Oil weight

[purplecty]

What is the proper oil weight you guys are using for the M70. Specifically a 91 850i?

Im thinking 0w40 is ok?

[dragon850]

5w40

[Sniff38]

I'd recommend you refer to your owner's manual then make a determination based on your expected driving conditions (i.e. exterior temperature). There are several recommended oil viscosities, but 0W40 is not one of them (I just looked at a 1991 850i manual). Personally I don't claim to know more than the BMW engineers, so I don't take any chances. I use 20W50 because I live in a relatively warm climate but it does get rather chilly here in the winter months (but usually not below freezing).

You'll find the BMW collector community has a lot of passionate opinions when it comes to oil (it's the same way in the Porsche world). There are plenty of oil threads out there so use Google search and you will come across more opinions than you will ever need.

Sean

[purplecty]

The manual is from 1991 though and in sure it was referring to mineral oil? When i look up oil change kits on ECS TUNING it shows 5w30 as the oil weight. When i found Mobil1 0w40 on ECS TUNING it shows it will work for the 850i...

[radlaw]

Depends on the temperatures where you live. Southern California oil weight is different from Chicago's.

[henryc]

When the owners manual refers to mineral oil, it means regular engine oil- as opposed to synthetic oil like Mobil1, Castrol Edge, et al. I use Castrol GTX (mineral oil) 20W50 in my E31, and change the oil and filter every 3,000 miles (or 5,000 kms). As mentioned earlier, everyone has their favorite brands, engine oil weights (viscosity) and opinions about why they use what they use. As also mentioned by Snif38- I too recommend using your owners manual recommendation for the engine oil viscosity. Those engine engineers at BMW are probably more knowledgeable about what works best (and hence the recommendation list provided in the owners manual) than folks who may or may not have an engineering degree at a parts house. Granted, engine oils have seen a lot of development since that owners manual was printed, but sticking with the factory options regarding engine oil viscosity would be my recommendation. Good luck! /HenryC

[XAlt]

Muh Castrol GTX so I can't crank. It's fine for SoCal, not Chicago winter. I've run Rotella T6 in my friend's E32 750 for 30k miles (with changes every 8k) at this point, and it runs like a sewing machine.

Synthetic 0w40\5w30\40 is called for in the later M73. Early M73 and M62 cars technically shipped with 15w40\20W50 dino and changed over to 5W30\40 syn as soon as they could.

[purplecty]

Muh Castrol GTX so I can't crank. I've run Rotella T6 in my friend's E32 750 for 30k miles (with changes every 8k) at this point, and it runs like a sewing machine.

I'd use the synthetic 0w40\5w30\40 called for in the M73. Early M73 and M62 cars technically shipped with 15w40\20W50 dino and changed over to 5W30\40 syn as soon as they could.

I am a fan of rotella T6 and may recommend this to my friend...

[KRUZEN840]

First off, great looking E38! Currently on my third, a 2001 740i Sport, which will soon be approaching your mileage achievement! Best long distance cruisers I've ever owned, and with the sport package can easily outrun my stock 840Ci.

BMW oil recommendations are by far your safest starting point for viscosity. The recent growth in "0" multi-weights is more closely associated with EPA and CAFE numbers than protecting your expensive German engine! Unless your car is parked outside in minus 10 degrees regularly, I have always maintained a 10W30 winter oil and changed to 10W40 for summers. Once my cars pass the 125,000 mile mark I feel they've earned a little more summer viscosity, so they receive 15W50 or 20W50. Mobile One has served me well the past 15 plus years with no oil consumption from any motors, even when extending my daily drivers to 8000 mile oil changes, E38, E39.

On my CSi (S70) I follow the same recommendations as any standard BMW engine, as I've never seen anything in print from BMW that would imply the S70 engine receives greater bearing or piston clearances, which truly among the most important reasons for increased viscosity.

With 48 BMW pistons to keep oiled, a common way some friends at our weekly Car & Coffee describe their addiction, I've found Walmart 5qt. containers of Mobile One the cheapest and simplest way to perform my oil changes. You get some strange looks when you checkout with $300. of Mobile One in your cart.

Good Luck!

[KRUZEN840]

Oil numbers are about viscosity with respect to climate temperature, and how the oil stays in the top of the engine (sticky). A thin oil that is not sticky will all be in the oil pan in a warm climate if the car sits. That means the top of the engine will get dry when sitting. The owners manual has a chart for temperature (climate) and oil number. When the engine has warmed up all the oils no matter what number are operating at the engine temperature that is controlled by the thermostat.

Oil viscosity is about an oil's ability to flow through a given opening, when pushed by a given amount of pressure, at a given temperature. The actual numbers, commonly referred to as SAE ratings, 10W-40, 20W-50 are all about flow. These numbers are assigned all oils by the Society of Automobile Engineers- SAE.

Single weight oils have no ability to change their flow rates depending on the cold temp/starting temp of the engine. Dino oils, much like maple syrup, will drastically alter this flow
rate based on their temperature. A can of 50 weight oil will pour like cold honey in minus 10, 20 degree temps. Bring that same oil inside, warm it to 100 degrees, and it will flow like hot maple syrup.

Engines will have different viscosity requirements based upon the clearances engineered into them, usually based upon application. Clearances represent the differences engineered between piston dia. and cylinder wall dia., crank shaft dai. and rod bearing dia., etc. If the oil is too heavy, high viscosity, it won't flow past the oil pump to the crank bearings, etc. when cold, at startup. However, if that oil is too light it will not be able to protect the rod bearings from actually hitting the crankshaft at high rpm, as the oil is literally push out of engine bearings. High viscosity oils, 50, 60, are very hard to push, thin oil, less protection. BMW "S" motors often have a requirement of 10W-60 oil. The first number is how that oil will flow at low temperature, such as starting your car in winter outside, the second number, 60 is how that oil flows when warmed, which SAE places a "W" after the first number to indicate it's a Winter flow rate. The second number is the flow rate once the engine reaches operating temperature. How many fluids do you know that thin when cooled and thicken when heated?

EPA testing requirements are a major force behind "0" weight oils. Every drop of fuel consumed by the test engines is counted towards it's fuel EPA numbers. Cold starts are required, so very low viscosity oils offer very little resistance to the engines moving parts during start up. Less resistance , better fuel EPA numbers.

Being a little "old school" on manufacture requirements and recommendations, not trusting them all, like "lifetime trans fluid", "lifetime antifreeze", "0W-20" oil, I always look for at least a 10W winter oil and 15W or 20W summer oil.

Now picking a "BRAND" of oil really starts opinions flying! Opps, I mean flowing! :-)

[blanz]

Read this:
http://www.animegame.com/cars/Oil%20Tests.pdf

I'm now running Royal Purple 20W50 (I live in Georgia where it is rarely below freezing) after reading this article. This higher weight oil quieted the engine down a bit and no issues at startup or consumption.
And this straight from the owners manual:
Oil weights from owners manual.png

[purplecty]

I was really just looking to see what oil weight and brand you guys are personally using... I am now leaning towards 5w40 or 0w40...

[tvjake2]

I was really just looking to see what oil weight and brand you guys are personally using... I am now leaning towards 5w40 or 0w40...

Rotella T6, 5-40w in both cars.

[purplecty]

Rotella T6, 5-40w in both cars.

You have an M60 not M70 correct?

[XAlt]

Add pack always triumphs over weight.

Rotella T6 is good enough for 14 liter diesel engines idling for hours, good enough for superbikes, and it's good enough for a WRX cooking its turbo. And guess what, it's just a 5w40.

praise holy zinc

[drphysic]

I have always consulted Mike Miller, BMW CCA Tech Editor, when considering oil issues. I just checked with him recently again on M70 oil viscosity specifically about low viscosity oils. He supports using BMW's recommended viscosity, since no matter what the oil is made of, its viscosity numbers are based on flow, as described in an earlier post, and the reason for using a given viscosity based upon local temps, hasn't therefore changed. I use 15W-50 in southern New Mexico as it covers the anticipated temperature extremes.

Note that to determine oil change intervals, nothing beats using Blackstone Labs oil assay, again as Mike recommends. I recently did that for the wife's Volvo V70 with 160K miles, after using Mobil 1 for 10K miles, and the lab test showed it could go for 12K between changes without loss of its performance. The E31 will get that at its next oil change as well.

[MonsterJam]

I use Castrol mineral 5W30 in Toronto, as per car specs.
When I used synthetics on cars that did not call for synthetic oil I ended up with oil leaks.

Question to the group, would it be better expanding the temp range, i.e. Same oil but 0w40 would it be better than 5w30? This question is strictly about the weight not the brand or type?

[XAlt]

I use Castrol mineral 5W30 in Toronto, as per car specs.
When I used synthetics on cars that did not call for synthetic oil I ended up with oil leaks.

Question to the group, would it be better expanding the temp range, i.e. Same oil but 0w40 would it be better than 5w30? This question is strictly about the weight not the brand or type?

Err, gaskets. The synthetic was cleaning out dried gasket material/sludge and also tends to be much smaller molecularly hence the oil leaks from worn gaskets. The smaller crevices tend to get filled by swell sealers, and hence the "it'll get worse before it gets better" reports. If you haven't tackled it yet, I'd take care of them.

0w40 would have more tolerance when it shears down (i.e a 30 weight at the end of its service cycle, as with most 40s) You'll have the best cold start protection (but also louder valvetrain noise when cold and less heat tolerance (conservatively said to be good up to 90F, but you'll want 15w50 at that point) and thicker when hot (which is fine, the M62 loves thick oil)

[tvjake2]

you have an m60 not m70 correct?

M62...but it wouldn't matter. I know a number of M70 guys that use this oil.

[peezen]

Yup, Rotella T6