ZF6 fluid
Team Owner
Joined: May 2002
Posts: 24,337
Likes: 25
From: San Diego , CA Double Yellow DirtBags 1985..Z51..6-speed
IMO, ZFdoc's own information shows the Castrol isn't good enough.
Then why they hell is 60 weight used to begin with? Gee, ya think maybe it's too thick?
Based on that, it sounds like the synchros will only last 90K miles with Castrol fluid. Of course this is all meaningless IMO if it's not compared to anything else. All he says about the factory fluid is it causes glazing on the synchros, but is that necessarily a bad thing?
Originally Posted by ZF doc
After 2 hours of operation, approximately 100 miles, oil sample analysis tests indicated that the viscosity rating was reduced from 60 down to a 43 level. No need to worry, this is a normal occurrence for this heavier type of oil. I attribute this to microscopic-level lubricant-strand trimming through operational loading where all of the oil contents has been passed through gear pressure-loading regions at least a few times.
Originally Posted by ZF doc
(paraphrased) At 15,000 miles the synchronizers experienced an average mass loss of approximately 17% based on reserve-wear-range mass equivalency between 0.062"(new) and 0.048"(spent) gap wear/mass measurements. The oil had enough phosphor-bronze particles suspended in it that deposits began building up inside of the synchronizer sliding sleeves. We recommend that the ZF6 transmission oil be changed at 10,000 - 12,000 mi.
Team Owner
Joined: May 2002
Posts: 24,337
Likes: 25
From: San Diego , CA Double Yellow DirtBags 1985..Z51..6-speed
The other question, is Gear Oil and Motor Oil use a different viscosity scale.
10w30 gear oil is THINNER than 10w30 motor oil. (Does GM use the Gear Oil scale on it's factory ZF lube?)
If that's true, the 60 weight oil is WAYYY off. Maybe not a big issue in Bill's environment, as dizwix mentioned. I know it gets pretty cold in Arizona on winter nights, but I bet Bill isn't doing cold starts on his trans then.
10w30 gear oil is THINNER than 10w30 motor oil. (Does GM use the Gear Oil scale on it's factory ZF lube?)
If that's true, the 60 weight oil is WAYYY off. Maybe not a big issue in Bill's environment, as dizwix mentioned. I know it gets pretty cold in Arizona on winter nights, but I bet Bill isn't doing cold starts on his trans then.
Team Owner
Joined: May 2002
Posts: 24,337
Likes: 25
From: San Diego , CA Double Yellow DirtBags 1985..Z51..6-speed
Hmm. I'm guessing the GM lube uses the crankcase scale? But just compare the 60w vs. 30w there.
Code:
| SAE Gear Viscosity Number | | ________________________________________________________ | | |75W |80W |85W| 90 | 140 | | | |____|_____|___|______________|________________________| | | | | SAE Crank Case Viscosity Number | | ____________________________ | | |10| 20 | 30 | 40 | 50 | | | |__|_____|____|_____|______| | ______________________________________________________________ 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32 34 36 38 40 42 viscosity cSt @ 100 degrees C
Team Owner
Joined: Jun 2001
Posts: 26,196
Likes: 0
From: Orlando FL
St. Jude Donor '08-'09
Check the C4 Faq at the top of the page. When I went to get my GM oil, the part number had changed, so the correct number is listed in the FAQ as well.
Get a giant allen wrench (forgot the size, but its HUGE, its in the link in the FAQ though), a $10 hand pump from the auto parts store, and a big mess later and its not that hard, its just really messy.
Get a giant allen wrench (forgot the size, but its HUGE, its in the link in the FAQ though), a $10 hand pump from the auto parts store, and a big mess later and its not that hard, its just really messy.
Le Mans Master
Joined: Apr 2002
Posts: 5,727
Likes: 47
From: Waukesha WI
St. Jude Donor '15
17mm Hex available at AutoZone (among other places).
I use the 10w60 with peachy results. I also never had much of a cold weather problem in Northern WI with it either. It is recommended by ZF Transmissions (the manufacturer) along with the GM fill. They also recommend some kind of ATF but I have never been able to find the exact spec - i was not very motivated tho.
The thicker oil seemed to help reduce some of the "notchiness" in my transmission from the very new GM fill that was in it.
All in all, it depends on what YOUR transmission wants. Each one is going to be a little different because of its unique wear history. Mine is 150k miles old and I believe it was abused by the PO - it likes 10w60 so that is what I give it. Your's might like 5w30 GM...try it and find out.
I use the 10w60 with peachy results. I also never had much of a cold weather problem in Northern WI with it either. It is recommended by ZF Transmissions (the manufacturer) along with the GM fill. They also recommend some kind of ATF but I have never been able to find the exact spec - i was not very motivated tho.
The thicker oil seemed to help reduce some of the "notchiness" in my transmission from the very new GM fill that was in it.
All in all, it depends on what YOUR transmission wants. Each one is going to be a little different because of its unique wear history. Mine is 150k miles old and I believe it was abused by the PO - it likes 10w60 so that is what I give it. Your's might like 5w30 GM...try it and find out.
Safety Car
Joined: Sep 2000
Posts: 3,524
Likes: 4
From: Hinckley Ohio
17mm Hex available at AutoZone (among other places).
I use the 10w60 with peachy results. I also never had much of a cold weather problem in Northern WI with it either. It is recommended by ZF Transmissions (the manufacturer) along with the GM fill. They also recommend some kind of ATF but I have never been able to find the exact spec - i was not very motivated tho.
The thicker oil seemed to help reduce some of the "notchiness" in my transmission from the very new GM fill that was in it.
All in all, it depends on what YOUR transmission wants. Each one is going to be a little different because of its unique wear history. Mine is 150k miles old and I believe it was abused by the PO - it likes 10w60 so that is what I give it. Your's might like 5w30 GM...try it and find out.
I use the 10w60 with peachy results. I also never had much of a cold weather problem in Northern WI with it either. It is recommended by ZF Transmissions (the manufacturer) along with the GM fill. They also recommend some kind of ATF but I have never been able to find the exact spec - i was not very motivated tho.
The thicker oil seemed to help reduce some of the "notchiness" in my transmission from the very new GM fill that was in it.
All in all, it depends on what YOUR transmission wants. Each one is going to be a little different because of its unique wear history. Mine is 150k miles old and I believe it was abused by the PO - it likes 10w60 so that is what I give it. Your's might like 5w30 GM...try it and find out.
Corvette Stories
The Best of Corvette for Corvette Enthusiasts
5 Best & 5 Worst Corvette Daily Drivers
Joe Kucinski
The Headlights of Every Corvette Generation Explained
Joe Kucinski
5 Best & 5 Most Overrated Corvette Track Packages of All Time!
Joe Kucinski
Every 2027 Corvette Engine Explained
Joe Kucinski
Designer Imagines A Corvette That Looks More Like a Corvette Than the Corvette
Verdad Gallardo
10 Ugly Corvettes That We Still Kinda Love
Joe Kucinski
Top 10 Most Expensive Corvettes Ever Sold on Bring A Trailer
Brett Foote
10 Things Every Corvette Owner Needs (2026 Edition)
Michael S. Palmer
8 Most "Only Corvette Owners Understand" Quirks and Problems
Pouria Savadkouei
Race Director
Joined: Dec 2002
Posts: 13,348
Likes: 233
From: SCMR Rat Pack'r Charter Member..Great Bend KS
Remember this:
10W-30 and 10W-60 are both 10-weight oil. So both will have identical cold weather performance.
The difference is that, when heated, the 10W-30 will maintain the same viscosity as a straight 30-weight at temp, while the 10W-60 will maintain the same viscosity as a straight 60-weight at operating temps; both of which will be thinner than cold 10-weight.
One of the major oil companies had a nice explanation of this on their website at one time, but I can't find it now.
Oil Lesson #4: Multigrade oils are oil that has additives that reduce thinning. E.g. 10W-60 is 10-weight oil that has additives that make it behave more like a 60-weight at high temps.
Prove it to yourself: pour out some 10W-60, at room temperature, into a container. It's thin. Real thin. It's 10W thin because it's 10W oil.
As far as the best lube for the ZF6: if in doubt, use the factory fill. You can hardly go wrong.
The Corvette/ZF engineers were not as clueless as we sometimes want to think. 
EDIT: I use the Castrol oil. But, I don't for a moment believe it is in any way superior to the GM lubricant. Just as good, maybe...
Larry
code5coupe
10W-30 and 10W-60 are both 10-weight oil. So both will have identical cold weather performance.
The difference is that, when heated, the 10W-30 will maintain the same viscosity as a straight 30-weight at temp, while the 10W-60 will maintain the same viscosity as a straight 60-weight at operating temps; both of which will be thinner than cold 10-weight.
One of the major oil companies had a nice explanation of this on their website at one time, but I can't find it now.
Oil Lesson #4: Multigrade oils are oil that has additives that reduce thinning. E.g. 10W-60 is 10-weight oil that has additives that make it behave more like a 60-weight at high temps.
Prove it to yourself: pour out some 10W-60, at room temperature, into a container. It's thin. Real thin. It's 10W thin because it's 10W oil.
As far as the best lube for the ZF6: if in doubt, use the factory fill. You can hardly go wrong.
The Corvette/ZF engineers were not as clueless as we sometimes want to think. EDIT: I use the Castrol oil. But, I don't for a moment believe it is in any way superior to the GM lubricant. Just as good, maybe...
Larry
code5coupe
Last edited by rocco16; Mar 12, 2007 at 05:39 PM.
Le Mans Master
Joined: Apr 2002
Posts: 5,727
Likes: 47
From: Waukesha WI
St. Jude Donor '15
Actually, it is true. ZF (the manufacturer - not ZFDoc) does have a class of ATF that is recommended. However, there are only a few that meet the spec. Check out their website for the classes.
I emailed Martin Vogel from ZF a few years ago and he said the recommended fluid is the GM, the BMW, and the "special ATF".
Believe me, don't believe me, I don't care. I have no intention of using any old ATF in my ZF but if I could find one that meets the spec I might.
EDIT: Found the printout from the email. ZF recommends "ATF according to ZF lubricant class 02F (ZF list of lubricants TE-ML 02)". I used to have a copy of that class somewhere but it disappeared. I do remember not seeing any normal store brands on the list.
EDIT2: Martin also said the recommended oil drain interval is 30-40k miles (48-64k km).
I emailed Martin Vogel from ZF a few years ago and he said the recommended fluid is the GM, the BMW, and the "special ATF".
Believe me, don't believe me, I don't care. I have no intention of using any old ATF in my ZF but if I could find one that meets the spec I might.
EDIT: Found the printout from the email. ZF recommends "ATF according to ZF lubricant class 02F (ZF list of lubricants TE-ML 02)". I used to have a copy of that class somewhere but it disappeared. I do remember not seeing any normal store brands on the list.
EDIT2: Martin also said the recommended oil drain interval is 30-40k miles (48-64k km).
Last edited by Dale1990; Mar 12, 2007 at 09:29 PM.
Team Owner
Joined: May 2002
Posts: 24,337
Likes: 25
From: San Diego , CA Double Yellow DirtBags 1985..Z51..6-speed
Actually, the "W" stands for "winter".
There doesn't seem to be an SAE standard temperature for the cold viscosity rating, some say it's based on the pour point of the equivalent SAE oil, others say it's at 0*F, some say neither, either way, the cold rating is below room temperature.So a 10W60 will pour thicker than an SAE-10 oil at room temp. In whatever freezing temp they picked the winter rating at, it will pour the same.
And this assumes they're rating their gear oil on the motor oil scale, which the probably are. Just looking at it, 30-wt gear oil would be really thin!
I know what you're trying to say, but I just had to open up a can of CFI-EFI on your ***.
Team Owner
Joined: May 2002
Posts: 24,337
Likes: 25
From: San Diego , CA Double Yellow DirtBags 1985..Z51..6-speed
That ZF spec doesn't mention the ZF S6-40 anywhere on it. It has some S6-36 truck transmissions listed. A different spec has other S6 series transmissions on it, but no S6-40. And all the 02F lubes are for vans, truck, and crane transmissions with 80K mile change intervals. And if that doesn't convice you, all the ATFs on that page are made and sold in the middle east, africa, etc, by mfg'rs you've never heard of. So I say its
.But, if Martin is right, here's the 02F list on the top of this page:
http://www01apps.zf.com/kst464/ZF_In...2&downLangID=2
Last edited by CentralCoaster; Mar 13, 2007 at 02:26 AM.
Team Owner
Joined: May 2002
Posts: 24,337
Likes: 25
From: San Diego , CA Double Yellow DirtBags 1985..Z51..6-speed
And if you're not confused yet, I ran a query on Castrol's webpage on recommended oil for the BMW M3 that uses the Castrol TWS 10w60.
Here's the result:
No Match
SM,SL,SJ 10W-60 - This Grade is not currently carried by Castrol. We encourage you to visit your local auto parts store or quick lube and request any of these grades. Please continue to check back often as we are constantly updating our product line to help you with all your automotive needs.
Here's the result:
No Match
SM,SL,SJ 10W-60 - This Grade is not currently carried by Castrol. We encourage you to visit your local auto parts store or quick lube and request any of these grades. Please continue to check back often as we are constantly updating our product line to help you with all your automotive needs.
Team Owner
Joined: May 2002
Posts: 24,337
Likes: 25
From: San Diego , CA Double Yellow DirtBags 1985..Z51..6-speed
It gets better.
Castrol Formula RS 10w60, which I believe was recommended to ZFdoc, maybe was never superceded by Castrol TWS 10w60.
Appears that both oils are still produced. According to BMW, TWS supercedes RS, so I guess they're content with the TWS oil. That doesn't mean ZF is. Who knows, maybe it's the same stuff with different labels depending on where it's sold.
From a BMW board:
And some say the TWS is being replaced by Castrol EDGE. Is BMW just changing their mind, or is Castrol changing the name?
Castrol Formula RS 10w60, which I believe was recommended to ZFdoc, maybe was never superceded by Castrol TWS 10w60.
Appears that both oils are still produced. According to BMW, TWS supercedes RS, so I guess they're content with the TWS oil. That doesn't mean ZF is. Who knows, maybe it's the same stuff with different labels depending on where it's sold.
From a BMW board:
I've nagged at Castrol and finally got technical data sheets for Formula
RS 10-60, and TWS Motorsport 10-60
These two products are clearly different (although similar) as shown on
the data sheets.
TWS Motorsport lists BMW M5 approval, (I think it's E39 M5, but that's
not stated)
Highlight spec differences as follows
Formula RS 10-60
Relative density @ 15.6 deg C = 0.852
Viscosity at 40 deg C = 154.4
Viscosity at 100 deg C = 22.57
Viscosity Index = 175
Flash Point (closed) deg C = 206
Pour point deg C = -27
TBN = 10.14
TWS Motorsport 10-60
Relative density @ 20.0 deg C = 0.865
Viscosity at 40 deg C = 163.1
Viscosity at 100 deg C = 24.3
Viscosity Index = 181
Flash Point (closed) deg C = 198
Pour point deg C = -42
TBN = 8.1
The Castrol technical advisor said the oils were mixable and
interchangeable.
I find it baffling.
RS 10-60, and TWS Motorsport 10-60
These two products are clearly different (although similar) as shown on
the data sheets.
TWS Motorsport lists BMW M5 approval, (I think it's E39 M5, but that's
not stated)
Highlight spec differences as follows
Formula RS 10-60
Relative density @ 15.6 deg C = 0.852
Viscosity at 40 deg C = 154.4
Viscosity at 100 deg C = 22.57
Viscosity Index = 175
Flash Point (closed) deg C = 206
Pour point deg C = -27
TBN = 10.14
TWS Motorsport 10-60
Relative density @ 20.0 deg C = 0.865
Viscosity at 40 deg C = 163.1
Viscosity at 100 deg C = 24.3
Viscosity Index = 181
Flash Point (closed) deg C = 198
Pour point deg C = -42
TBN = 8.1
The Castrol technical advisor said the oils were mixable and
interchangeable.
I find it baffling.
And some say the TWS is being replaced by Castrol EDGE. Is BMW just changing their mind, or is Castrol changing the name?
Last edited by CentralCoaster; Mar 13, 2007 at 12:36 AM.
Le Mans Master
Joined: Apr 2002
Posts: 5,727
Likes: 47
From: Waukesha WI
St. Jude Donor '15
That ZF spec doesn't mention the ZF S6-40 anywhere on it. It has some S6-36 truck transmissions listed. A different spec has other S6 series transmissions on it, but no S6-40. And all the 02F lubes are for vans, truck, and crane transmissions with 80K mile change intervals. And if that doesn't convice you, all the ATFs on that page are made and sold in the middle east, africa, etc, by mfg'rs you've never heard of. So I say its .
But, if Martin is right, here's the 02F list on the top of this page:
http://www01apps.zf.com/kst464/ZF_In...2&downLangID=2
.But, if Martin is right, here's the 02F list on the top of this page:
http://www01apps.zf.com/kst464/ZF_In...2&downLangID=2
Like I eluded to above, I have no intention of recommending someone go out and put any old ATF in their expensive transmission. However, if one can find ATF that meets the spec then it should be a consideration. To say that the only recommended fluids are the GM fill and the Castrol is false.
Safety Car
Joined: Sep 2000
Posts: 3,524
Likes: 4
From: Hinckley Ohio
"C4 Corvette ZF S6-40 6-speed transmission uses engine oil for lubrication. I was told by Jeff Henning, Warranty Administrator of ZF Industries North America, that Engineering of ZF Industries in Germany determined that the BMW imported Castrol (RS superceded by TWS) 10W-60 oil was the recommended alternative to the (GM P/N 1052931) factory-fill oil for use in the ZF S6-40 transmission. In effort to verify ZF Industries alternative lubricant recommendation, we ran our own test series on the BMW imported Castrol TWS 10W-60 oil."
I seem to recall RS just doesn't get exported to the US??????
Also the GM fill is 5w30 not 10w30 as some have referred to it as..
Safety Car
Joined: Sep 2000
Posts: 3,524
Likes: 4
From: Hinckley Ohio
However the plot thickens-----Royal Purple recommends their XPR motor oil as a replacement for the GM spec'd fill!!!!! Wonder if they know what they are talking about and if so what is special about their oil?
http://www.royalpurple.com/techa/tranxref.html
http://www.royalpurple.com/prodsa/rpro.html
I am seriously considering the XPR 5W30-------I am currently running the Castrol 10W60, which seems to be fine, but I am just thinking there just might be an extra 5hp or so in the 5w30 vs 10w60??? I am sure fuel economy etc was part of GM's decision to use 5w30 in the first place.