Detailed discussion of gear oil choices...

[takza]

Concerning issues of syncro mesh...mpg...reliability and wear....


http://ecomodder.com/forum/showthread.p ... s-128.html


I pulled this together for a VW TDI forum. Last update was Oct '07. Most data comes from manufacturer spec sheets, but has been validated and/or expanded with oil analysis. Sorry...it's heavily weighted to Euro and VW fluids.

There's been a steady shift from 80-90 gear lubes to fluids that are basically automatic transmission fluid with some extreme pressure additives in order to improve corporate average fuel economy...so manufacturers can sell more trucks... You can see that the lightest fluids are off the chart...

When it comes to improving fuel economy thru changing fluids, the differential is the largest factor, with tranny second and engine last.

Changing from petroleum to synthetic - even with the same viscosity - can make a significant difference. For example - a class 8 truck (semi) tractor with dual drive axles, when moving from petroleum fluids to real synthetics, can gain 8.3%. 5.25% is the differentials, about .5% is the engine.

I did some highway testing with my old VW diesel - moving from the factory 75W-90 synthetic, to a synthetic synchromesh fluid, down to VW G52, and back up. The move from 75W-90 to the really thin G52 was worth 1.8mpg. In the end I moved back to 75W-90 to keep my 390,000 mile transmission a bit happier.

VI is viscosity index and speaks to viscosity stability as temperatures change. Higher is more resistant to change with temperature.

Transmission fluid viscosity is normally rated at 40C, while engine oils are rated at 100C. And, as already pointed out, the viscosity scales for gear oil and engine oils are different.

Viscosities are in cSt - centistokes - and are essentially a timed flow thru a cup with a hole in it.

(Manual Tranny Fluids)

VI Vis@40C Vis@100C
128 159.0 18.3 = AMSOIL CTL SAE 50 Powershift GL-1
..............16.7 = Motul MOTYLGEAR 75-90 GL-4/-5
..............15.6 = VW G50/G51 GL-4
185 90.0 15.6 = Redline MT-90 75-90 GL-4
..............15.2 = Mobil 1 Synthetic 75W-90 GL-5
..............15.2 = Motul Gear 300 75-90 GL-4/-5
..............15.0 = Elf Tranself Synthese FE 75-90 GL-4/-5
132 116.0 14.9 = AMSOIL AGL 80W-90 GL-5
177 84.5 14.7 = AMSOIL MTG 75-90 GL-4
..... 76.6 14.2 = VW G052-911
133 76.2 11.0 = AMSOIL CTJ SAE 30 Powershift GL-1
183 56.2 10.6 = Redline MTL 70-80 GL-4
194 47.1 9.6 = AMSOIL MTF Synchromesh Trans fluid (GM/Chrysler) GL-?
208 41.6 9.1 = Penzoil Synchromesh trans fluid GL-?
198 34.0 7.5 = Redline D4 ATF Dexron III / Mercon / API GL-4
138 40.5 7.1 = AMSOIL CTG SAE 10W Powershift GL-1
..... 31.2 6.5 = VW G-052-171-A2 GL-?
..... 35.1 6.4 = VW G-055-726-A2 GL-?
..............6.3 = VW G52 (part numbers G052726A2 / G05272601) GL-?

(Automatic Tranny Fluids - except for Redline D4 dual-use)

VI Vis@40C Vis@100C
.............8.3 = Honda CVT Fluid
.............7.6 = Mobil 1 Synthetic ATF

198 33.5 7.5 = Redline D4 ATF Dexron III / Mercon / API GL-4
.............7.4 = Mobil 1 Synthetic Dexron/Mercon
197 32.5 7.2 = Redline Synthetic ATF Dexron II / Mercon
.............7.1 = Mobil 1 Synthetic Multi-vehicle ATF
138 40.5 7.1 = AMSOIL Ford type F auto trans fluid
168 37.4 6.8 = AMSOIL Automatic Transmission Fluid ATF
..........5.5-6 = Ford Mercon SP


There are three basic categories of base oil on the streets. Group I and II are refined petroleum. Group III is refined petroleum that has also been dewaxed (improves low-temp performance) and high-pressure hydrogen processed to improve high temperature performance. Group III can be called 'synthetic' (legal definition) in the Americas but no where else in the world. Group IV is man-made synthetic base oil - PAO. Group V is an 'all others' group and contains petroleum and synthetic products - from Vaseline petroleum jelly to the man-made esters used as a component in lubricating oils.

Most of the products on the North American market - the 'synthetics' and 'synthetic blends' are made with Group III base stock. All of AMSOIL's products (with the exception of the XL products) is Group IV/PAO based. RedLine products are primarily ester based. (Both companies use a combination of PAO and ester.). Mobil 1 products are primarily PAO-based, but some also contain some amount of Group III (legally synthetic, but technically a synthetic blend because of the petroleum-derived content.)

Gear teeth are kept apart by a combination of fluid viscosity and the extreme pressure components in the oil's formula. Moving to a lower viscosity product can increase efficiency but can also result in increased wear rates.

As viscosity thins, the anti-wear additives must be improved to maintain the same low wear rates. Keeping wear in check is important because it's a geometric progression - one piece of steel or grain of sand in a gear box can scrape a pair of pieces from two gear teeth. The three pieces can generate 6 new pieces, the current 9 pieces can generate 18...and away we go.

It's best to match both the viscosity and the performance rating (such as GL-4) when selecting a replacement fluid.

If the transmission is filled with 75W-90 GL-4 petroleum, move to 75W-90 synthetic (AMSOIL, Redline, Mobil 1, or a European product) that also has the GL-4 (or similar OEM rating). Next move might be to something in the Synchromesh arena.

Driver technique and aerodynamics are better first targets - efficiency gains from lighter lubes are measurable but small, and if taken too far can lead to unhappy synchronizers and/or increased wear.

GL-5 is for differentials; GL-4 is for transmissions with 'yellow metals' and synchronizers. The higher levels of extreme pressure additives in GL-5 fluids can destroy brass, bronz, and copper in a manual transmission. Some 'real' synthetics can have dual rated GL-4/GL-5 products because the company found that the heat-activated GL-5 additives don't activate in a cooler running transmission. But it's best to stick with GL-4 or appropriate OEM rating for a synchronized transmission.

Please do not add anything to any finished lubricating oil - including transmission, engine, or differential. At best you're only out a bit of money. At worst one can lose their component warranty, oil warranty, have bearing wear and/or increased rust/corrosion. Lubricating oils are designed and tested specifically for the intended application - don't upset the sensitive chemical balance.

[Snax]

Interesting info. I have frequently wondered whether a change to a lighter batch of lube would improve economy enough to be worth the risk of additional wear.

If I simply coast out of my driveway in gear with the clutch, the front of my car will barely leave the end of it, but if I bump it totally out of gear, I get an extra 5-6 feet of roll past the end. Our Mazda5 by contrast will roll half way down the block either way!

My car has just over 200k miles on it, but I'd love to push it past 300k, so I don't want to go crazy with it. I have no idea what's actually in my gearboxes, but at the very least I suspect a switch to a PAO synthetic might be worth the risk even at the heaviest consumer grade.

Any further thoughts on this?

[takza]

What I find interesting is that at one time I drove a 280ZX (Nissan) 6cyl MP EFI hich typically gets 24 mpg all around. After using a combo of teflon...militec...moly additives in the engine...trans...diff...I saw an definite 8-10% mpg gain...and while using regular weight dino gear oil.

Problem being that I lost my record for that car...so I don't know exactly what I used....generally just one additive in the trans and diff...and used various in the engine every 3K miles.

So what would be the mpg gain if a lighter weight SYNTH oil such as .....198 34.0 7.5 = Redline D4 ATF Dexron III / Mercon / API GL-4....was used in the trans and diff...along with the right additive such as Militec...Tufoil...etc???? And maybe Tufoil and a lighter weight oil in the engine?

With ANY 4x4...the extra drag of 2 working axles means they always get less mpg than a 2WD clone?

In theory...the additive would make up for the lack of viscosity. Maybe a 15% mpg gain?

[animeracing]

The increased wear caused by using a lower viscosity lubricant ISN'T worth it.

The general thinking was that with the technological advances in lubricants, you could get the same wear protection with a lower viscosity synthetic as you would back in the 80's with the traditional petroleum based stuff. This seems to make sense when you see that engines now run with 0W-20 motor oil and the latest tramsmissions/transaxles are using synthetic fluids that are low viscosity as well.

However, a good bit of the discussions I've read seem to result in a bad ending. Someone swaps gear oil for ATF in their older car, and the gears wear super fast and something breaks or seizes, transmissions overheat or start slipping, etc.

My suggestion would be to stick with the same fluid type and viscosity, but just get the synthetic you prefer. I've changed everything over to Castrol Syntec synthetics (not that this is a promo, Mobil 1 has good stuff too), and haven't had a problem. The difference is noticeable, synthetic ATF in the tranny had it shifting super smooth and positive, synthetic 75W-90 gear oil seemed to make for a smoother cruise, and MPG overall went up slightly with no additional mods at the same time.

Synthetics? Worth it. Especially in transmission/differential/transfer case applications with their higher mileage (than engine oil, at least) fluid change intervals.

Experimenting with viscosites for the drivetrain? Not worth it at all, especially on hard working drivetrains like the T4WD, or any rugged vehicle, light or heavy duty.

I suppose you could use 5W-30 oil in the motor in a cold climate though.

[Snax]

I tend to agree with that line of thinking. The primary difference I think as to why one would be ok to lighten the engine oil vs. the driveline comes down to the type of surfaces being lubricated, i.e., bearings vs. gear faces.

With respect to the dino vs. synthetic decision, I think synths are the clear winner regardless of where they are used. Their viscosity tends to be more consistant throughout the temperature range and they are not subject to breakdown as easily from heat and contamination.

[takza]

Well...I'm talking in generalities as much as anything. With a car below 100K miles...I'd probably try the thin stuff...with the right additives.

Specifically for the T4WD...with the high mileage on the transaxles....might be an issue going with lesser viscosity in those...but synth in the OEM weight might help.

The rear diff......seeing little real use in normal driving might use some lighter stuff with the right additive.

The car I saw the 8-10% gain from was 2WD....streamlined...low air resistance....EFI....the kind of vehicle that is more sensitive to things that might improve mpg.

While the T4WD is carbed...has a fairly low CD...but the extra drag from the rear diff/driveshaft keeps it from seeing the better mpg that the 2WD Tercel with 3AC can get. Part of that drag is simply the extra mass of metal that has to be sped up everytime you accelerate...can't do much about that...except maybe use lighter wheels/tires? Only part of it is the drag of the gear oil.

viewtopic.php?f=2&t=4797&p=35596&hilit=+gear+oil#p35596

"So just before we took the Tercel on the 2,500 mile trek, I changed the tranaxel and rear differential over from 89-90 gear lube to Mobile 1 synthetic. First drained the units, cleaned the magnetic plug ends and flushed/cleaned with cheap ATF then drained and filled with the synthetic.
Now I had no way of comparing the improvements to mileage or much of anything for that matter until I did my coasting route down Academy Boulevard. Normally the stop light catches me a Wyoming so when I get green I accelerate to 35 mph and put him in neutral. I have a mile of downhill that only has 1 stop light that I usually cruise through. Now with the 80-90 gear lube, the Tercel would slowly gain speed and top out about 42-45 mph, just the speed limit. This would be the case in summer and in winter with the gear lube viscosity restriction, he would get to 38-39 on this stretch coasting.
Lo and behold, Now he zips right past 45 mph and I actually have to feather the brakes to stay under the speed limit. I know this is not very scientific. I don't care."

[Snax]

Too bad there is no way to easily disengage the rear differential completely. I have no doubt that it accounts for 5-10% of the fuel economy hit vs. the FWD.

The upside, if one does try a lighter weight lube that results in failure, is that the rear differential is relatively easy to replace vs. a transaxle. And given the failure rates of the transaxles vs. the rear differentials, probably more readily available.

[takza]

I changed over to Mobil 1 synth 75w90 LS in transaxle/diff (4x4) along with 1 oz per qt Tufoil.

Went with Mobil 1...0W30 synth oil in the engine (+ 1 oz Tufoil / qt) along with a Pure One PL30001 "Mustang" oil filter on the 1.5L engine. This oil can be found at Walmart for $23/5 qts.

The idea with this large filter (2xs the filter area?) is that it should act something like a bypass filter without the extra expense...and it isn't likely to clog over 12 K miles.

http://forums.noria.com/eve/forums/a/tp ... /937101141

" I've searched the forums and it seems that people choose the Amsoil filter over PureONE on 'faith' that the Amsoil brand is somehow better than every other brand.

After checking the specs for the Amsoil EAO filter and the Purolator PureONE filter I found something shocking... PureONE is actually better by the numbers.

According this this website: http://www.amsoil.com/storefront/eao.aspx

"Amsoil tested their EAO with the industry standard ISO 4548-12 and found that the 15 micron efficiency to be 98.7%

PureONE's ISO 4548-12 for 5 micron is 50%, 10 micron is 92.8%, 15 micron is 99.2%, and 20 micron is 99.9%. [info source: e-mail response from the tech/engineer department].

I've e-mailed Amsoil about the 5/10/20 micron ratings that isn't listed on the website but it would seem that PureONE is better than Amsoil by the 15 micron comparison.

So... PureONE's filter is not recommended for 25,000 miles oil change but Amsoil's EAO is by what logic? I guess if you trap more particles you have to change out the filter more often which means that the Amsoil one is probably letting more things through so it doesn't clog up and go into by-pass valve mode."


Can see why I never did this before...since the almost 6 quarts of gear oil needed can be had for around $20 in dino...and around $60 in synth...and this isn't Redline or Amsoil. But it's good for 30K...so an extra $13 a yr.

Engine oil will run for 1 yr or 12K miles with a filter change at 6 months...expect to add at least 3 qts over one year....including with the filter change.

Engine oil cost should be around the same as regular oil at $3 / qt. Would still have used the Tufoil.

The gear oil was an extra $40 or so...and over 3 yrs it's an extra $13 / yr or so...meaning I'll need to see at least a 2% gain in mpg to pay for it.

Mobil sells a synth Delo gear oil in the same weight but without the LS additive. Usually the parts stores only carry the 140W Delo stuff and usually not in synth...so I went with what they had. The LS is recommended for any GL5 app...and is supposed to reduce the gear shifting problems some mention with synth gear oil. The extra Tufoil will push it more towards a non-LS type gear oil anyway.

Results depend on whether I see extra oil use due to the synth oils and Tufoil...usually haven't when I've used synth oils...sometimes do with additives though.

[takza]

Really liking the way the trans shifts now....real slick...so to speak. None of the occasional mild grinding I saw before with Coastal 80W90 dino oil with moly additive...where I had to concentrate on making sure I used the clutch fully.

I did add 1 oz Tufoil to each quart of Mobil 1 LS 75W90 synth gear oil. Used only 5 qts since the additive added a few oz.

Haven't driven it in colder weather...but I expect it to be better then too.

[takza]

Engine has gone from using a qt every 5 K to around 1 qt per 3 K with the 0w30 synth oil. Have now replaced the distributor o-ring...which should reduce oil loss some. Gear oil seems to be staying IN...not too much in the way of leaks seen.

[Snax]

Some day (soon, hopefully), I will reassemble and install my motor to later report no oil consumption (again, hopefully).

Anyway, a complete gear oil changeover will go with it since I have absolutely no idea what is in there now.

[dlb]

i'm considering swapping to synthetic gear oils in our primary rides since both need to be replaced anyway. i've read conflicting reviews of the stuff on this forum--some suggest trans seals might leak, syncros might wear quickly, etc--but this thread makes me feel more confident that switching to synthetic but sticking with the correct viscosity should be fine. the cost of the synthetic is quite a bit more than the dinosaur stuff but i figure if i have to replace gear oil due to age anyway, i may as well spend a few extra bucks and save on gas in the long run since i likely won't replace the gear oil again for many years.

this is the thread that initially got me thinking about it

https://tercel4wd.com/forums/viewtopic.php?f=2&t=7418

but this thread i'm replying to is more informative.

any further thoughts on the topic?

[dlb]

question: when switching from regular gear oil to synthetic, is it necessary to flush the trans/diff/transfer case with something before putting the synthetic stuff in? my dad seemed to think so but i haven't heard anything about that.