Friction Modifyers

[Joe C.]

I recently filled the diff of my '65 with 2 tubes of "posi additive", and Valvoline 85W-140 gear oil, which is widely available at the any local auto parts store, right next to the 80W-90. The car lays down two really nice, dark, parallel patches if I decide to get a little rough, so the clutches seem to be working AOK. There is less than 500 miles on this gear oil.

I posted a few weeks ago, and have HEARD your comments, some make good sense, but others are not very convincing. Most say the oil is "too heavy", and "use what GM recommends" (GM recommends 80W-90, but they also don't recommend Rotella 15W-40 for the crankcase, either). I have also heard that 1 tube additive should me more than enough, and that 2 tubes might cause some slippage in the clutches, that makes sense.

I have been all over the Castrol/Valvoline/Mobil websites, and spoken to their "customer service" reps. None of this has been very enlightening. An example of some "expert" advice from the Valvoline representative, was when I indicated that "friction modifyers" are included in the formula for their 80W-90 gear oil. I then asked whether, based on this fact, any "posi additive" needed to be added for a limited slip differential, SHE replied "NO". I stated to another "expert", that since nobody recommends the 85W-140 for passenger vehicle use, then what is it used for? Why is it sitting on the shelf right next to the 80W-90? There was dead silence.

Here is what I am going to do:

1. Remove 1/2 of the posilube/gear oil and reserve for later use. This oil would contain the equivalent of one tube of posilube.
2. Replace this with 80W-90 gear oil.
3. Road test car to check for clutch chatter.
4. Remove the 20 year old gear oil from my '85 Corvette.
5. Replace with the reserved oil from the '65.
6. Add (probably about 1 1/2 pints)80W-90 until full.
7. Road test car to check for clutch chatter.

Any useful comments here would be much appreciated.
Thanks in advance.

Joe

[Duke W.]

Re: Friction Modifyers

About all the heavier weight gear oil is going to do is cause greater windage drag, which could cause the oil to run hotter, reduce RWHP, and increase fuel consumption. The later two would be small and not necessarily be measureable without laboratory equipment.

The heavier weight gear oils are typically recommended for medium and heavy duty truck axles, that see lower average RPM, but much higher loads.

80W-90 GL-5 is recommended for most automotive hypoid axles, and the axle is typically one of the longest lived mechanical systems of the car. If it works don't fix it!

I am not aware of any commonly available 80W-90 gear oils that have the limited slip differential additive. The label may say "suitable for limited slip differentials", but that doesn't mean it has the additive, and typically they do not, and yes they are suitable for limited slip diffs IF you install the additive. There is one synthetic axle oil I am aware of that DOES have the friction modifier. In fact they sell two 80W-90 GL-5s, one with the friction modifier and one without and this is clearly spelled out in their spec sheets.

As far as talking to the "customer service reps" on the phone, it's pretty much a waste of time. Most of these folks are young and inexperienced and can't answer detailed questions. Most manufacturers offer specification sheets online, so this is the best place to start, and if the spec sheet doesn't answer your question, try e-mailing them. This won't necessarily guarantee you a correct answer, but I think you have a better shot than talking to someone on the phone. Whosever reads the e-mail can either go find the answer or forward it to someone who, hopefully, knows the answer.

My suggestion is to start with one 4 oz. bottle of the additive and slightly underfill the diff. Test for chatter, and if there is none, fill the axle to capacity with oil. If there is chatter, add another half bottle and retest.

With less additive, the diff. will probably chatter sooner downstream than if you add two bottles, but less additive will likely increase the Positraction breakaway torque and make it more effective. My philosophy is to add the minimum and change the oil about every 30K miles. As the clutches wear the particles contaminate the oil and eventually form a sludge at the bottom of the axle, but changing the oil on a Positraction axle - say every 30K miles or 10-12 years will keep the axle in good working order longer than if the oil is never changed.

Duke

[Duke W.]

Re: Friction Modifyers PS

15W-40 API CI-4 oil did not exist when your car was built, so it was tough for GM to recommend such oils. The recommendation was for what was back then known as "heavy duty" motor oil, which was oil with a high dose of the critical additives we've discussed, and the 15W-40 weight will meet the 1965 recommended viscosity ranges for most current cold start temperatures assuming you don't drive your vintage Corvette is arctic like winter conditions.

Many heavy duty motor oils back then were dual rated for both spark ignition and compression (diesel) ignition engines such as SE/CD. Specs have changed over the years and the requirements of modern catalyst equipped spark ignition engines have digressed from the requirements of diesel engines. As a result, diesel engine oil have higher concentrations of critical additives because some of these additives' combustion byproducts are harmful to catalysts so their concentrations have been REDUCED in modern spark ignition oils. Modern engines warm up faster, have better fuel control, and fewer sliding surfaces, so they don't actually need as rich an additive package as vintage cars, which is why CI-4 oil is the way to go.

GM did not recommend 80W-90 GL-5 gear oil either. GM recommended 80W-90 gear oil meeting MIL-L-2105D. GL-5 did not exist back then, but it is the modern commercial spec to the mil spec, which likely now has a revision suffix above "D".

Same applies to antifreeze, and brake fluid, but we've been through those before.

On any vintage car you have to look and modern fluid specs, then make a rational decision of what modern fluid is best for the vintage car.

Duke

[Joe C.]

Re: Friction Modifyers PS

Duke:

That is exactly my point. Just because GM did not/does not recommend a product is not reason enough, in my mind, not to use it. Only a detailed explanation, as above, will give me (and probably most folks here) enough "food or thought" to reason out a proper solution.
I have, in fact taken your good advice and filled the '65's crankcase with Shell Rotella 15W-40. I will also heed your advice about NOT using the Rotella (or any other CI-4) motor oil in my "modern" C4.
I have 6 cans of Castrol GTX 10W-40 on hand (which was destined for the '65, before the switch to the Rotella). I will use this for the '85, next oil change. The 1985 owners' manual recommends (there's that word again!)10W-30. Now, this engine has always used about a quart of oil every 2500-3000 miles, since new. I think that now is the time to bump up to a slightly more viscous oil. I also think that in an automotive enterprise as conservative as GM, the engineer's astute advice is often overridden by the corporate "bean counters'" skittishness toward the C A F E standards. What do you think (about the 10W-40, and the bean counters, if you are so inclined).

Joe

[G B.]

What does a "multi-weight" oil rating really mean?

I thought the first number was the actual measured viscosity of that oil grade at a standard temperature.

That makes the second number the viscosity at a particular low temperature, or the lubricating properties under some specified load, or....?

[Duke W.]

Re: Friction Modifyers PS

There's been a move lately toward lower viscosities because there is a slight improvment in fuel economy. The EPA derived fuel economy data are rounded to the next whole number, so the OEMs want to get the actual measured value to xx.5 so they can round up. Personally, I would rather have the additional film strengh of the higher viscosity oil, and since I live in a warm climate and my cars rarely even see 40F, so I use 20W-50 in my modern cars.

GM in particular doesn't like 10W-40. This is because this grade of mineral based oil requires more viscosity index (VI) improver, whose combustion byproducts are thought to be harmful to catalysts.

If your coldest anticipated cold start temperature is no lower than 20F, I would recommend switching to a 20W-50, but I don't see any harm in using your existing stock of 10W-40 in the '85.

Duke

[Duke W.]

Re: Friction Modifyers PS Correction

GM's concern with the additional VI improver is due to it's combustion byproducts forming deposits on the intake valves, which can cause problems on modern EFI engines that are set up to run as lean as possible, especially during cold start and warmup prior to going into closed loop operation.

Intake valve deposits from oil that slips down the valve guides and then oxidized can act as a "sponge" and absorb fuel from the injectors, which leans out the mixture further and can cause both driveability and emission test problems. Likewise, deposit build up on the injector tips can cause spray pattern problems which result in similar symptoms.

Duke

[Wayne W.]

Re: What does a "multi-weight" oil rating really m

Multi-weight oils are misunderstood generally by most people. I have had some people ask if the oil gets thicker or something. Actually it is just like all oils and gets thinner with heat, but the rate of thinning is less, which amounts to it operating like a heaver weight oil at high temperature. A good way of thinking about it is to say that a 10W-40 is like a 10W cold and a 40W hot. It is funny to read the recomendations of old cars like my 33 Cadillac. In the owners manual it specifies 20 weight in cold weather and up to 60W in hot. But tells you to thin it with kerosene if you are going to leave it outside or in an unheated garage. Or if you are going to do extended high speed driving to use a heavy duty 50W. Man, you would be changing the oil every day to meet those recomendations, so the companies have come up with a solution. Multi weight oils.

[Duke W.]

Re: What does a "multi-weight" oil rating really m

For each SAE "weight" such as 30 there is a faily wide range of absolute viscosities, and the oil must meet a particular range of at both 32 degrees F and 212 degrees F. The absolute viscosity is usually measured in what are called centistokes or centiposes and the units are length-squared/per unit time

There are also "winter" grades that have a slightly different ranges.

For example, a 20/20W meets both the viscosity range requirements of a 20 and a 20W. There are no winter viscosity range for weights over 20.

A multiviscosity oil meets the range of the lower weight at 32F and the higher weight at 212F, so a 10W-30 meets the viscosity range of a 10W at 32F and a 30 at 212F.

What this all means is that you can use one oil that will flow well enough to aid starting and initial oil flow in winter weather while still maintaining enough viscosity and film strength to provide adequate lubrication in hot summer weather and high engine operating temperatures.

Such multi-weight oils are often called "year round" oils. Way back when before the advent of multi-vis oils, owners would usually use a different weight oil in the summer and winter, especially if they lived in a climate with extreme winter/summer temperature variation, which is much of the country.

There were some problems with the early multi-vis oils. The VI improvers broke down faily rapidly, so a 10W-30 often became a 10W-15 or 20 before the normal oil change interval.

VI improvers have improved greatly over the years, but they still break down, which is one reason mineral oils should not be run as long, mileagewise, as synthetics. Most 10W-30 synthetics require no viscosity improver, but the broader ranges like 0W-30 and 0W-40 probably do depending on the blend of synthetic base stocks.

Duke

[Joe C.]

Re: Friction Modifyers

Duke:

I am decided on mixing the 80W-90 with the 85W-140 at about a 1:1 ratio as per my above post, because I don't want to waste what is essentially brand new lubricant. The question is, is it alright to mix these different viscosities? My gut tells me that it's just fine, and that the resulting mixture (suspension?) will blend the properties of each grade into a happy compromise. The engineer says go ahead and try it, but the polymer scientist wants to look on a molecular level. The molecular shear stresses will certainly be higher with the higher vis lubes, no question. If you have any information to the contrary, then please let me know.
Now, a few comments:

1. Windage drag on a diff is a function of ring gear angular velocity. Because truck tires have much larger circumferences than car tires, then the truck's ring gear is rotating as a slower rate than that of a car, for any given gear ratio.
2. Last month, I found the Valvoline manuf spec sheet for their petroleum based gear oils, specifically 80W-90, which stated that "friction modifyers" are included. I can no longer find the sheets for their petro based gear oils. I can now only find the product sheets for their synthetic gear oils, specifically 75W-90 which CLEARLY states that friction modifyers are included, and additional is NOT NEEDED.
3.Here is the text of my correspondence with a Valvoline "expert" last month:

---------------------------------------------------------------------------
Thank you for your question! Valvoline recommends that you use 80W-90 gear
oil in both the 1965 and the 1985 Corvette. The 80W-90 gear oil does
contain the limited slip additive.

To: VWEBMAIL@Ashland
cc:

Subject: Site feedback from Valvoline.com

The following person submitted a question or comment via the Contact us
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First Name: Joe
Last Name: Ciaravino
Address1:
Address2:
City: Ocean
State: NJ
Zip Code: 07712
Phone:

Email Address: speedo1952@optonline.net

Comments:

I own two vintage Corvettes: a 1965, and a 1985. I live in New Jersey, and
never drive either car in the winter. All of my driving is in summertime,
and I sometimes subject these cars to severe duty (spirited
driving/occasional drag racing).

I am looking for maximum protection, and fuel economy is only a very minor
consideration.
I need help in picking the right gear oil for my application: either
80W-90, or 85W-140.
How different are the characteristics of these two lubricants, and what are
the advantages/disadvantages or each. Remember that these cars are never
driven when the ambient temps are below approx 50 degrees Fahrenheit. Which
offers better protection? Does either contain a friction modifyer (both
cars have positraction)? Can these two grades be mixed?
Thank you.

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Joe

[Terry F.]

Re: What does a "multi-weight" oil rating really m

First number is flowability at start up (it is the most important number). A
0-W40 would have no resistance to flow at start up. Probably act like water when pouring it out of a container (I think they actually make such oil).The second number defines its viscosity at operation temperture. But how much flowability does and engine need???

First number is most important generally speaking because the sooner you coat the surfaces inside the engine the better. At start up, acids are formed that attack the combustion surfaces, etc. and then build up in the oil. I suspect the wear packages that are put in oil are designed to buffer the acid over time and keep very small particles suspended and not deposited inside the engine.

I believe Duke recommends using high quality diesel motor oil particially because of the added wear package (can't speak for Duke though and I totally respect his opinion). Diesel fuel contains more sulfer, not as refined compared automobile gasoline. Diesel fuel actually contains a lot of different molecules that result in the generation of different types of acids like sulfuric and hydrocloric acid. Just remember that when you start your engine it turns into an acid factory. Even cheap motor oils have more sulfer in them than higher quality motor oils or synthetics. So, diesel engines need more of the wear package stuff to protect them because of the comparatively poor quality of their fuel compared to a standard gas engine.

Todays engineers have to consider how effecient an engine will run and what type of wear protection is needed to protect the engine. In a warm climate how much flowability does an engine oil need? How much flowability difference exists between two different multigrades on a warm day start up? They probably would have to be extremely different to make a difference.

It is known that the wider the viscosity range in general the oil characteristics start to change/break down. After a 1000 miles if you could clean all the crud out of it it still wouldn't be the same oil. Synthetics have an advantage in that they are more stable in that regard. Synthetics also have greater uniformity of molecular size and shape which gives them superior film strength and a stronger hydrodynamic wedge, don't ask me to explain that one. I also believe the synthetics have less of the other acid forming molecules. It cost momey to make a clean uniform motor oil that has a great wear package. I like the idea of the high quality diesel motor oil in these older engines and I think it works.

In an engine that gets only a few drives a year, I would say you should change the oil at least once a year.

I am not an expert, just my opinion that is willing to change with discussion. Regards to everyone, Terry

[Rob A.]

Re: What does a "multi-weight" oil rating really m

Found out recently that the "W" stands for winter, not "weight" as most people think.

[Duke W.]

Re: Friction Modifyers

I wouldn't think that mixing the two different viscosity range gear oils would cause any problems due to some fundamental incompatibility, just like mixing two different viscosity motor oils is very unlikely to cause any problems.

Duke

[Joe C.]

Re: What does a "multi-weight" oil rating really m

Terry:

The most destructive demon for certain automotive working fluids is entrained moisture.
With brake fluid, for example, moisture will be absorbed and suspended in the medium and will significantly degrade the braking performance over time. This is a SAFETY ISSUE, so please err on the side of safety here.
As far as crankcase lubes are concerned, then CONDENSATION is the culprit. Whenever you shut down your engine, the sulfides produced during combustion are combined with the condensate, to form sulfuric acid (H2SO4), which will attack the internal surfaces of your engine. And so it is better to change oil as frequently as possible, especially with a car that is driven very rarely.

[Terry F.]

Re: What does a "multi-weight" oil rating really m

So, how many times a year should you change the oil on a car that gets 2000 miles a summer on it?

Yes I agree the crank case is a chemical factory and water does play into the production of the acids. I would suspect that the water that is not used in the production of acids with each engine cycle would just vapor off with heat.

Thanks, Terry