Oil has a difficult job to perform. At startup, even at very low temperatures, it has to flow rapidly to protect the bearings and cylinder walls. Then, after warmup, it has to keep protecting those surfaces with out evaporating or burning off.
Today’s cars run hotter, and still only use 5 quarts in a 300+ hp engine.
A modern multigrade synthetic will flow at -50F and still be able to protect turbocharger bearings at high engine loads. For that, of course you need something like a premium 0W40, or 5W50. You cannot formulate this spec with normal mineral oil. Many European cars with turbos specify these premium oils!
So, for a typical 4 cylinder non-turbo econobox, 5W20 mineral oil will still suffice, but don’t go towing a trailer with it. For that you’d upgrade to 5W30.
Engine gaskets and seals have improved as have oil control rings. I now find that on my 5 year old Toyota with 5W20 mineral oil I sometimes use, I can’t add any oil at 5000 miles!
My point about the transmission is that they’re mass produced and machined on a jig. The mainshaft assembly drops into place and the bearings are located by dowel pins. There is of course slop lengthwise in the shaft. Subaru offers about 10 different 3/4 shift forks (same on 1/2) that are numbered.
The ends of the fork where it fits in the synchronizer sleeve is machined with an offset. There are about 5 forks machined one direction and 5 forks going the other. The measurements must be taken on the synchronzier assembly and gear sets and the sleeve centered. This means the sleeve is held in the proper place by the fork and that is done by selecting the proper fork.
If the machining was dead on there would be no need for 10 different shift forks and going through the procedure of picking the right one. (I would add that this is not a matter of .0002 or something like that. We’re talking .020, .030, and so on.
As I said, I do understand your point and agree about the machining accuracy but do not agree that it makes any difference on engine longevity. Example, and say the oil clearance is given as .001 - .0024.
Assume one engine has journals all at .002 and another has a tighter fit with all journals at .0016. Does that mean the latter will be a better motor because of that .0004? No.
Regarding heavyweight oil I don’t necessarily consider it the kiss of death on an engine. When my cars reach high mileage I usually run 20/50 in the summer and have done this for decades with no problem. My old Mercury had a diet of 20/50 for about 250k miles after it reached the 150k mark.
At some point there is enough wear on the bearings and journals that a heavy oil can help keep those bearings seated on the rods. With thin oil and enough wear it’s not unheard of for a rod bearing to swap sides and cause a catastrophic engine failure.
Would I use 20/50 in a low miles motor? No, but there can be a place for it later on.
Same goes for my motorcycles although that veers off into the air cooled thing. My HDs run the factory recommended straight 60 weight although I do not use the overpriced HD branded oil.
I run 60 weight Aero Shell, which is an oil used in aircraft engines.
Again, I apologize if I come across as combative. It’s not meant that way at all,
It’s hard to venture a guess without fully understanding the design but sometimes tolerance stack up on complex mechanical parts and the way they interact is best solved in this way. Remember that the final solution the mechanic sees is always a compromise in various factors almost always heavily weighted toward total cost.
There’s a big difference between purely technical and financially viable solutions.
I understand your perspective also. I didn’t interpret your responses as combative, just an honest debate on a point of which our perspectives are different, that point being the effect of modern manufacturing practices and their better consistancy on engine longevity. I enjoy these discussions and learn a great deal from them. Sometimes I change or question my beliefs because of them, and that’s healty. Having been inable to find the data that I thight I’d remembered reading about different driveshaft lengths ultimately being used as a solution to torque steer (not to be confused with the excessively different lengths having caused it when FWD first became unbiquotous), I’ve come to question my belief on that issue.
I’ve always believed that intelligent, educated people will not always agree, and often both have good, valid reasons why they believe as they do. That’s healthy. The moment that stops is the moment one of them has stopped thinking for him/herself.
I did, however, want to be sure that nobody interpreted my commenst as having originated in doubts of the ability of machinsts and toolmakers to do what they do with precision and accuracy. I’ve seen machinsts that I know create things that boggle my mind, occasionally out of materials the I’d never think were workable. I have only the utmost respect for skilled craftsmen/women of all fields, including machining.
Heavyweight oils have their place for certain, but not for the average driver on his daily vehicle…unless he’s nursing a tired old motor. It bothers me to hear of people who don;t even know what oil does trying weights different than those recommended by the manufacturers. You using a different base weight is not the same as the wverage person using a differnt base weight. You know exactly why, what you’re trying to accomplish, what the oil is doing, and what to watch for. The average person doesn’t.
We’re good. And perhaps someone following along has learned something from the discussion. Iknow I have.
This discussion has been repeated on this and other boards hundreds of times…
20-20W was a popular weight of motor oil 60 years ago and it still is…The only thing to have changed is the lubricants ability to flow at very low temperatures…Now we have 0-20 rated motor oil…The oil doesn’t thicken up as much when it’s cold…End of story…
Machining? Pistons may be machined - but any more they electron beam clad the cylnder walls so precisely that no further machining is necessary. Just hone and go. Heck I think the rings are almost zero gap and dont require any additional fitting because of such processes. Its not just machining, the whole process has changed.
Also - this is an high compression engine. (10-1 or something) It also has direction injection. It has variable valve timing (which may be electronic and may be hydrualic - YOUR MOTOR OIL - thicker may mess up your VVT.)
It was designed and tested by toyota on some machine for 1000’s of hours at full throttle with 0-20. I would just use what they used.
Ring gap minimized today primarily to reduce crevice volume. You can buy similar type rings (overlap) for legacy applications but for the purpose of maximizing VE. However, your points are well taken.
