Why go heavier?

[dragboat]

Someone needs to email those salemboys the virgin test of the Valvoline and tell them of GF3.

Still many different uses for a heavier oil on the street. Towing long distance with a gas motor,taking trips like we use to non stop to California,Wyoming ect where mph got pretty high at times in cars without automatic overdrive transmissions ect.Then the old hotrods with big cams and heavy springs,and can't forget those heavily modded mowers

Times they are a changing for old Dragboat though,getting very close to sticking some Synthetic in the newest car in the Family Fleet. Make this new technology work for me and stay out from under it changing oil so often and possibly gain enough gas milaege to offset the cost over the next 200K or so
We run them in the ground as well,only one car left we have that has a carb on it

 

[csandste]

"Someone needs to email those salemboys the virgin test of the Valvoline and tell them of GF3."

Obviously it's not so important to them they're going back in to their previously posted FAQ's and do that. Mark Salem is a very good mechanic, but I bet most of the posters on this site know more about oil then he does. However, look at the number of FAQ's he maintains. Cars are extremely complex things, with all sorts of areas that can go wrong. We all go nuts finding the best possible oil, but there's hundreds of other ailments that can scrap old bessie other than engine failure. That's why I'm not big on synthetic.

Truth be told, most of us need to get a life. There's thousands of cars out there with hundreds of thousands of miles and owners who go with Pennzoil 10W30 because that's Grampa told them when they were ten years old. Truth be told, if they change at 5000 mile intervals they'll probably sell the heap because they finally get tired of it or because the air conditioning compressor gives out for the second time, or the power steering pump needs replacement.

In the meantime, I like this site because I learn all sorts of arcane facts about lubricating. You've got to admit though that we're all probably a little weird on this subject.

 

[csandste]

My apologies. I've gone 57 years without using the term "truth be told", which is meaningless and fogey-like and I just used it twice in one paragraph.

Excuse me while I drool down the front of my shirt....

 

[Patman]

I agree, we are wierd!

All the time I hear about someone who has 200 or 300k on their car, and has used nothing but the cheapo oil on special, changed every 3k. It's hard to convince someone like that of what we do on here (longer intervals, more expensive oils, etc.)

However that doesn't mean what we are doing is wrong. It's just that we sometimes do worry a bit too much. I'm guilty myself.

 

[satterfi]

Ken

Good point on 10w40 vs 10w30 dino oil. I forget people still buy that stuff.

My point of view comes from using a group 5 10w40 and when someone tells me a 10w30 is better I have my doubts.

The engine that I have that recommendes 10w40 has main journal bearing clearances of .0008-.0015 inches. It redlines at 10,200 rpm.

What are the clearances of the engines the spec 30 and 20 weight oils and what is the max rpm?

 

[MolaKule]

"In the meantime, I like this site because I learn all sorts of arcane facts about lubricating. You've got to admit though that we're all probably a little weird on this subject."

We're weird, but we love it!

Keeps us out of the kitchen and away from the dishes, ain't that good enough??

 

[MolaKule]

"Then the old hotrods with big cams and heavy springs,and can't forget those heavily modded mowers Times they are a changing for old Dragboat though,getting very close to sticking some Synthetic in the newest car in the Family Fleet. Make this new technology work for me and stay out from under it changing oil so often and possibly gain enough gas milaege to offset the cost over the next 200K or so
We run them in the ground as well,only one car left we have that has a carb on it"

Dragboat,

You know when you "have arrived" when you put synthetics in your lawn mowers!

 

[TooSlick]

Bob,

I agree with you 100% ...I think running a 15w-40 diesel oil in an engine designed for a 5w-30/10w-30 does not make lots of technical sense. This is paticularly true in cold weather, when you want the oil to flow well during startup/warmup. A fair amount of your engine wear takes place during this period, especially in short trip driving.

What you want to achieve is optimium oil pressure, regardless of the ambient temps. As long as you are seeing 15-25 psi/1000 rpms of engine speed, you aren't going to have issues with bearing wear. At that point the efficiency of your air/oil filters is more important in preventing wear.

If your oil pressure is marginal or oil consumption is high, only then does it make sense to go up an SAE grade in oil selection. Even then I'd probably only do it in warm weather ....

TooSlick

 

[jason07-1zzfe]

quote:

---

Originally posted by Patman:
I agree, we are wierd!

All the time I hear about someone who has 200 or 300k on their car, and has used nothing but the cheapo oil on special, changed every 3k. It's hard to convince someone like that of what we do on here (longer intervals, more expensive oils, etc.)

However that doesn't mean what we are doing is wrong. It's just that we sometimes do worry a bit too much. I'm guilty myself.

---

I agree, yes anybody can make a car last that long with just about any oil with changes every 3k. But in what condition is the motor? Yeah it runs. But that is not good enough for me. I want it to still be just about the same condition and with the same power it came off the assembly line with (if not more power due to break-in). AND be that way while taking the constant abuse I give it, also without having to change the oil every month or two. I think my car was that way when I bought it (thanks to exclusive use of 15w40 and 20w50 of the previous owner). So that is why I have been using synthetics (M1 and now Red Line since I have wised up

) for those past 50k miles.
My car has ran a 15.49 in the 1/4, which is .01 faster than magazines tested them at when new. And that was in 90+F and humid weather, uncorrected time. So I want to keep it that way for the next 163k++ miles. And I refuse to take it easy on the car to make that happen

 

[Patman]

Good point Jason! A lot of these guys that get 300k out of their cars are driving them like little old ladys. Those of us that flog our cars hard are probably a lot better off going with the premium oils. Plus we can sleep better at night knowing we are doing things right, and not having to crawl under the car every 3k.

 

[Chris A]

quote:

---

Originally posted by TooSlick:
Bob,

As long as you are seeing 15-25 psi/1000 rpms of engine speed, you aren't going to have issues with bearing wear. At that point the efficiency of your air/oil filters is more important in preventing wear.

---

Isn't that a little high? I've always heard 10 psi/1000 rpms. With the 15-25 rule, at 6000 RPM, you would need 90 - 150 psi of pressure. I don't think any stock engines get there.

 

[Patman]

I've often heard the 10psi per 1000rpm rule too, but my LT1 has an idle oil pressure of about 18-20psi, and that's with a low 600rpm idle in drive. At 2500rpm I run about 40psi of pressure. I noticed similar readings with my previous LS1 and LT1 f-bodies too.

 

[MolaKule]

One minor point - if one is using an oil which has a good boundary lube that has left a coating of AW film, why worry about cold startup with the thicker oils of say 10W30, 10W40, or even 15W40?

My view is that 20W50 and higher viscosities are for large clearance racing engines that need thicker films.

Thicker, thinner, is relative of course, but today I think we see 5W20 and 5W30 as thinner oils, verses the old standby's of 10W30, 10W40, and now even 5W40 and 15W40.

As I have stated before, a one step increase in viscosity grade only gets you about 1.5 um increase in film thickness (60 millionths of an inch), according to actual on-car tests.

 

[MolaKule]

There are other considerations as well, such as load, rpm, bearing diameters, viscous friction, and heat dissipation. The thinner the oil, the less the less time the the oil stays in the bearing; the heavier the oil, the more power you are going to waste in shearing the oil layers.

Yes, you could probably use a thicker oil, but the heat rise in the bearings might prevent that.

The point of the previous post was to point out that slightly thicker oils might not flow as fast in cold temps as thinner oils, but if the oil has good barrier AW additives, then the thicker films would be advantageous for hot engine operation. This is why I maintain that 10W30 is the best general viscosity for economy of operation, temperature control, low VII's, and film thickness.

 

[MolaKule]

If you go to the Interesting Articles section and examine the article on Bearings and FIltration, I made the following statement regarding the design crtieria for bearings, "...Ho is the “Minimum Film Thickness.” So how does one find the viscosity required for a bearing? One uses the
“McKee” equation, along with the “Lasche” equation, for bearing heat generation and dissipation, Hd and Hg, and equates these equations to find the viscosity required!"

The two heat equations mentioned are set equal to each other and the variable to be solved is the viscosity. The other variables are load, diametral clearance, coefficient of friction of the bearing or surface, and the max temp of the bearing surface. So, many variables (considerations) are used to determine viscosity, with temp rise as one of the major considerations. Also recall, that the higher the viscosity, the more HP goes into churning the oil, and the more HP put into the oil, the higher the temperature of the oil.

Example. A journal bearing 3" long is supporting a load of 1645 lbs. on a 2" diameter journal bearing turning at 750 rpm, with diametral clearance of 0.00273". What should the viscosity of the oil be in centipoise if the operating temperature of the bearing surface is to be limited to 170 F?

Setting Hd to Hg (heat generated to heat dissipated) and solving for viscosity yields a vis. of 10.45 centipoise or SAE 20 weight (at 170 F). Now increase load and rpm, and the required viscosity will be higher. Now, what an engineer will do is run a number of analysis for temps, load, rpms, different clearances, and then use highest and lowest values of these variables, and then make a determination of the required viscosity or viscosity range for the engine.

Now enter CAFE. The engineer might want to specify a 10W30 or 10W40 because of the bearing temps likely to be encountered, but in order to squeeze out a measely 0.1 mpg, the compliance people will force a design rule on engineering to use the minimum viscosity.

So the oil viscosity required is a tradeoff between temperature, load, rpm, and film thickness, and of course, CAFE.

 

[widman]

As for psi and rpm, remember that somewhere around 3,000 rpm the relief valve on the oil pump opens to eliminate excess pressure and keep some oil in the pan to circulate.
I like to stick with what the manufacturer recommends until it starts to consume. Then I rains one grade. From an xw30 to a 15w40, or a 15w40 to a 20w50. The little extra viscosity seals better, quiets lifters, and reduces consumption.
But the Salem quote was missing something. CG-4 came out two years before SJ.

 

[satterfi]

I doubt engines are designed for oil weight. I'd think they are designed for power, fuel economy, torque curve, max hp....

quote:

---

Originally posted by TooSlick:
Bob,

I agree with you 100% ...I think running a 15w-40 diesel oil in an engine designed for a 5w-30/10w-30 does not make lots of technical sense. This is paticularly true in cold weather, when you want the oil to flow well during startup/warmup. A fair amount of your engine wear takes place during this period, especially in short trip driving.

What you want to achieve is optimium oil pressure, regardless of the ambient temps. As long as you are seeing 15-25 psi/1000 rpms of engine speed, you aren't going to have issues with bearing wear. At that point the efficiency of your air/oil filters is more important in preventing wear.

If your oil pressure is marginal or oil consumption is high, only then does it make sense to go up an SAE grade in oil selection. Even then I'd probably only do it in warm weather ....

TooSlick

---

 

[jason07-1zzfe]

Molakule, I am somewhat confused on what you said. If the film thickness only increases 1.5micron with each SAE grade, it does not seem that clearances are the determining factor for viscosity selection.
That would also seem to indicate that there is no such thing as too thick an oil, assuming it is able to pump at temp you are using it at. Then I could just as well (and probably with better wear) use a 15w40 on these new engines recommending 5w20!

 

[pgtr]

Cool! Somebody finally mentioned CAFE - thanks Molakule!

In my neck of the woods the local radio-mechanic (who hawks synth) doesn't believe in 5W30 and is real 'border line' on 10W30. I'm in S. Texas (hot) and he feels they are 'designated' by a bunch of cold weather northern engineers that don't appreciate the heat of the SW United States. He also points out that those oils are selected to squeeze very MPG out of the engine and that manufacturers don't care about engine life beyond say 100K. Don't slay the messenger! I'm just repeating.

As to the outside temp thing I'm not sure I fully follow this argument for thicker oils. In a water cooled engine aren't oil temps fairly immune to external temp after warmup? I know there is some effect but I'd guess it to be relatively subtle (less than 5 deg?). Wether it's 80 or 120 outside I figure the oil temp is still going to land right around 200ish or so. Now air cooled would be a different thing altogether of course. Anyway just my opinion...

As to CAFE - yes I see some logic in that argument against lighter oils and 5W sure sounds thin down here in S. Texas.

I saw 15W40 "diesel" mentioned earlier. Actually in a dino I think that sounds pretty darn good. I think it's got a good base weigth to work from and a nice tight spread on the vis. I don't have the owners manual in front of me but I'm pretty sure this is the most dominant oil weight recommended for most temp ranges for our Bimmer. I looked at some bottles of this stuff in the dept store and it specifically said it meets API diesel AND gas. I would have no qualms about using this.

I'm well aware of the historical and valid problems w/ 10W40. In some cases you can even find warranties voided if 10W40 is used. However IMHO this is a fairly dated stigma and is probably overcome in this day and age. Still I tend to avoid it as the stigma has really 'stuck' to this oil.

 

[sprintman]

FYI. Redline Oz tell me 10W40 biggest seller for them here. Better than the usual 20W50 dino I guess?