Thicker vs thinner...

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Sep 20, 2003
AB, Canada
A Honda technician friend who does a fair bit of racing as well swears by the following for his Honda/Acura vehicles. ( All high-revving 4 cyl). M1 15W50 in the summer; M1 0W20 in the winter. He knows all about Honda and Ford's shift to xW20 year round; The dealer he works for uses only the recommended viscosities. He thinks otherwise, and when I asked him why, he said: 1) M1 15W50 is on the thin side of the 50 weight's not THAT thick. 2) You really need thick oil protection when its hot, and in stop and go traffic...BECAUSE stop and go means fairly heavy engine load when oil pressure is lowest and oil temps are highest. Near idle and with minimal cooling airflow. You don't have sufficient oil pressure at these low revs, so thicken up the oil to make up for it. 3) You NEED flow when it's cold. Getting the oil flowing to all critical engine parts is the MOST important aspect of winter oil. He also said that most of the time on cold winter days the oil never gets to its designed operating temp, so the thinner 20 weight is actually behaving more like a 30+ weight anyway...

Interesting comments from a Certified technician who seems to actually know something about oil...

I found the connection between engine speed and oil pressure to kind of make sense.

I disagree with him. He might know more about cars/racing then I do, but I do not think you need anything other then a 30wt oil in winter or summer. Too many high mileage cars with 30wt dino oils have proven this. I think a 40wt oil is ideal for racing in the summer months. As stated a billion times before, viscosity is one aspect of an oil and it really depends on what oil/engine your talking about.

1) M1 15W50 is on the thin side of the 50 weight's not THAT thick.

Mobil 1:

cSt 40*C - 125
cSt 100*C - 17.4
HTHS - 5.11

Looked it up, you are right, 17.4 just within the 50 wt. category. To me, that seem thick, but I use Amsoil 10W-30 and it is almost a 40 wt!
Your friend is "old school" and with old engines-it may be more applicable. Look at the UOA's with thinner 30 wts and 20 wt. oils. Lead numbers are frequently 0, 1, or max 2 for 3K miles and even higher miles for UOA.

Based on this site and observations I have made..thicker oils are just flat out not necessary with today's oil technology and engine loads. The other thing is that higher rpms demand a thinner oil due to classical bearing lubrication formulas.
I've read both sides of this issue about thick versus thin and the results of the thin UOAs speak for themselves. -but- Last year, I purchased a 2003 Crown Vic Sport. Cold starts on moderate days produced a 3/4 second knock, which is considered normal for today's "race start" engines. I switched from Motorcraft 5W-20 to Mob 1 0W-20. Now the knock was louder. I talked to the Ford dealer and they confirmed that this was normal and was not causing any wear. I also noticed that my father's GMC Denali has the start-up knock except it lasts for 20 seconds (Mob 1 5W-30).
One fact I left out. I drive a Crown Vic at work and we have a parking lot full of them (Police). Not a one has startup knock. What's the difference? They are all full of Delo 10W-30, and we haven't had an engine failure in 10 years. I talked with our fleet manager and he said the Ford has not tightened the internal specs on the 4.6 V-8, that the startup knock in the newer engines is due to the "race start" modes of the ECMs and thinner oils; another way to pass the newer emission standards.
Armed with this new knowledge, I switched to Chevron Supreme 10W-30 and the startup knock disappeared. Funny thing; my gas mileage improved.
We switched my dad's Denali from Mob 1 to Delo 15W-40. Amazingly, the startup knock was gone (mileage unchanged).
Maybe my conclusion is unscientific and like the Ford man said, the startup knock is not causing any damage, but I'll sleep better with the "thicker" 10W-30s.
I'm just gonna put my $.02 worths in,,,,,

My Ranger makes a start up knock and pinging, though it's quieted down since I switched to a different brand of gas, but that's another story.

I'm currently running M1 0w30 SS with just a smidge over 4000 on the oil and filter. The more I hear about Delo the more I want to try it. I think I'll stick with the reccomended viscosity and see how the truck acts. I feel like I'm robbing the thread, lol Then maybe afterwards Chevron Supreme. Delo and Supreme I see the most debated on this forum, but that's my opinion,,,,,AR
If this tech works at a good dealer he should have a lot of training . I would have to agree more than disagree with his knowledge.
If you're not educated in the engineering disciplines, there's still a lot of knowledge available to anyone willing to go to a library and look it up.

"Of the things that go into the design equations for fluid film bearings... oil viscosity is a major variable." Read, your bearings are designed for a specific MOFT and MPOP... that is, minimum oil film thickness and minimum profile oil pressure. Solid theoretical and empirical information on this can be found in Taylor, Charles, The Internal Combustion Engine in Theory and Practice. The M.I.T. Press, 1985. pg. 316-339
A competent and knowledgeable mechanic (I guess it's technician these days) has probably seen the inside of a lot of engines and can come up with some really useful opinions and information about oil and various grades, viscosities, etc. but when it comes to the hard core engineering and scientific methods employed by the tribologists and petroleum engineers at the PHD and higher level one quickly realizes that there is a lot more to this stuff than meets the eye. Throw in the politics of things like CAFE and environmental controls and you really are in head city. I don't think that even the best mechanics woud get past the first page of a PHD level text, (My apologies to those mechanics with a real engineering background). I don't want to come across as some kind of elitist snob but I have heard a lot of BS from people who should know better.
Vicosity is friction and friction is bad. The relationship among things like viscosity,shear resistance, load capacity, lubricity etc.etc. is a complicated one and what may seem obvious ain't necessarily so. You really have to do extensive testing and run the numbers to come up with anything meaningful. I guess thats what is really happening on this forum and eventually we will all find the best oil and grade for our individual rides. Question is ,once that has been determined, how much longer is your engine going to last with the most optimized oil as opposed to just using any old SAE approved slippery stuff.
Given reasonable service intervals, probably not much difference.

Originally posted by Motorbike:
Comments made by a actual Tribologist lead me to believe he is correct and obviously in the know of things .

I just can't win with you, can I?

All I'm saying is that I'm tired of people saying that thick oil is bad, and I'm tired of people saying that thin oil is bad. Both work.
Let's just cut to the chase: It simply doesn't matter. I've been on both sides of the fence in my lifetime, as have many in my family and among my friends. You know what? Run thin oil, and your engine will last at least 200,000 miles. Run thick oil, and your engine will last at least 200,000 miles -- if you keep the oil and filter changed and the level topped up.

I'm sorry, but the older I get, the more I realize that when it comes to oil, changing it regularly before it's trashed, and keeping the level up near the full mark are the most important factors. I would say that having an oil that flows well in winter is a close third, but you know what? Those in the family that are back on the farm still keep oil thick as molasses in their cars through Michigan winters and still routinely get over 185,000 miles on their engines with no trouble. **** , they rust out from underneath them long before they're worried about the engine. Repeat after me: It just doesn't matter .... How many engine failures that are lubrication-related are truly viscosity-related? In my experience, engines die when they're abused or ignored, not when a "too-thick" or "too-thin" oil is used. Is it smart to keep a 15w-40 oil in a 4-cylinder engine when it's 10 degrees out? No. But I know lots of people who do, and the cars keep going. My dad has insisted on 10w- or 15w-40 oils in all of his cars year-round in Chicago with not a spot of engine trouble whatsoever. Whenever I or anyone I've known has had major engine trouble, it's been becuase the oil and filter haven't been changed regularly, often, or enough, the oil level was ignored, there was a defect in manufacturing, or the engine just plain wore out after several hundred thousand miles.
Good post kev99sl! And given what you said, I say, why not cut the middle ground and run a quality 10w30 or 10w40 and forget the rest (unless you live in the Artic)?
I think that what Kev said is basically true for the average person, however if you drive extremely hard, viscosity becomes much more important.

If you drive very hard and you're running an oil that is too thin to begin with, plus you add on top of that the higher oil temps (thinning the oil out even more) that is a recipe for shorter engine life.

I'm not saying people should all go out and run 15w50 if they drive hard, but for a lot of people they would find a thick 30 to thin 40wt is better suited for them.

As usual, every engine is different though, so UOAs become important.
When in doubt I'd rather err on the side of more protection. Given my driving style that means I lean towards thicker oils that are specified for my engine. Having a car with an oil pump capable of putting out 200psi, I don't see the need for very thin oil. I think flow will be just fine, even if a 20W-50 or 10W-60 is used (I don't live in the Arctic circle).
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