GREGGPENN

Several of you may have noticed (and tried) the alternative Castrol synthetic lube that ZF6doc.com recommends. I did. The Castrol was in my car during the entire 2004 year. During that time I put about 6K on it and drove it in temperatures ranging from 30-100 degrees.

The first thing I noticed after switching to the Castrol was stiffer (notchier) shifting -- though it smoothed out once the car was good and warm. Bill @ ZFDOC suspected impending hydraulic problems. He said no one EVER reported problems after switching lubes. However, I'm here to qualify that claim.

Last week, I changed back to the factory lube and the notchiness has disappeared. The car now shifts fine -- even below 50 degrees. Please know there is a difference in the weight of the two lubes. The factory lube 5-30W vs. Castrol's 10-60W. So there is a clear reason for the difference!

In my opinion, the Castrol takes about 10 miles (or 10-15 minutes) worth of driving to warm up and perform like the factory lube. Since that is the distance of my average trip, the change to Castol now seems a disadvantage.

Keep in mind that Bill lives in Arizona -- which is typically a warmer climate than many parts of the U.S. Therefore, his experiences/feedback may be skewed from those who've used this lube in warmer climates.

I am certainly not challenging his (or Castrol's) claim that Castrol slows synchro wear, but I must challenge his claim that it will not alter the performance of your transmission -- because it will.

As long as you know that the Castrol will be harder to shift during warm-up -- especially if the outside temp is below 70 degrees, I feel you are better prepared to make the decision on which lube is best for you.

In my case, I've decided the factory 5-30W is more enjoyable to drive. Also, know that the service interval for the Castrol 10-60W is 20K or every year and the price is triple the factory lube (~$30/quart). Also, the factory lube doesn't require changing nearly as often.

So, the Castrol costs more, takes longer to "warm up", and requires changing more often. That doesn't mean it's not the better choice, it only means you need to know the trade-offs.

Gregg

kwik_ta

Interesting analysis... :

HURRICANES99

I have recently spoke will Bill and he recomended bmw M3 synthetic motor oil for the ZF. Would that be the same as the Castrol? Has anyone tried this???? I need to change mine soon.....probably stick with factory oil..

Red Tornado

Although I haven't driven my vette since last November, I live in PA climates and switched to the Castrol 10w-60 (BMW) lube and loved it. 67k miles at the time. No difference in feel vs. the GM fill, at least that I could tell.

wake

Interesting observation, but you did have one error... The Castrol is not $30/qt, it's $7/qt at your (or at least my) local BMW dealership...

GREGGPENN

Same thing.

GREGGPENN

My quote was not an error. But evidently, it was highway robbery -- because that's what I paid last year.

gp

P.S. The Castol 10-60W is the ENGINE oil used in the M3. So don't be surprised when you hear this. Also, you pretty much need to purchase it through a BMW dealership because it's not widely distributed.

bogus

Empirical Data That wonderful thing when supposition has been replaced with fact.

I don't see that here.

I have been using Castrol 10W-60 for nearly 3 years, and that includes Delaware winters. I never found "notchy" shifting behaviour even in sub-freezing weather.

Yes, Castrol is an engine oil - so is the "gear" oil that GM sells, it's just got some friction modifiers that make it better for gearboxes.

The Castrol is not so much the M3 oil, as it is the M5 engine oil. That's where it first game into play. Also note, on the bottle, it meets all Porsche and BMW requirements for "Special Duty".

And not just any engine oil should go into these boxes. I tried some Mobil 1 20-50 oil once (clutch change, and forgot to get new oil), and that stuff stunk. It would not shift to save it's life. I switched back to Castrol 10-60 and all was good.

As for the price you quote, someone raped you, dude. The normal price is about $8.00 a litre (as stated elsewhere in this thread).

You are correct that is not "widely distributed", that's cause BMW is the import for that grade, not Castrol. Technically, the only place you will find it is at your local BMW dealer. It does popup at some online BMW sites, but it is not a Castrol stock item. Call it a captive import.

All in all, I wonder about the condition of your gearbox. If the heavier oil is causing you stiff shifting, then I wonder if the stock syncros are not going south. What kind of mileage does your car have on it?

As stated above, I have driven my 1992 6spd in many different weather conditions, and even as temps dipped into the teens and 20s, the transmission never shifted any stiffer, vs the GM fill. My car has ~134k miles on it.

Perfusion

Mikez40

I am using Red Line MLT in mine. I think I paid about $7.xx/quart.

Perfusion

That's the stuff I use as well... I'll probably just go back to factory fill at my next change.

GREGGPENN

Jeez, what do you want me to do, tear the car apart and perform measurements? Why don't you just call me a liar?

What I can feel is not made up. Additionally, I think you should try switching back to stock lube before concluding my OBSERVATIONS are bunk.

I am more observant/critical than the average person -- and a relatively noticable difference to me may not be terribly perceivable to the next person. However, if you make the change from one lube to the other, you should be able to feel some difference.

There's 48K miles on my car and I cannot detect a difference since last year. If the synchros are "going South", they're taking there damn time about it.

Finally, I never said which lube is better -- only what serves me best. That does not require proof. If the two lubes can be similarly purchased, the Castrol will still be more expensive -- because you must change it more often. If it prolongs the tranny life, then I'm sure that's worth it.

But that doesn't change the fact that stock lube is thinner and I can feel it. But you have to make the comparison/observation immediately before/after a change to really notice it.

I should add that other posters have indicated that their ZF6's can be notchy until warmed up. And some of them use the Castrol. May be synchro related or it may be a perception issue.

gp

ToyC4

interesting stuff!

xlr8nflorida

I'm all for bigger and better but quite frankly the stock lube works fine for me.

All my cars go well over 100,000 miles before i sell them.

I just think sometimes we try to reinvent the wheel - I trust GM.

It's not to say that there aren't other oils that would be better but quite frankly I don't need my transmission to last 350,000 miles.

It's like the debate between Mobil 1, Amsoil and Royal Purple.

The Mobil 1 does a great job, is the recommended fill and will make your engine go several hundred thousand miles.

bogus

My problem wasn't your analysis, it was the limited single case, and the final "this stuff is bad" kinda attitude. I am not calling you a liar, just that the amt of data isn't there.

I have had my 92 for 5 years, and have run both oils... I have found no real difference in the shift quality when cold. In honour of full disclosure, I do have a hurst shifter, so that might just reduce the effects of temperature related notchiness.

48k isn't enough mileage for synro wear. What I am saying, tho, is that each unit is different, and you might have a tight box, whereas mine, with many more miles, is well outside of normal tolerances.

The number one cause of notchy shifting in a ZF is the clutch and or the clutch hydraulics. However, if your hydraulics are a bit off, I would not replace, considering the current state of replacement parts...

Further, I checked www.zfdoc.com, and confirmed my suspicions, the fluid, regardless of what you use, should be changed every 10k~12k miles, due to floating metal in the oil - there is no filter, remember. The quote, as cut from the site: In Conclusion, until someone invents a copper magnet, we recommend that the ZF S6-40 6-speed transmission oil be changed at 10,000 - 12,000 mile intervals so as to minimize the amount of deposits of the suspended spent synchronizer material from collecting in critical component contact surface areas.

I know that GM states that the oil never needs to be changed in the ZF, but they are smoking crack on that one. Some have suggested 30k, others 50k. Personally, I do mine once a year (and it's nearly due).

The reason that oils can last longer in a gearbox (suspended particals not withstanding) is the fact that gasoline isn't present. Gas is the number one killer of motor oil. Gas sneaks into the oil and starts the breakdown. Now, synthetics are much more resistant, but combustion gases eventually break synthetics down... gearboxes and differentials don't have that problem, hense, the long service lives. However, temperature, heat cycling and general wear will cause the oil to eventually loose it's ability to lubricate.

If the transmission had a filter system, then the oil would last 100k miles with zero problems. Might have to replace the filter at 50k mile intervals, but that's about it. www.zfdoc.com sells a kick *** transmission cooler. I have thought a filter might be a nice addition to that setup. It will keep the transmission temps down, and, add volume to the system. Finally, with a filter, I would bet money that the oil would last that aformentioned 100k miles.

Atok

Well I for one agree with your cold temperature theory. I live in Northeast Canada where cold temps are common. I switched the the Castol oil and noticed the same thing you did. It is notchy when cold and smooths out after driving for a few miles. Since I don't drive in real cold weather I decided to leave the Castol oil in.

I don't agree with your statement of the Castol oil needing changing more often. The Castol stuff is synthetic, the GM factory fill is dino oil. BTW, I drained about an ounce out of my transmission last week to do a visual inspection. After 2 years it looks as good as the day I put it in.

White Six Speed

I agree, since I put in the Castrol Oil right after I bought my Corvette, I have noticed the same thing when the tempature was cold out. Next change will not be Castrol

rocco16

It' also my understanding that the tremendous shearing actions that takes place on a gear lubricant breaks the oil down.

I still can't figure out a 10-20K miles change interval for gearbox oil on our ZF's. How many standard Ford/Chevy/Dodge pickup trucks go 300K miles without a single manual gearbox lube change?

(I will go with a 30K mile change interval on mine...)

Larry
code5coupe

VR'92

Well I'm with bogus here again. The Castrol 10w-60 completly changed the feel of my higher milage ZF for the better.

I love the feel now. Much better than the GM fill imo.

Surley there wouldn't a bias against a non GM product on a Corvette site.

dizwiz24

quote:
In my case, I've decided the factory 5-30W is more enjoyable to drive. Also, know that the service interval for the Castrol 10-60W is 20K or every year and the price is triple the factory lube (~$30/quart). Also, the factory lube doesn't require changing nearly as often.

So, the Castrol costs more, takes longer to "warm up", and requires changing more often. That doesn't mean it's not the better choice, it only means you need to know the trade-offs.

Gregg

Amen! Its not just me. I have had much better luck after switching back to the GM stuff as well.

I had grinding on the 1-2 shifts, I got suggestions that I needed a rebuilded ZF6 at a cost of thousands of dollars. All I did was switch back to the GM factory fill and the problems disappeared!

Funny.