done at 100C or 212F. In addition, for SAE grades 20, 30, and 40, a minimum viscosity measured at 150 °C (302 °F) and at a high-shear rate is also required.
So, really, a 10-40 will provide plenty of protection, even in upper heat ranges. If you need the small addition of 50 weight, maybe an oil cooler is a better option.

My opinion is that the manual was correct in the 70s and is just accidentally so now. A 10-40 oil will cover virtually all ranges required for our bikes. Only time I would see 20-50 in use would be if your engine is tired and worn and you are putting off rebuilding.


http://www.ideas4ag-ed.com/uploads/3/7/0/4/3704787/stan_toepfer_understanding_motor_oil_viscosity.pdf

[Markcb750]

I use a different type of oil every time I change, always 10w 40, except in summer when I run 15 w 40, unless I cannot find it, then I run 20w 50.

Unless I have some 10w 40 around the shop, then I just use it, even if it is not a "different" type of oil.

So, I guess my original statement was more of a general concept, not a personal commitment.





BTW:

I re-polish my oil filter housing every time I change the oil.


I add a little Sea-Foam to the oil about 100 miles before I change it, unless I forget, or the mood to wrench & polish hits me and I just change the oil.

[phil71]

OH crap. I did not mean to go down that road, and create another oil thread. I'm sorry everyone.