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09-21-2015, 11:42 PM | #1 |
Captain Fatbelly
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Thin oil and hydraulic lifters
So several months ago I switched from 10/60 to 5/40. After the switch I was pleased with how rev happy it was, but the car seemed to have lost a little punch, which bothered me as I expected the opposite. I looked around here and discovered that although the majority felt that their car seemed quicker on 0w40, several people had the same feeling I did, that the car just didn't seem as stout after the change. Of course they were promptly told they were wrong, thinner oil equals more power, placebo effect, etc, but after doing some research on my next oil recently I came across this on the corvette forum which got me thinking about it again:
"Thinner oil will typically increase HP because of less viscous drag and reduced pumping losses, compared to thicker oils. That is why very serious Race efforts will generally use watery thin oils in their engines. But, an exception to this increase in HP would be in high rpm hydraulic lifter engines, where thinner oil can allow the lifters to bleed-off at higher rpm." That's a small part of a very good write up that can be found here: http://www.corvetteforum.com/forums/...0-vs-0w30.html But that got me wondering if possibly this can happen with our high rpm hydraulic lifter s65 engine? Anyone have any knowledge on the subject? Could bmw have spec'd the 10/60 for this reason? I'm posting this because I'm trying to find a mechanical reason why my car seemed to lose something when I switched to the 5/40, which mechanically doesn't make a lot of sense. Any input welcome.
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09-22-2015, 12:19 AM | #2 |
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I switched to motul 5w40 about 600 miles ago from 10w60, car is much smoother etc. Can't say I have noticed any loss in power at all though. Im supercharged so this may be affecting that but shes pulling just as strong as ever.
Do love how the car feels with the 5w40 though, so even if I was loosing a tad of power I would still keep it. Pending blackstone report that is
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09-22-2015, 03:56 AM | #3 |
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Your engine lost nothing with the 5W40, it is still a 40W at operating temperature. Do back to back dynos and then we can talk. Until then, you are just buying into a myth, the oil is not getting pushed out of the lifters at high RPM. The amount of HP gain/loss from oil is negligible at best. Besides, the S65 is rev happy even with the 10W60.
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09-22-2015, 08:32 AM | #5 | |
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09-22-2015, 09:48 AM | #6 |
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Doc,
I've dyno'ed my car with M1 0W40, the chart looks like any other chart from Dynojet, the engine makes power all the way to redline, flat torque curve after 2500rpm or so. My car made 357hp/262ft-lb on a 104F day here in So. Cal. I keep on telling myself with a tune/test pipe/lower temperature, my car could be pushing 400whp!! |
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09-22-2015, 10:14 AM | #8 | |
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Last edited by Doc Oc; 09-22-2015 at 10:24 AM.. |
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09-22-2015, 10:37 AM | #10 |
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Yeah, it does make it difficult to tell. Not sure if its anything at all. I was comparing to this:
Last edited by Doc Oc; 09-22-2015 at 10:42 AM.. |
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09-22-2015, 11:43 AM | #12 |
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Probably has more to do with mods than anything.......but the car was designed for using a 1060 with a vis @ 100c of around 21 wheras a 0w40 is in the high 12's to low 14's (except redline which is 15.6 and what I'm considering switching to). That's a helluva difference there. And if a large drop in viscosity does/could cause lifter bleed off you'd expect it to happen in that rpm range. I have no idea what effect that'd have on the powerband though and it's really pointless to speculate without a before dyno on 1060.
Last edited by Doc Oc; 09-22-2015 at 12:24 PM.. |
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09-22-2015, 12:52 PM | #13 |
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Maybe the Porsche engineers will learn from this thread. They spec 0W40 for the GT3 that revs to 9000 and uses hydraulic lifters.
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09-22-2015, 01:03 PM | #14 |
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09-22-2015, 02:07 PM | #15 |
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It's interesting the usual suspects arrive and dismiss the thought by the OP with no objective or thoughtful response. Just like bearing clearance is a tgeory, why not consider reasons bmw actually chose 10w60. I pointed out another which also was scoffed at.
1. Vanos relies on oil pressure to operate.accurately. 2. Lifters rely on oil pressure. Why would changing oil not impact these things and many others? |
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09-22-2015, 02:12 PM | #16 |
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In fairness , it's oil pressure that matters so size of oil channels, bearing clearance, oil pump used all totally dictate oil pressure in addition to oil. So you can't make a blanket comparison since Porsche species that oil, they obviously ensured it provided optimus pressure
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09-22-2015, 02:36 PM | #17 |
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Here's the thing: Porsche didn't originally spec 10w60 for the GT3 and then the Porsche community decided to go 0w40 (against porsche recommendations) so I don't see a correlation. I'd be shocked if the factory spec'd oil wasn't the best choice for the GT3. I'm sure the engine is designed and tested with 0w40 in mind. However, that really has no bearing on what happens at 8000 rpm in the s65 when you reduce the recommended viscosity by 30%. Some data on that would be nice. In 8 years has no one ever dyno'd the same car, same day with different viscosity oil? Any other kind of tests?
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09-22-2015, 02:39 PM | #18 | |
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09-22-2015, 03:04 PM | #19 |
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If other car enthusiasts had documented this sort of issue on a wide scale, I would bite. But they have not as far as I can tell. Honda and Porsche both run thin oil in high rpm hydraulic lifter motors without issue.
I have noticed some dynos flattening out on the top end and always assumed it was misfire or timing related -- old plugs or weak coils or fuel octane that did not allow maximum timing. Maybe the OP is onto a discovery, but I'll wait for conclusive dyno testing before changing from 0W40 to 10W60. |
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09-22-2015, 03:27 PM | #20 | |
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Keep in mind that all of this is conjecture on my part. I dropped viscosity, noticed a difference, and have been curious since. I'd all but decided it really was in my head until I stumbled on the article I quoted in the first post. That was the first thing I'd ever read that mentioned the lifter bleed/thin oil connection....and of course I immediately thought "hey, I have a high revving hydraulic lifter engine that experienced a change in power and after going thin". I could be completely wrong and am certainly not married to the idea, but the fact that no one has done much research into the effects of drastically reducing the oil viscosity on the s65 is puzzling. Last edited by Doc Oc; 09-22-2015 at 04:03 PM.. |
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09-22-2015, 04:16 PM | #21 |
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If I was losing 20 rwhp due to valve float from collapsing lifters up top, I would put 10W60 back in rather than try a compromise oil that might lose only 10 rwhp up top.
My understanding is that a year or two ago the engineers at BMW revised the oil spec for the S65 to include any weight LL-01 rated oil such as Mobil 1 0W40, Castrol 10W60, and Castrol Edge Professional 5w30. I assume BMW would not have revised the spec to include lighter weight oils if it could result in valve float |
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09-22-2015, 04:24 PM | #22 |
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That supposed document was nothing more than an error in labelling. At no time as bmw approved anything but 10w60 for use other than emergency top offs with a lower weight.
Again, you can't say any hydraulic lifter engine is the same. It's oil pressure that is key so if an engine is designed with a grade to begin with, the design would incorporate the oil pressure they targeted We are changing oil pressure in an engine not designed for it. Whether it matters who knows |
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