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Ecky 02-15-2017 12:50 PM

Blackstone newsletter - Can You Use a Thinner Viscosity Oil?


Viscosity: Going Down!
by Ryan Stark

April of 2017 will mark my 20th year here at Blackstone and in that time a lot of changes have taken place. I’m a big fan of change myself. Long ago I got some advice from my Uncle Dan who said, “The only thing that’s constant in life is change.” I decided that his words were the truth, and it seems to me like change should be embraced because there is no stopping it, and also for the most part change is good. It might not seem good at the outset, but if you give it some time, things eventually work out. After a bit of reflection on the changes in the oil industry, I’ve decided that one of the best ones has been the trend to lower viscosity oils.

The thin oil trend
I started changing my own oil on a regular basis in the early ’90s, and at that time 10W/30 was the oil of choice in my 1981 Chevy Citation. I didn’t think that much about it. It said right on the oil cap use 10W/30, so I bought whatever was on sale and went along fat, dumb, and happy. At that time 5W/30 oil was starting to be as common as 10W/30 on the shelves, but I never went with it because it wasn’t what GM said to use. However, my wife’s first car (1994 Buick Skylark) recommended 5W/30, so that was a sign that thinner oils were starting to come into favor. Again, I didn’t think much about it, and basically just stuck with what was recommended when I changed her oil. Then, in the early 2000s I noticed that we were starting to see a lot of samples from Ford V-8 engines that were running 5W/20 oil. This was a bit of a surprise since that’s pretty thin oil, but it was hard to argue with the results. Those engines produced some of the best wear we would see on a regular basis, so it quickly became obvious to me that this was a change for the better. And if you think about it, it makes sense.

Wear at start-up
For years, it was taken as fact by a lot of people that most of the wear in an engine happens at start-up. Now I haven’t done any studies myself to see if that was true, but that statement didn’t seem out of line from what I know about engines. So assuming it’s true, why would just starting an engine cause wear? Well, I believe the answer is the oil isn’t flowing over all of the parts like it does shortly after start-up. I do know that engines have virtually no metals parts touching one another without a thin film of oil providing a lubrication barrier, at least once oil pressure has been established. I also know that thin oil pumps easier than thick oil, so it seems obvious that the quicker you can get the oil to the parts, the less wear an engine will produce. From then on I was sold on thin oil.

So what’s the problem here? Well, when I first started at Blackstone, I was told that thick oil is good for the bearings, and I didn’t have cause to doubt that statement until I saw these Ford V-8s producing virtually no wear, and I knew some of them were work trucks that were hauling heavy loads. So could it be that the bearings didn’t need thick oil to survive? The answer is a resounding yes.

Even for diesels?
That trend toward thinner oil has proven true everywhere except for diesel engines. For years and years and even today, the oil of choice in a diesel has been 15W/40. But, if a heavy-duty gas engine can run light oil, why can’t a diesel? We would occasionally see diesel samples from Alaska that were running 5W/30 and they would look fine, so why not use it down here in the lower 48? In colder weather, it was acceptable for diesel to run thin oil, but that really only matters on start-up. But the oil doesn’t get thicker as it heats up -- it thins out. So could it be that thin oil does fine even when it get gets up to operating temperature? The answer to me was another resounding yes, and I wondered when the day would come that 15W/40 would no longer be the manufacturer’s choice for diesel engines. Well, that time has come!

Today we are starting to see more diesel fleets going to 10W/30, and I’m here to tell you that this change is good. Not only will the bearings do just fine, but the engines will start up better (especially in the cold). And this change might eliminate the need for plugging your diesel in at night. Now, there will always be some people who are resistant to change. In fact there are whole countries that are. The German vehicle manufacturers have yet to embrace thin oil, though I think that change will happen some day.

Not really a technical article, but the timing was interesting, given I've only just started to become interested in thin oils myself.

oil pan 4 02-15-2017 01:02 PM

This is one of the reasons why I went to roller cam and full roller rockers on my 489 build.
Not just use thinner oil but also oil with fewer additives like SN or SM rated oils. Instead of 1980s and 1990s SH and SJ rated oils.

ThermionicScott 02-15-2017 02:22 PM

Good stuff! Interestingly, the trend toward thinner oils seems like a return to me. Many cars used to specify SAE 20 oil when ambient temps were between freezing and 100F or so, so they must have thought it was adequate when the engine was up to operating temp.

VW in particular spec'd SAE 20 until about 1966, and oil temps were a little higher in those engines compared to water-cooled engines of the day. It seems that in the time since, there was a trend toward thicker and thicker oils in the belief that they provided more cushioning for the bearings, especially in hotter-running engines. So you'd see SAE 30, 40, 50, even 60.

It's good to see that sense has returned! Start-up wear is what we should be concerned with, and as long as the oil pump can maintain adequate pressure, and the oil has adequate anti-scuffing additives, why not go thinner? :) In fact, aircooled VW fans often cause themselves a lot of trouble with thick oil, because the extra pressure causes oil to bypass the cooler, and it runs hotter as a result.

There was a guy on BITOG that ran his otherwise-stock Jeep on 0W10 and still got great wear numbers.

BTW, Ecky, you might want to trim your quote back to a couple sentences. I think copyright laws usually allow for quoted summaries, but frown on reproducing whole pieces.

MobilOne 02-16-2017 01:35 PM

My experience with 10w40 Mobil One synthetic is that I get many miles of use out of my engines. 200k miles on my 2001 Silverado, 320k miles on my wife's 1999 Avalon (so far). I change the oil and filters at 4000 miles. I've tried 5w-20 in the truck and the lifters rattled a lot; so I changed that out after 1000 miles. Now, I live near Atlanta, so it doesn't get as cold here as some places. If I still lived in Michigan, you can bet that I would use a thinner oil. And if I had new cars I would use a thinner oil.

Years ago, I used to see advertised an electric auxiliary oil pump that was used to circulate the oil prior to starting the engine. If I lived in a cold climate, I would look for one of those.

oil pan 4 02-16-2017 03:16 PM

No reason to circulate cold oil unless it can be heated.

Hersbird 02-17-2017 12:07 AM

I'm debating using something besides 15W/40 in my Cummins. Does anybody here have any experience? I know I need to find something rated to handle the soot and my motor has 273K on it. Would that make it potentially worse or better to use a thinner oil? Some people use a 5w/40 synthetic but that seems like a big spread in viscosity to me.

Ecky 02-17-2017 06:26 AM

Oils with a thinner winter weight will gradually get thicker when cold as the viscosity modifiers break down. A 5w40 will not be 5w anymore after a few thousand miles.

RedDevil 02-17-2017 08:31 AM


Originally Posted by oil pan 4 (Post 534505)
No reason to circulate cold oil unless it can be heated.

I think the aim of the auxiliary pump is to get oil where there is none (overhead cams etc.) before the engine starts. There will probably be some residual film or whatever, but you cannot be sure it will last until the oil reaches it.

A thinner oil will reach those parts faster than a thick oil, but if the pump runs before the engine does those would be lubed immediately.

ThermionicScott 02-17-2017 11:14 AM


Originally Posted by Hersbird (Post 534526)
I'm debating using something besides 15W/40 in my Cummins. Does anybody here have any experience? I know I need to find something rated to handle the soot and my motor has 273K on it. Would that make it potentially worse or better to use a thinner oil? Some people use a 5w/40 synthetic but that seems like a big spread in viscosity to me.

I've used 5W40 and 0W40 with no issues in gasoline engines. From what I've gathered, the Rotella T 5W40 is all Group III, so it doesn't need as many VIIs as a dino version would. I would be surprised if 0W40 didn't involve some Group IV/V to reliably get its viscosity spread.

Hersbird 02-17-2017 12:00 PM

I'm specifically wondering about the 10w/30 in diesels the article mentions. I was going to go 5w/40 synthetic but wonder if 10w/30 might be better. I'm not going to be towing more than 1/2 the truck's rating and I'm not the type to power up a hill at 75mpg towing just because the truck can do it.

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