Effect of gear oil viscosity on transmission efficiency (Metro owners take note)

[MetroMPG]

This is great info - thanks for posting. I think I'm going to split off (copy) your post into a dedicated thread as well, since this one seems to be addressed to Metro owners.

Dedicated thread is: http://ecomodder.com/forum/showthrea...ands-8047.html

[Southcross]

I can tell you that the manual transmissions in the late 70s/80s and into the early 90s VWs seem to have the same problems with syncro grinds/etc (Transmission model 02O or 020). Book spec calls for 75w90 also, when I drained my gear oil it was a LOT thinner (like your description of 10w30). Many of us in the VW world have either gone the way of Redline MTL (or similar) or several like myself have gone the Syncromesh route. I run Sunoco Syncromesh in my daily, and I have Royal Purple Syncromesh to run in my race cars. We have ALL noted that the infamous syncro grinds on shifting have either disappeared all together or have greatly reduced (likely due to already permanent damage to the syncro) running Syncromesh.

My ONLY qualm about it is DO NOT buy it directly from a GM dealership.... I got raked over the perverbial coals on its cost

[MetroMPG]

The other thing to consider: GM syncromesh is "semi-synthetic" , if I recall. So its viscosity isn't as stable as temperatures change as a full synth. (Meaning greater efficiency hit for those who experience truly cold temperatures part of the year.)

I've got GM Synchromesh (full retail pop! ) in my car now, but am planning to go to a full synth of the same or lighter weight, soon.

Just trying to decide which, and then seeing if my choice is even available in my small city.

[Southcross]

ahhh.... interesting... I thought ALL syncromesh was atleast a semi, if not a full-synthetic. Is there a "traditional oil" syncromesh?

I bought the Royal Purple stuff from my local PepBoys

[Christ]

Someone wanna try ATF+4 in a manual? It has friction modifiers in it, and it's rated for use in ALL Chrysler auto transmissions, regardless of age. This might really help an Eco-modder or two pick up some more mippigs?

[Southcross]

auto tranny fluid?

[Christ]

Yep, many manual transmissions call for ATF. I think most Ford transmissions actually call for it, but you can use engine oil as well.

[AndyH]

Some scattered thoughts...

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.

Andy

'97 VW Passat TDI wagon 391,000 miles

[herbid]

Here's from mya Mazda Astina Service book,
boaut thspec for transaxle oil:
TransAxle Oil picture by herbid - Photobucket

[aerohead]

cold pumpability testing of full synthetics reveals ease of flow found only in lower viscosity standard oils.
Since there are 3-criteria for oil viscosity ratings,not just one,oil makers are forbidden by law to advertise the fact that their oil might flow like 0-wt.