quote:It might be informative to know WHY you'd wish to bump up the pressure with 10W-40. Racing? Towing? High mileage engine? Hot, arrid region? Just 'cause grampa and dad used it? Don't get me wrong - you probably have a valid reason, but, I also subscribe to the notion that the engineers who designed and nursed your engine through its development aren't idiots, either. (Unsure about the various car makers' marketing departments, though...) Also keep in mind that higher viscosity translates to greater pumping losses through the passages, bearings, and filter. Theoretically, at least, that results in less power and lower fuel efficiency. A healthy engine still within tolerance can maintain sufficient oil film strength even with lower viscosity fluids to "float" heavy bearing loads successfully. Ever skip stones off water? Finally keep in mind that 10W-40 has a higher "elastomeric" content than, say, 10W-30 oil. That means more viscosity index improver content in a quart (or, by extension less actual o-i-l). VIs do NOT lubricate - they only retard thinning from heat. The 10W-40 stuff HAS to have enough VI to cover a 30 point weight spread; the 10W-30, a more manageable 20 points. Since the VIs can be among the first components to oxidize off in hot (REALLY hot) operation, theoretically you could lose both volume and viscosity with the greater spread 10W-40 fluid. (The more VI you lose in 10W-40, the faster you get back to the original 10 weight base stock.) By the way, I'm NOT a mechanic or a lubrication engineer. This is all from "book learnin'" reading, not personal experience. Just a few points to ponder. -Ray Haeffele [ January 19, 2003, 10:34 PM: Message edited by: Ray H ]
Originally posted by higney85: o ok- sorry im a newbie when it comes to oil specs.. My main problem is the pressure after its been warm for a while.. so the 40w should bump up that pressure- correct?
quote:I don't think that's the way it works. A pour point depressant isn't going to affect viscosity or VI, it's only going to permit the oil to flow at lower temps. So, a 10w40 probably doesn't use a higher viscosity base fluid. The more standard route was for the 10w30 and 10w40 to use the same base fluid with the 10w40 having more VI improver to cover the spread. However, from what I've been able to read, modern 10w40s don't suffer from this malady as did the 10w40s of old. A higher VI base oil (say a Group II+ rather than a Group II, or Group II with a little bit of Group III) could be used and the amount of VI improver needed may be no more than what was required in the 10w30 using only a Group II base oil.
Originally posted by Dr. T: For the shear comments, the 10-40 should be more robust as it should have more of both VI's and Pour Point depressants which allow it to make the spread, all the while starting with a higher viscosity base oil, thereby not allowing for as much shear-back when used. At least this is my understanding.
quote:Yep, I am confident that the LT1 and LS1 would get better wear with a high 30/low 40wt oil. I'm not sure if I'd want a mid 40wt or higher though. But something in the 12-13cst at 100c range. I still don't believe there are too many engines out there which will actually see lower wear numbers with a 50wt oil though. But I will admit there are precious few 20w50 and 15w50 reports on here. I'd love to see someone do a comparison between a 20w50 and a 10w40 in their engine.
Originally posted by sprintman: On Saturday I changed from 10W30 w/Auto-Rx to Delvac 1 5W40 with approx 3/4 litre M1 0W40 TS added (leftovers) and reduction in general noise particularly in rocker area is very noticeable. First time I've used a CAFE viscosity oil (was the only straight dino I could find) and it will certainly be my last. Patman even you seem to agree LS1 need high end 30 or maybe 40 for reduced wear? IMO any 30 is not good and even more so if engine has a few miles on it.
quote:It shouldn't matter.
Originally posted by higney85: ooo before i forget.. When i swap filters can i go on and fill it back up to full using the 15w-40 or should i just use the 10w-30? Over this engine's lifetime it has had about 2 bottles of STP oil treatment and 2 bottles of STP stop leak and both did there job but i am wondering if these will all get cleared out. I used about 1/2 bottle of stop leak and oil treatment with an oil change so i didnt use too much i dont think. My oil leak always appears about 1500-2000 miles after the oil change and the leak is just enough to put i drip on the bottom of the bellhousing so its a small leak but id like to make sure everything is clear and the Auto-rx does its job and i can just run a good oil and filter and not haveta deal with it. Also what would be the best oil to run (the 15w-40 variety) thanx