what oil to use

[jcjdavis1]

Hi I need advice on what oil to use on my 1990 316i with 125ks on the clock. I am using Duckhams now but an oil change is due. Thanks in advance. jcjdavis1

[Globulator]

Best to PM oilman (top stickie on this section).
I'm having much success with full synthetic 0-40 (Mobil 1)

[Adammcf]

I use Magnatec 10W40 in mine. I dont want to go too thin seeing its an old engine.

[stevetigger]

Good old Tesco crap for me, seeing as its an old engine!

[TVRTASMIN]

Mobil 1 0-40 is too thin and too pricey for the BMW.
A good 10W/40 or whatever Duckhams you are using now will be fine.
No need for full synth oils unless you are into serious motorsport and then i would use the 15W/50 version of Mobil 1.

[Globulator]

Mobil 1 0-40 is too thin and too pricey for the BMW.
A good 10W/40 or whatever Duckhams you are using now will be fine.

The xxW figure is of course the winter rating and can be disregarded for a warm engine. The 0W means that the oil flows easily straight from start-up, and therefore is pumped around efficiently saving fuel and getting to where it is needed - like the camshaft, main bearings etc.
At 100degreesC engine temperatures the thinness or viscosity of the Mobil 0W40 will be identical to the 10W40 Duckhams etc - i.e. SAE 40.

To make a petroleum 10W40 you actually start with SAE 10 oil and add a large number of stabilising polymers that can also shear and burn forming deposits, to give you the SAE 40. When the oil wears the polymers break down and the oil thins. Old 10W40 petroleum oil is SAE 10.
To make a synthetic 0W40 is actually easier as synthetic follows a different set of rules than you get when starting out with petroleum, in fact often no polymers are used at all. The shear strength and stability of synthetics is far superior to even the top petroleum oils: It stops time in your engine as wear can be extremely low, as the consistently high shear strength works in your favour. As the oil deteriorates the viscosity can actually increase - the opposite of petroleum oil.

This means that after 5k miles the 0W40 synthetic will be slightly above SAE 40, and the petroleum 10W40 oil will be somewhat below - i.e. it will have got thinner - heading towards it's base 10 SAE. Would you use thin 10 SAE in you car? - well you will if you leave petroleum 10W40 in there for too long. In general therefore we can class synthetic as more stable and generally thicker oil. If you feel the need to use petroleum oil then it is safer to chose one with the thickest base - 20W being a safer starting point, but you will pay for that in fuel when the engine is cold. If you're going to leave it in there for ages then SAE 30 lawnmower oil will be better for you, as there are no polymers to degrade so the single-grade oil is stable.

You are right about the pricey aspect, although CostCo is pretty cheap, and the startup viscosity will probably save me the difference in fuel costs. Because it simply lasts longer than petroleum based oil too you can save by extending oil changes, you might be interested in this test where they get 18,000 miles out of synthetic with a couple of filter changes.

http://neptune.spacebears.com/cars/stor ... -life.html

For my oil I'll change filters at 5k and the oil at 10k. The only thing to watch out for is switching rapidly from a gunky deposit laden engine to an extreme performance oil with high cleaning power, as some of the old gunk can get into the wrong places.

[e30bmlover]

I use Magnatec 10W40 in mine. I dont want to go too thin seeing its an old engine.

as do i my friend

[TVRTASMIN]

A 26 year old high mileage car will not benefit from an expensive full synthetic oil.

Agreed, a proper full synthetic oil will be far superior to part synthetic or normal mineral oil but my advice would be to use the Duckhams or similar and change it and the filter more often, at least once a year or 6K miles whichever comes first.

[Globulator]

I use Magnatec 10W40 in mine. I dont want to go too thin seeing its an old engine.

as do i my friend

Please do not think that synthetic is thin, it isn't. 10W40 oil is stretched a long way (from SAE10 to SAE40 using polymers that degrade. Your base oil is SAE10 - very thin. Magnatec is a good quality oil, I have used it myself, but once you start using it like all pretoleum oils it heads towards its SAE10 base - getting thinner! Synthetic simply doesn't do that, and is also free of sludge forming paraffins etc. It's cold rating will also protect your engine better when starting and cold than Magnatec, because the 0W viscosity will allow the oil to flow round quickly from the pump, as it does not have to battle with over thick oil before the engine has warmed up.

If you think your engine is worn and needs a thicker oil go for 20w50 - SAE50 is thicker than SAE40. Other than wear the oil will not be able to tell how many years old your engine is.

In summary, the SAE rating gives you the thickness:
0W40 synthetic oil is SAE40 and stable
10W40 petroleum oil is SAE40 but declines
20W50 petroleum oil is SAE50 - this IS thicker and more stable than 10W40.

[jcjdavis1]

Hi thanks for the quick reply to my question i should have added that the car does less than 5k a year. does that make a difference as to which oil to use?

[Globulator]

Hi thanks for the quick reply to my question i should have added that the car does less than 5k a year. does that make a difference as to which oil to use?

No, I'd still recommend the same, just change the filter after the first 5k and only the oil after 10k or if it looks too black, or you just fancy a change.
Make sure you check your insurance, if you do limited mileage you can get discounts on your policy.

[Brianmoooore]

1990 316i with 125ks on the clock.

The age of an engine is irrelavent, and 125k is NOT high mileage for a BMW engine.

[gcorky]

fuch-silkolene 5/40 fully sync-extend interval to 3 times the norm if you were that way.


run in my cars -spot on!

[jcjdavis1]

thanks for all your input. jcjdavis1