How choose a good oil for an M30 engine.
Posted: Sat Apr 02, 2011 9:19 pm
I've read widely on the subject of oils, including the LN engineering web pages. From this I've compiled some brief notes on oils for M30s. Mostly this is a 'precis' of information from elsewhere but where I've expressed my own opinion I have indicated it as best I can.
1. M30 has a two-valve head with strong springs and a high rocker ratio. This means that cam follower loadings are very high, much higher than those seen in many modern oil performance tests which tend to simulate modern 4V valvetrain loadings. Some older valvetrain wear test sequences (VE, VD) which simulated the M30 more closely are now thought less relevant to new oil testing.
2. ZDP (AKA ZDDP) is required to prevent 2V valvetrain wear, and some detergentcy is required to deal with ZDP breakdown products. However the required amount of ZDP increases with yet higher levels of detergent. High detergent oils (e.g. for extended drain intervals, especially Calcium based detergents) cause more wear at the same ZDP levels than lower detergent oils.
3. API SE, SF, SG, SH, SJ rated oils (from a time now passed when 'newer spec = better oil' was the rule) typically have good levels of ZDP and moderate detergent levels. However API SL oils may have much lower ZDP levels (unless other specifications are also met). Valvetrain wear problems apparently increased suddenly with the introduction of API SL. API SM or higher rated oils will almost certainly have ZDP levels that are too low for an M30. (ZDP is not used in these oils in part because of newer emissions/catalyst requirements. Very high ZDP levels can kill catalysts.)
4. API CF rated oils will also have high ZDP levels and moderate detergent levels (lower detergent than, say, CI rated oils) so should make the best of the ZDP present.
5. ACEA A3/B3 rating is overall a good thing. Valvetrain scuffing wear limits are typically ~1/5th of those allowed in (say) API SM testing. Also many other properties of the oil when hot are tested more stringently than API-only rated oils. However there is a catch; ACEA A3/B3 rating implicitly limits P to 0.1-0.12 maximum; this may be sufficient in an M30 only if the oil meets some other specifications as well.
6. LN engineering recommend 0.12-0.14 Zn and P for air-cooled Porsche engines (higher valvetrain loadings and oil temperatures than the M30 as I understand it). They suggest one route is to use STP to slightly boost Zn and P levels in a good quality ACEA A3/B3 oil.
7. My M30 suggestion is to find an oil which meets no more than API SL (or preferably SJ or lower), API CF ( but not higher) and ACEA A3/B3. The API SL and the ACEA specifications confer many good things in the oil, but do not guarantee very high Zn and P levels (although they may cap them). However the API CF rating ensures fairly high Zn/P levels and a moderate (but not excessive) detergentcy.
8. Oils meeting the specifications above should be OK in a 6er for the standard drain interval, provided filtration is OK, oil pump/pressure is good, and blowby etc is not excessive. I would not recommend extended drain intervals or indeed many of the oils that give extended drain intervals in other engines. Remember that generally the more miles the engine has on it, the more likely it is that the oil will slip out of grade earlier rather than later.
9. In my view there is nothing wrong with changing the oil more often than normal. There are loads of healthy high mileage engines out there which have had the oil changed once every four thousand miles or so. You may read that wear particles in the oil may increase immediately after an oil change; I believe that this may be the cleaning action of new oil (with fresh detergent action) releasing bits of trapped crud from various nooks and crannies in the engine. This sort of thing is very much more likely in an air-cooled engine IMOE. Unless you plan to never change the oil again this cleaning action is inevitable, so it is a question of choice here; a little and often or infrequently but a lot more. Fitting a magnet to catch all this crud seems like a very good idea.
10. The saving grace in the M30 may be oil temperature. I would be surprised if the oil was routinely in excess of 120C in the rocker box, where with (say) air-cooled Porsche engines it could be much higher than this. Higher oil temperatures of course lead to greater emphasis on the requirement for anti-scuffing additives.
11. To date all cam wear problems in M30s that I have seen personally are likely attributable to a simple oil supply problem of some kind, not to the finer points of lubricant selection. Having said this, why take a risk? In fact some of the oils that will work in an M30 are cheaper than supposedly 'better' oils that are in fact less suitable.
12. My daily driver's handbook (for turbocharged DI diesel) explicitly prohibits the use of API CG or higher rated oils; API CF is what is required, presumably for reasons related to the ZDP issue. I have recently rationalised my oil selection; I have just bought a large container of a Comma 15W-40 API SL/CF, ACEA A3/B3 rated oil from my local auto parts shop. This will go in my daily driver, my land-rover, and of course my 6er. Previously I had different oils for each which was a bit of a logistical nightmare.
13. Fully synthetic, semi-synthetic or mineral? For reasonable drain intervals in an M30 used on the road, really I don't care which just as long as it meets the correct specifications. Many of the alleged 'benefits' of fully synthetic oils relate to extended drain intervals, or are assured by the correct specification (especially the ACEA A3/B3 tests) anyway. However for tuned/turbo engines or hard track use there is a good argument for a different oil to be used. There are some good suggestions on the LN engineering webpages.
14. Which viscosity should I use? An easy one this; just follow the guidance in the owner's handbook depending on the climate. Having said this 15W-40 will be fine nearly everywhere in fact; it'd have to be really cold or unbelieveably hot before BMW would prefer that you don't use it.
I hope you find all this useful; all comments welcome.
cheers
1. M30 has a two-valve head with strong springs and a high rocker ratio. This means that cam follower loadings are very high, much higher than those seen in many modern oil performance tests which tend to simulate modern 4V valvetrain loadings. Some older valvetrain wear test sequences (VE, VD) which simulated the M30 more closely are now thought less relevant to new oil testing.
2. ZDP (AKA ZDDP) is required to prevent 2V valvetrain wear, and some detergentcy is required to deal with ZDP breakdown products. However the required amount of ZDP increases with yet higher levels of detergent. High detergent oils (e.g. for extended drain intervals, especially Calcium based detergents) cause more wear at the same ZDP levels than lower detergent oils.
3. API SE, SF, SG, SH, SJ rated oils (from a time now passed when 'newer spec = better oil' was the rule) typically have good levels of ZDP and moderate detergent levels. However API SL oils may have much lower ZDP levels (unless other specifications are also met). Valvetrain wear problems apparently increased suddenly with the introduction of API SL. API SM or higher rated oils will almost certainly have ZDP levels that are too low for an M30. (ZDP is not used in these oils in part because of newer emissions/catalyst requirements. Very high ZDP levels can kill catalysts.)
4. API CF rated oils will also have high ZDP levels and moderate detergent levels (lower detergent than, say, CI rated oils) so should make the best of the ZDP present.
5. ACEA A3/B3 rating is overall a good thing. Valvetrain scuffing wear limits are typically ~1/5th of those allowed in (say) API SM testing. Also many other properties of the oil when hot are tested more stringently than API-only rated oils. However there is a catch; ACEA A3/B3 rating implicitly limits P to 0.1-0.12 maximum; this may be sufficient in an M30 only if the oil meets some other specifications as well.
6. LN engineering recommend 0.12-0.14 Zn and P for air-cooled Porsche engines (higher valvetrain loadings and oil temperatures than the M30 as I understand it). They suggest one route is to use STP to slightly boost Zn and P levels in a good quality ACEA A3/B3 oil.
7. My M30 suggestion is to find an oil which meets no more than API SL (or preferably SJ or lower), API CF ( but not higher) and ACEA A3/B3. The API SL and the ACEA specifications confer many good things in the oil, but do not guarantee very high Zn and P levels (although they may cap them). However the API CF rating ensures fairly high Zn/P levels and a moderate (but not excessive) detergentcy.
8. Oils meeting the specifications above should be OK in a 6er for the standard drain interval, provided filtration is OK, oil pump/pressure is good, and blowby etc is not excessive. I would not recommend extended drain intervals or indeed many of the oils that give extended drain intervals in other engines. Remember that generally the more miles the engine has on it, the more likely it is that the oil will slip out of grade earlier rather than later.
9. In my view there is nothing wrong with changing the oil more often than normal. There are loads of healthy high mileage engines out there which have had the oil changed once every four thousand miles or so. You may read that wear particles in the oil may increase immediately after an oil change; I believe that this may be the cleaning action of new oil (with fresh detergent action) releasing bits of trapped crud from various nooks and crannies in the engine. This sort of thing is very much more likely in an air-cooled engine IMOE. Unless you plan to never change the oil again this cleaning action is inevitable, so it is a question of choice here; a little and often or infrequently but a lot more. Fitting a magnet to catch all this crud seems like a very good idea.
10. The saving grace in the M30 may be oil temperature. I would be surprised if the oil was routinely in excess of 120C in the rocker box, where with (say) air-cooled Porsche engines it could be much higher than this. Higher oil temperatures of course lead to greater emphasis on the requirement for anti-scuffing additives.
11. To date all cam wear problems in M30s that I have seen personally are likely attributable to a simple oil supply problem of some kind, not to the finer points of lubricant selection. Having said this, why take a risk? In fact some of the oils that will work in an M30 are cheaper than supposedly 'better' oils that are in fact less suitable.
12. My daily driver's handbook (for turbocharged DI diesel) explicitly prohibits the use of API CG or higher rated oils; API CF is what is required, presumably for reasons related to the ZDP issue. I have recently rationalised my oil selection; I have just bought a large container of a Comma 15W-40 API SL/CF, ACEA A3/B3 rated oil from my local auto parts shop. This will go in my daily driver, my land-rover, and of course my 6er. Previously I had different oils for each which was a bit of a logistical nightmare.
13. Fully synthetic, semi-synthetic or mineral? For reasonable drain intervals in an M30 used on the road, really I don't care which just as long as it meets the correct specifications. Many of the alleged 'benefits' of fully synthetic oils relate to extended drain intervals, or are assured by the correct specification (especially the ACEA A3/B3 tests) anyway. However for tuned/turbo engines or hard track use there is a good argument for a different oil to be used. There are some good suggestions on the LN engineering webpages.
14. Which viscosity should I use? An easy one this; just follow the guidance in the owner's handbook depending on the climate. Having said this 15W-40 will be fine nearly everywhere in fact; it'd have to be really cold or unbelieveably hot before BMW would prefer that you don't use it.
I hope you find all this useful; all comments welcome.
cheers