Gear, Engine, and MTF Oils

[95metro]

I thought this info was generic enough that it could use its own thread. I've used the recommended manual transmission fluid for Swift Clones as a primary reference, but it still applies to general lubrication:

The transmission/gear oil discussion kind of peaked my curiosity so I've done a little research.

Apparently gear oils and engine oils are actually the same viscosities, but are given different measurements by the SAE to differentiate their uses:

SAE gear and engine numbers cover the same range of viscosities; for example, an SAE 30 engine oil has approximately the same viscosity as a SAE 85W gear oil. This is because the formulation of engine oils is very different to that of gear oils in the automotive industry. An engine oil is far more stressed than a gear oil because it must cope with combustion by-products and blow-by gases which severely degrade the oil. As a result engine oils contain a much wider variety of additives than gear oils. Although not ideal, an engine oil will function in a gearbox while a gear oil will destroy an engine.

Quoted from: http://www.wearcheck.com/literature/techdoc/WZA007.htm (stupid layout on the website, but good info)

A pdf on Redline's website confirmed this by helpfully stating the gear and engine viscosities. 75W90 gear oil is similar to 15W40 motor oil, but the GM/Penzoil Synchromesh is actually closer to 5W30 motor oil viscosity.

Here are some fluid comparisons:

Legend:
Pour Point: Pourability at temperature (°C)
Viscosity Index: The higher the number, the less change in viscosity throughout temperature range
cSt @ 40: Kinematic viscosity in centistokes at 40°C
cSt @ 100: Kinematic viscosity in centistokes at 100°C

Short bit on kinematic viscosity:

In order to determine the differences between the three oils one has to look at the kinematic viscosity of each lubricant. The kinematic viscosity is essentially the amount of time, in centistokes, that it takes for a specified volume of the lubricant to flow through a fixed diameter orifice at a given temperature.

Quoted from: http://www.synthetic-oil-tech.com/d....weight_oil.htm

Penzoil 75w90 GL-4 (basically what the Metro manual calls for, but it's not the correct stuff!)
http://www.pzlqs.com/Tech/Pdsheet/Do...E75W90GL-4.PDF
Pour Point: -42
Viscosity Index: 149
cSt @ 40: 108
cSt @ 100: 15.3

Penzoil Synchromesh (apparently this is the GM synchromesh)
http://www.pzlqs.com/Tech/Pdsheet/Do...omeshFluid.PDF
Pour Point: -50
Viscosity Index: 208
cSt @ 40: 41.6
cSt @ 100: 9.08

Amsoil Synchromesh 5W-30
http://www.amsoil.com/StoreFront/mtf.aspx
Pour Point: -45
Viscosity Index: 194
cSt @ 40: 47.1
cSt @ 100: 9.6

Royal Purple Synchromax
http://www.royalpurple.com/prodsa/scmax.html
Pour Point: -51 (their PDF states -40...???)
Viscosity Index: 196
cSt @ 40: 35.3
cSt @ 100: 7.7

Redline MTL (70W80 gear or 5W30 engine)
http://www.redlineoil.com/pdf/6.pdf (pdf for a number of Redline transmission fluids)
Pour Point: -50
Viscosity Index: 183
cSt @ 40: 56.2
cSt @ 100: 10.6

Mobil 1 5W-30 Synthetic (engine oil - just threw it in to see the difference)
http://www.mobil1.com/USA-English/Lu...bil1_5W-30.asp
Pour Point: -54
Viscosity Index: 169
cSt @ 40: 64.8
cSt @ 100: 11.3

EDIT: The characteristics of some of these MTFs is very close to some 0W30 motor oils. Looks like krousdb's method may be perfect...???

https://www.amsoil.com/storefront/tso.aspx

Mobil 1 0W-20 Synthetic (engine oil - spec sheet is discontinued - they appear to be changing the formulation)
http://www.mobil.com/USA-English/Lub...bil1_0W-20.asp
Pour Point: -57 (newer website info claims -53)
Viscosity Index: 165
cSt @ 40: 43
cSt @ 100: 8.4

[krousdb]

Yup, 0W-20 for me. Got any data on that?

[95metro]

What brand are you using?

[krousdb]

Mobil 1 of course.

[95metro]

Okay, added some Mobil 1 0W-20 info. It looks like they are changing the formula though. The data sheet was not available directly from the product description website.

So, Dan, what made you go with 0W-20 anyway? I just read a website where the guy claimed that 0W-20 isn't viscous enough for anything and he would be freaked out using it in an engine (though he didn't mention transmission I doubt he would even consider that either).

[krousdb]

If 0W-20 is the recommended viscosity for the HCH, it's good enough for my Prius, Del Sol and VX. The Prius is at 70K with 15K interval oil changes. Runs better than the day I got it and has never been serviced other than the routine maint that I do.

As far as 0W-20 in the tranny, if its good enough for an engine, why not a simple set of gears and bearings?

[katman]

I've been asking the techs at AMSOIL about this and they say that the engine oils don't have the shear strength of the gear lubes. It's all in the additive packages.

[Ryland]

gear oil has things like higher sulfer content that act as a high presure lube between the gears, sence they are presseing, and sliding, altho the sulfer wouldn't hold up well to the heat of the engine, it will also eat some forms of bronze, so unless your tranny calls for a gear oil, don't put a gear oil in! some trannys, like Honda's call for motor oil, or honda manual transmition oil, in a few minutes I have some Amsoil manual transmition fuild showing up that is suposed to be compatible with Honda's and work better then motor oil, we'll find out how it works.

[95metro]

Originally Posted by krousdb

If 0W-20 is the recommended viscosity for the HCH, it's good enough for my Prius, Del Sol and VX. The Prius is at 70K with 15K interval oil changes. Runs better than the day I got it and has never been serviced other than the routine maint that I do.

As far as 0W-20 in the tranny, if its good enough for an engine, why not a simple set of gears and bearings?

I'm amazed that it's actually the recommended fluid for hybrids - or at least the HCH! I didn't know that.

I also just looked at the data again and noticed that Royal Purple is apparently less viscous than 0W-20...???

So, now I am debating about giving 0W-20 a shot in the Metro for the upcoming winter. Obviously if I started hearing lifters clicking or synchros crunching then I wouldn't continue use.

As an alternative I'm very certain that 0W-30 would work perfectly since it's still 30 weight oil. I'm mostly concerned about the -20°C/-4°F weather when things get gummy.

[krousdb]

Yup, I was looking at Bob Barlow's HCH during the Prius Matathon weekend and noticed on the oil filler cap (I think that is where I saw it) 0W-20 Oil. They come from the factory with a special break in oil.

[Matt Timion]

Originally Posted by katman

I've been asking the techs at AMSOIL about this and they say that the engine oils don't have the shear strength of the gear lubes. It's all in the additive packages.

WAIT a second... everyone I've ever talked to has used engine oil on their transmission. I even asked the guy at Autozone and their computer told me just to use engine oil. Who is right?

[95metro]

That's interesting - I must have completely missed Katman's post. That is odd, because everything I read yesterday says the opposite. Engine oils need to be stronger than gear oils. You can use engine oil in transmissions, but not gear oils in engines.

The only difference I've seen in the MTF is the supposed additives to lubricate the synchros. Gear oils seem to be too thick for the synchros, but thinner oils should do the job just fine.

[katman]

You have to remember that most of have light weight toy cars (let the flames begin) and motor oil may be fine in the tranny. But just think about it for a minute, why do you need all the additive that an engine needs in your tranny? You don't! In the tranny and differential and transfer case, you need heavy shear load and sliding protection. In an engine, you have have an oil film between most of the parts.

[Ryland]

the main reason for useing motor oil in your tranny is that motor oil is pretty mild when it comes to reacting with yellow metals, I don't think any car manufactur recomends useing motor oil in the tranny in any new cars, it shouldn't hurt them to use it, but MTF that is labled as safe for yellow metals, or recomended for Honda's is most likely what you want, but motor oil will not last as long, they recomend chainging motor oil in your tranny every two years/60,000 miles, gear oil trannys can go much much longer, like on VW's they recomend changing it when it's contaminated, or tranny is worked on.

[Gary Palmer]

How sure are you about this stuff? It seems to me that if they both start from a similar base and then engine oil get's additive's to enhance some of it's protective qualities, that the sheer qualities and those types of factors would be present in the oil, irrespective of the other additives. It makes me wonder if it isn't more marketing issues than real physical issues.

[95metro]

What katman said about "toy" - ahem - cars may be correct in a way. Fluid type may be more dependant on the type or use of vehicle than on anything else.

I know that a lot of manufacturers do recommend engine oil as their MTF. I had an automatic Toyota Corolla and the owner's manual stated that the manual shift version required 5W-30 motor oil. Obviously this was a light-duty vehicle.

High HP cars, trucks, high-torque diesels, and big rigs are most likely going to need fluids that are a little more heavy-duty in order to last longer and to protect parts.

But, that's just my take on things.

[Gary Palmer]

Well here's what I am puzzled or curious about. I am running engine oil in the transmission on my Honda's. However I've always used gear oil in differentials and transmission's, as that was what was recomended. It seemed to me like when I put the engine oil into the Honda, it has a lot less viscosity than any gear lube I've ever used. I figured it is a partial part of the reason the Honda is able to do better on mileage. However, I typically don't change gear lube unless I have to and I've never had a problem with it. Now I'm wondering if I should try to find an equivalent weight gear lube, instead of the engine oil, so I don't have to change it, or if I should just change it and quit whining, or if I don't really need to worry about it, either way.

[95metro]

I should clarify that I started this thread based on my comments in this thread:

http://www.gassavers.org/showthread.php?t=1293

What got the balling rolling in that thread was this:

3...I probably should change my transmission fluid. The owner's manual calls for gear oil, but the viscosity level of gear oil is like 75w-90. This seems really "sticky" and I especially noticed it during the winter. In -20°C/-4°F the shifter felt like it was moving through glue. Is there lower viscosity gear oil I can safely use? What are some options?

MetroMPG pointed out that the Metro's manual is actually wrong and that GM Synchromesh should be used - much much thinner than gear oil going by his tests. He had tried the gear oil in his first Firefly and actually ended up crunching synchros because it was so heavy.

[MetroMPG]

I also drained the FACTORY fresh gear oil from the Blackfly when I got it and compared it to synthetic 75w-90 by timing how long it took to pour a measured amount of each through a filter.

That's how I figured out that what came in the transmission from the factory was definitely NOT 75w-90. What came OEM was much, much thinner and comparible to 5w-30 engine oil, based solely on its pour rate.

The semi-synth GM synchromesh tranny fluid I ended up using had a pour rate close to 5w-30, based on my garage floor science test.

[95metro]

Originally Posted by MetroMPG

The semi-synth GM synchromesh tranny fluid I ended up using had a pour rate close to 5w-30, based on my garage floor science test.

I wonder if you tested it on a cold day if the pour test would come out closer to 0W-30? The viscosity ratings seem to suggest that.

What I still can't figure out is that Royal Purple's viscosity ratings are even lower than 0W-20...

[MetroMPG]

I did it in the evening, around Nov 22 of last year. If I remember right, it was around 0 C ambient, and I compared the fluids cold. That help?

[95metro]

Oh, well, okay then. As usual you're 20 steps ahead of me...

[Ryland]

they really are differnt from what I've seen, cutting oil is closer to gear oil, then it is to motor oil, and you don't want to use motor oil as a cutting oil because it can't take the presure, it just doesn't work well, however, like I said befor, some of the sulfer compounds in gear oil are not compatible with the bronze bushings in a Honda (and other) tranny, and they will attact, and destroy them, really I'm a little confused as to why honda chose those metals that would lead to them needing motor oil in a tranny, if gear oil would last longer, other then it being thiner, and I supose Honda did start out making motorcycles with a gear box connected to the crank case, so they shared oil.

[JanGeo]

In my rabbit I switched to Amsoil gear oil and that made all the difference in the world in cold weather - couldn't get out of first gear when it was cold - shifted like a summer day after. Use what the manufacturer calls for for the type of oil the use a lighter grade or/and synthetic - bearings and load surface area determine the weight of oil needed in the design of the transmission.