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#98583 - 08/26/04 06:44 PM 15-40 vs. 20-50???
Dr. T Offline


Registered: 05/28/02
Posts: 2480
Why is the 15-40 listed as a Heavy Duty (HD) oil and not the 20-50? Which one has more cojones, less volatility and burnoff? Wouldn't the 20-50 provide more high-stress protection or is it overkill and the 15-40 is more of a middle ground for 'fleet use'?

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#98584 - 08/26/04 06:57 PM Re: 15-40 vs. 20-50???
TallPaul Offline


Registered: 10/22/03
Posts: 12915
Loc: By Detroit
quote:
Originally posted by Dr. T:
Why is the 15-40 listed as a Heavy Duty (HD) oil and not the 20-50? Which one has more cojones, less volatility and burnoff? Wouldn't the 20-50 provide more high-stress protection or is it overkill and the 15-40 is more of a middle ground for 'fleet use'?

Very good point. Why are there so few passenger car 15w40s? I know of one passenger car 15w40 (which also has light diesel rating--not count for HD): Valvoline Durablend.

As for the cojones of the 15w40's base oil, I see the API chart shows both 15w and 20w have to meet the same minimum low-sheer-rate kinematic viscosity (cSt) at 100C of 5.6. And both have to meet the same minimum high-sheer-rate viscosity (cP) at 150C of 3.7. So I am wondering if there is any difference in the base oil between the two. It may all be in the adds (primarily more cold property adds), but perhaps the 20w50 has a somewhat thicker base oil. The only place the API chart differs for these two oils is in low temperature cranking viscosity and low temperature pumping viscosity.

Chart: http://www.infineum.com/information/viscosity.html

Once upon a time they had 20w40. I wonder if that was the predecessor to 15w40?

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#98585 - 08/26/04 06:59 PM Re: 15-40 vs. 20-50???
T-Keith Offline


Registered: 01/20/04
Posts: 4865
Loc: MN
15w40 is the recommended weight for many diesel engines. The requirements for diesel engines are greater, hence the Heavy Duty designation. 20w50 a pretty old spec used for some gas engines, they usually don't mean diesel standards so they don't get the heavy duty label. I see no reason to use 20w50 over 15w40 in any engine.

-T

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#98586 - 08/26/04 08:44 PM Re: 15-40 vs. 20-50???
Jimbo Offline


Registered: 02/13/03
Posts: 1347
Loc: California, USA
Paul,

20W-40 was a very popular Euro-spec oil in the 1970's. I used it in VW's, Jaguars, etc. 15W-40 is the functional replacement in Europe. 15W-40 is the only grade available in BMW's conventional motor oil.

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#98587 - 08/27/04 09:08 AM Re: 15-40 vs. 20-50???
TallPaul Offline


Registered: 10/22/03
Posts: 12915
Loc: By Detroit
quote:
Originally posted by Jimbo:
Paul,

20W-40 was a very popular Euro-spec oil in the 1970's. I used it in VW's, Jaguars, etc. 15W-40 is the functional replacement in Europe. 15W-40 is the only grade available in BMW's conventional motor oil.

What do they do with the BMW's running their 15w40 during winter? Does the BMW 15w40 have special cold properties to make it winterable? So I could walk into a BMW dealer and buy their 15w40, but probably cost prohibitive, aye?

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#98588 - 08/27/04 09:31 AM Re: 15-40 vs. 20-50???
Dr. T Offline


Registered: 05/28/02
Posts: 2480
Well it still gets a W rating! My BMW chart goes down to -20C with a 15W.

I want to say that I had the BMW 15-40 stuff accidentally put in when I had an oil change done at the dealer since it was on the bill and I requested the synthetic. Both the Service Manager and the mechanic said I got a freebie on the invoice since he put in the synthetic. But couldn't prove it other than to say he still had the empty box the bottles were in. But, they do 20 oil changes a day....how would one remember. In either case, I would say it's a better oil that the 5-30 synth. believe it or not... [Cool]

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