Transmissions picky about fluid.

[Scott]

So I am curious if anyone more knowledgeable than myself can help to explain why some transmissions are so finicky about the type of transmission fluid used. For instance, I own a 2007 Camry and a 2012 Civic. I’ve read numerous accounts of people using Valvoline MaxLife (a full synthetic ATF) in Camry transmissions with great results as opposed to the recommended Toyota ATF WS. In fact, I intend to flush my system soon and replace the factory WS the car is still running on at 64k miles (bought it used at 60k) with the MaxLife. However, I have also read countless recommendations that in Hondas, only the Honda ATF DW-1 be used (Eric being one of them). As such, I have only been using that ATF in the Honda transmission.

So my question is why is the Camry transmission so accommodating to another ATF and the Honda transmission so picky (just using those two examples… I’m more interested in transmissions in general)? I understand that different ATF contain different/specialized additives, etc., but how different can each transmission be that one would die using one ATF while another would run fine? I admittedly only have a basic understanding of how automatic transmissions work via YouTube and some light reading 🙂

Topic

[Mike]

The main thing is that different transmissions have different types of wet clutch materials that are designed to be used with a given additive package so the amount of friction in them is correct. A less common reason is the fluid viscosity. As fluid is used to apply clutches smoothly, the wrong viscosity of oil will change the amount of time it takes to fully apply a clutch (all other things being equal). A newer thing is CVT fluid being specialized for 2 main reasons. First is that it’s a metal belt riding on metal pulleys that cannot be allowed to slip, so the fluid has additives that address that metal to metal contact. Second is that the operating pressure is up to 1000psi as opposed to less than 300psi in conventional autos. The fluid molecules are sheared (breaks down) far more violently and quickly at that pressure, so it has to be very tough.

[Jonathan Stiver]

I use MaxLife ATF in just about everything, even Hondas. It crisps up the shifts in Hondas, which the OEM fluid tries to get away from to make shifting feel more like a conventional automatic. Other than that, everything I’ve put MaxLife in has improved feel and performance.

[zero]

I guess the best way to put it is, would you rather have a one formula fits all in your transmission, or a product specifically designed for it. Not that I’m bashing Valvoline’s products or anything, because I have put whatever variation of Max-Life in many, many cars professionally. But an all-makes repair shop doesn’t want to stock 20 different ATFs because of the cost and the space etc. so a one-size fits all product is the way to go. Since most imports are drain and fill and only use a few liters, trust me a 2012 civic is a hair over 2.5L, I don’t see a reason not to get the exact product required.

[Lorrin Barth]

I own an AWD car and the transfer case requires a special oil. Use just any off the shelf gear oil and the gear box will fail. So, is this an example of the special requirements of modern equipment or is the maker solving a design problem the cheap way by using special oil? This is just my opinion but I suggest the latter is true.

A couple more examples of this would be Subaru with leaky head gaskets requiring special antifreeze and Honda automatic transmissions requiring special oil.

Some years ago Chevrolet testing the then new Corvette found that the engine would starve of oil in hard turns and spin bearings. Various pan designs were tried without success but then somebody suggested trying synthetic oil – it solved the problem. So, the Corvette became one of the first cars to specify synthetic oil.

[Mike]

I think another thing to consider is that the formulation of specific recommended fluids might be matched to the characteristics of the transmission seals and gaskets used by a particular manufacturer.

I’ve known aircraft mechanics who put a certain synthetic hydraulic fluid meant for a particular aircraft in their auto transmissions. (Because they could get it for “free”.) They wound up destroying every seal and gasket in their trannies.

[Author]

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