oil weights?

It's not just CAFE stamdards, or bearing tolerances. Most modern cars have some sort of Variable valve timing, in which viscosity makes a MAJOR difference in proper operation.

alfadriver wrote: Who cares if it's about CAFE- how many posts here are about us (the entire industry) ignoring fuel economy- so here's one that keeps it in mind, and now it's bad all of a sudden? BTW, thicker oil will be a problem in colder temps. Just sayin. (pressure does not always mean more flow- usually means less)

Actually, I care about fuel economy. Unfortunately, not many others do and so we see 15 mpg SUV's doing commuter duty with one person aboard. I would like to see car buyers demand more fuel-efficient vehicles, but that's not likely to happen unless gasoline prices head back north of $4. a gallon. What I don't want to see manufacturers doing is compromising engine life by recommending thinner oils to squeeze out a fraction of an MPG.

Summer here saw two months of temperatures well above normal. I think we had a couple weeks where the high was 105 or near that. I might choose to run 5w20 in the winter, but over 100 deg. F? I'm sorry, but that contradicts everything I learned in Tribology class. And I double-checked my owners manual--5W20 is the only recommended oil, for all temperature ranges.

1988RedT2 wrote: Actually, I care about fuel economy.

So now I'm confused- you say you care about fuel economy, but when we in the auto industry use thinner oil to help fuel economy that is part of the CAFE requirement- it's bad??? Lost me there.

What I don't want to see manufacturers doing is compromising engine life by recommending thinner oils to squeeze out a fraction of an MPG.

You keep saying that, and I have still yet to see data that there's a rash of engine failures due to oil viscosity withing 50k or 5 years of the end of your factory warantee. By rash, I would say that 1 in 100 would be significant. Or R/1000 of just 10 due to oil flow problems.

One never hears of engine failures due to too thin of oil. I've heard of engine failures in Toyota's that are from oil sludging... maybe that is your reference? But pre-mature engine failures due to internal wear? No. Heck, I'm still runnig the 10W30 in my Miata, barely meet the 5k oil change (ususlly 7.5-10k), and have 176k miles. That's more than 100k past the factory warantee and almost 100k past the emissions hardware warantee.

So, find me the data that show 1% failures due to oil that is specified too thin.

I experimented with light oil in my Supra earlier this year. German Castrol 0w-30, It had good oil pressure before and was in good running condition. It didn't last very long with 0w oil, spun a rod bearing on the 3rd run of the first autox I took it to after the change.

tuna55 wrote: I think you missed the point. I meant that it isn't as if all old engines had huge bearing clearances. That is not the driving factor when it comes to oil weights as judges by those two polar opposite examples.

The small-block Chevy is a fairly modern engine, as things go. The only old-timey thing I can think about it is that the first examples didn't have full flow oil filters, and as a side effect, all SBCs send unfiltered oil to the rear main. That's why they always look like garbage compared to the rest.

alfadriver wrote: So now I'm confused- you say you care about fuel economy, but when we in the auto industry use thinner oil to help fuel economy that is part of the CAFE requirement- it's bad??? Lost me there.

It costs more fuel to build a new car (or rebuild an engine) than you lose by not using the ultrathin oil.

Knurled wrote:

tuna55 wrote: I think you missed the point. I meant that it isn't as if all old engines had huge bearing clearances. That is not the driving factor when it comes to oil weights as judges by those two polar opposite examples.

The small-block Chevy is a fairly modern engine, as things go. The only old-timey thing I can think about it is that the first examples didn't have full flow oil filters, and as a side effect, all SBCs send unfiltered oil to the rear main. That's why they always look like garbage compared to the rest.

A Packard I8 has a bearing clearance of 0.001-0.003. Not all that different. Old enough for you?

Knurled wrote:

alfadriver wrote: So now I'm confused- you say you care about fuel economy, but when we in the auto industry use thinner oil to help fuel economy that is part of the CAFE requirement- it's bad??? Lost me there.

It costs more fuel to build a new car (or rebuild an engine) than you lose by not using the ultrathin oil.

Again, data. I would really like to see any actual evidence that engine life spans are shorter than the general vehicle so that the vehicle is scrapped because of the thin oil spec or the engine needs rebuilt due to the thin oil spec.

Otherwise, you are all posting- coudla, woulda, shoulda thoughts.

If engines fail, yes, you are right. But engines are not failing.

In reply to alfadriver:

I think somebody just used a perfect example of their engine failing. Now, it could be extreme coincidence, but I don't believe in coincidence.

HiTempguy wrote: In reply to alfadriver: I think somebody just used a perfect example of their engine failing. Now, it could be extreme coincidence, but I don't believe in coincidence.

Uh, no, they didn't.

That was an example of someone posting that they experimented with an oil thinner than spec, and it failed. That's not anything of what I am saying. I would never put a thinner spec oil in and old engine that needed thicker oil.

Stick with what is specified, and if it's specified as 0w20, then it will be fine.

If you put 5w30 into an engine that is asking for 10W40 or thicker, that's not the same.

The 350hp twin turbo V6 that I worked on was specified as 5W20, and it was beaten up to make sure it will survive. The odds of it failing due to the 5w20 being too thin are very small.

In reply to alfadriver:

My mistake. I had thought those specs might have been for his car and he was simply running the lighter oil choice.

alfadriver wrote:

HiTempguy wrote: In reply to alfadriver: I think somebody just used a perfect example of their engine failing. Now, it could be extreme coincidence, but I don't believe in coincidence.

Uh, no, they didn't. That was an example of someone posting that they experimented with an oil thinner than spec, and it failed. That's not anything of what I am saying. I would never put a thinner spec oil in and old engine that needed thicker oil. Stick with what is specified, and if it's specified as 0w20, then it will be fine. If you put 5w30 into an engine that is asking for 10W40 or thicker, that's not the same. The 350hp twin turbo V6 that I worked on was specified as 5W20, and it was beaten up to make sure it will survive. The odds of it failing due to the 5w20 being too thin are very small.

Thanks for the posts, I value the professional info. A related question if you don't mind: Do you think some manufacturers get carried away with extended oil change intervals a few years back at the expense of engine longevity?

Shaun wrote: Thanks for the posts, I value the professional info. A related question if you don't mind: Do you think some manufacturers get carried away with extended oil change intervals a few years back at the expense of engine longevity?

Still debating that. there's pretty strong desire from customers to have 10k oil changes. Oddly enough, the demand started in Europe.

But I think engine technology is advancing enough that oil dillution, blow by, etc- are being controlled enough to allow the oil to survive 10k miles over the life of the vehicle.

The side benefit- the less oil that is burnt, the better the emissions over the life of the car.

It may have been premature, but the days of 10k oil changes with reasonable usage is here. More importantly, there are enough indicators in the oil that the oil life measurements that you see on the dash are getting better, and more relevant.

Even with all that- for most engines, they can take a lot of abuse that will make them last longer than the body/chassis.