Originally Posted By: Nick26
I read on the BMW forum that my car needs a high Zinc oil.
The OP was probably referring to me.
There seems to be a lot of hate on xW50 multigrade oils in this thread and that surprises me. With OEM cam and rockers the M20B25 engine has ~175psi(1) of peak nose pressure. My perception is that a HTHS #'s better than 4.0cS for that much spring pressure is preferred and certainly above 3.7 or so. Some xW40's have HTHS #'s >4.0, but most do not. That would indicate to me that thinner oils for Winter use should be chosen with care. Brad Penn and Swepco come to mind.
It's no slam dunk tho. The owner's manual for the M20 recommends 20W50 has a hot summer oil.
http://www.gress.org/Home/Cars/TrackTale...anualOilRec.htm
But a 2005 BMW technical document re. oil choices reduces the emphasis on xW50 in favor of 10W40. Perhaps because the HTHS #'s for xW50 in the early 1980's were in 2005 being achieved by xW40's.
http://www.gress.org/Home/Cars/TrackTale...cs-and-Recs.pdf
Things to note in the docs.
1) Reduced emphasis on 20W50. The doc is kinda hard to puzzle out because I don't have the appendices, but areas B&D of the diagram would both seem to apply and D has no xW50 even listed.
2) 20W50 is specified of having a lower limit of -10deg. I wouldn't choose 20W50 as a winter oil, but I don't understand all that hate here for 20W50 as a summer oil.
3) The M20 is listed at the bottom as an "Other" engine.
Another factor that might play into BMW's later reduced emphasis on xW50 for the M20 is that later engines ran cooler oil temps. The early models did not have oil coolers. I race the same car the PO owns and have experimented with various oil related ideas. W/o an oil cooler oil temps will happily hit 245deg. W/ an oil cooler they don't seem to go over 225deg.
The issue continues to be ambiguous. Here's a BMW doc that says both "Use the oil in the owner's handbook" (high temp oil is 20W50), but also says "Use 5W30 or 15W40" (at the end of the doc). The reference to the lighter oils tho is suspect because BMW is recommending using what they sell, as opposed to recommending using what they don't sell.
http://www.lindvigs.com/obioban/BMWEngineOils.pdf
Thick oil is not dead at BMW. I believe the last couple generations of BMW M3 used a Castrol TWS 10W60, indicating that reports of the demise of thick oil might be premature. Certainly the guys racing M3's seem to prefer a thick oil to handle the high oil temps.
Here's an interesting thread re. the M3 and Castrol TWS 10W60. Note the discussion of how the BMW Marketing department influenced the decision making.
http://www.m3forum.net/m3forum/showthread.php?t=295656
I'm surprised at the reduced emphasis on ZDDP in this thread. Sure, there's been work done on substitutes, but the folks that seem oriented on old-school 2 valve engines and their stiff valve springs still seem to be oriented on ZDDP, no? I don't see that Navarro, for example, has changed his mind.
http://www.lnengineering.com/oil.html
http://forums.pelicanparts.com/porsche-9...j4-sm-oils.html
@Doug Hillary. Sir, about 5yrs ago I was doing a lot of research on oils. I found a lot of your stuff and read it thru many times. Thanks for your efforts to educate folks.
Note that I'm not arguing with y'all, I want to learn. Support the case you're making for staying away from xW50 as a summer oil, and that ZDDP isn't that big of a deal anymore for old school engines with big valves and strong springs.
PO. I wouldn't worry about e10 gas. Most everyone is using it because e0 gas is too hard to get. e0 would certainly be my preference, but I'm too lazy to drive across town and pay 15% more it. I go fetch e0 for the race car, but not for the DD which is an '88 BMW 535is so it's engine has a heck of a lot in common with our M20 engines.
Re. VR1. As was correctly pointed out in this thread, it's the NSL version of VR1 that is low on detergent. The NSL version is rarely available at the local autoparts store.
(1) This # comes from Jim Rowe@Metric Mechanic.
