BMW ambient temp/viscosity chart question

[Ken E.]

For my 22 year old BMWs the owner's manual recommends 15w40 for temps between 0F and 85F. On the single grade side of the chart they recommend SAE 30 for temps between 30F and 85F. 10w-40 is limited to ambient temps no greater than around 50 degrees. Why, when Havoline 10w-40 has higher viscosity numbers at 100C than straight Havoline 30 weight?
I'm asking mainly because I can get Havoline 10w-40 for free, and Castrol GTX 20w-50 which I've used for many years is getting rather dear. Free is a very good price.

 

[nel]

Your owner's manual reflects the quality of oil available 22 years ago. The concern BMW had at that time was viscosity breakdown and the possible sludge build-up from the viscosity index improvers. 10W40 is a large viscosity spread and would quickly shear down, while a mono-weight such as SAE 30 would not.

While oil quality has improved considerably, 10w40 conventional oils will still shear down to a 30 weight. Having said that, I've run Chevron 10W40 in a '97 328i with good results, but I also make sure to change the oil after about 5K miles (even with a 7 qt. sump). Do a search in the used oil analysis section of this forum.

 

[pastmaster]

Ken,

I have an old '79 733i, that fits this situation also. If you don't drive at high performance levels, 100mph cruises and high speed and rpm, Alpine Passes and other sustained high speeds, you're OK, with the 10W40. If you're driving around town and 50mph country lanes, and a blast up to redline a few times a day, it's OK. Free is Free.

German Car You Know.

Just watch your use level.

 

[TomJones76]

What nel said.
The chart reflects some pretty dodgy 10W40s that were current in the early 1980s.
Modern 10W40s are more capable, and Havoline is a particularly well-liked brand here.
Drive happy!

 

[Jimbo]

Be careful. My 1992 325i drinks 10W40 Syntec while merely sips 15w40 Delo. That seemingly slight difference in viscosity made a 3x difference in oil consumption. BMW dealers sell 15w40 conventional for the older cars. Im not saying it wont work, just check the oil level frequently until you know how your engine likes it.

 

[hominid7]

My '89 Jetta's owners manual read very similar to yours. I experimented with various oils, but finally settled on conventional 20w50 year-round. I found that anything thinner would set off either the oil pressure warning buzzer or the temp warning light.

I do not believe it was an actual problem with the oil so much as it was a german electronic design that did not account for 110*F Texas weather. The 20w50 was more or less a band-aid for a less than perfect oil pressure monitoring system.

Having said that, i drove the car 225,000 miles over 11 years and never had ANY engine or transmission problems or ever burned a drop of oil. I used Valvoline and Napa branded Valvoline 20w50 conventional and changed it at intervals of 3000 or less and red-lined it weekly throughout it's long and reliable life.

I replaced the valve cover gasket at 150K and the engine was spotless.

I'd stick with 20w50 if it was my car. If you want to save money try a cheaper oil like Napa brand dino, Exxon Superflo, or Havoline.

 

[Ken E.]

hominid7, the idea was that the Havoline 10w40 was the best oil available to me for free, which is a big savings over even the cheapest on-sale dino. Alternately, I can also get for free either Havoline straight 30wt or "76" brand 20w50. I suppose the answer is the most obvious, just switch from expensive Castrol to free "76" 20w50, ignore the inner oil-snob living in the back of my head, and change the oil fairly often...duh.

This is one of the problems of being an obsessive/compulsive BMW owner: I spend way too much time in internal debate.

 

[hominid7]

76 is a ConocoPhillips brand and the ConocoPhillips family of brands has proven itself time and time again with quality lubricants at a decent price. I would not consider it any less of an oil than Kendall, Motorcraft, TropArtic, etc... Here is a link to the spec sheets for 76 oils:

http://www.76lubricants.com/ProductDataSheets/Crankcase.htm

Havoline 10w40 is a pretty thick and hearty 10w40 and it will likely be pretty shear-resistant. People have turned good wear numbers in with it and it seems to hold up. Considering your climate, the 10w40 may be just fine. I would highly recommend it over the straight sae30.

So chances are either the 76-20w50 or the Havoline 10w40 would likely be ok in your car. If this is a "cruiser" and not a "racer" it might not be an issue. Since you have previously been running 20w50 and your car seems to have had a long life on it, i might be tempted to stick with that though.

Another option may be to use the Havoline 10w40 in the winter months and the 76 20w50 in the summer months. Either way you'll probably be ok

 

[Ken E.]

BrianWC, my wife's cousin is a BMW nut, though mostly for status rather than performance. He uses Castrol 10w40 in his cars because "the owner's manual recommends it." I don't have the heart to tell him that, for this climate, it does not . That said, he puts literally hundreds of thousands of miles on his cars and has never had any oil or excessive wear issues. He is not, to say the least, troubled by the obsessive/compulsive nonesense that I am. He just changes oil occasionally and drives his car. I envy him.

 

[BrianWC]

I would have used bleepin' Rotella if I had known what the owners manual was recommending.

At the time, all I knew were straight weights, 10W30, and 10W40.

That M10 engine would have run on spit if necessary. It was pretty stout.

 

[G-MAN]

10w40s were the absolute worst oils back then. GM stopped using 10w40 as factory fill in 1980 because of premature cam lobe wear. They actually put big warnings in the owners manuals that stated not to use 10w40.

The base oils and VI improvers used back then were just not up to making a 10w40 that could protect over the typical OCI of 5000 to 7500 miles. That has all changed now, of course, and the 10w40 grades of any name brand oil are just as good as the other multi-grades.

 

[Ken E.]

BMW engines are stout. If I had my way right now I'd turbo the one in the 533i. Alas, finances preclude massive HP at this point.

 

[BrianWC]

My '82 320i always had Valvoline AC 10W40 changed out at 3k intervals. Silly me. All I knew was it was "the choice of more mechanics." Never used a drop though...As long as you change it...