Honda Z1 had a viscosity of 29 and 7 at 40c and at 100c respectively. Units are cSt. The new DW-1 has a viscosity of 25 and 6.8, and that goes along with its claim of improving cold weather fuel efficiency. Looking at other ATFs that are suitable for Hondas, Valvoline MaxLife ATF is 28 and 6.1 and Castrol IMV is 36 and 8. Those two are quite a bit different from the OEM fluid. How critical is viscosity to ATF operation, and how would a fluid that is more viscous or less viscous affect operation and/or shift quality?
What function does visc. play in ATF?
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I believe the difference is in fuel efficiency only.
Example: Toyota's WS ATF is low viscosity like 5cst @100 and that replaced mineral (or blend) TIV ATF that was 7cst @100. TIV would share down to 5cst, WS is more shear resistant. The benefit is better fuel efficiency since WS starts lower and stays the same.
Same thing is using shear resistant 5W20 engine oils vs 5W30 oils that shear down to 5W20 at the end of the OCI.
Example: Toyota's WS ATF is low viscosity like 5cst @100 and that replaced mineral (or blend) TIV ATF that was 7cst @100. TIV would share down to 5cst, WS is more shear resistant. The benefit is better fuel efficiency since WS starts lower and stays the same.
Same thing is using shear resistant 5W20 engine oils vs 5W30 oils that shear down to 5W20 at the end of the OCI.
Having used both Z-1 and Maxlife in our Honda, it doesn't matter a whit for our application. Shifting is better on the Maxlife, while fuel economy seems to be unchanged.
As long as viscosity is roughly in the ballpark, other things like additive compatibility and fluid shear resistance are more concerning to me.
As long as viscosity is roughly in the ballpark, other things like additive compatibility and fluid shear resistance are more concerning to me.
Another good example is in normal driving temp of tranny varries, so the actual viscosity varies too. Yet, there are no severe issues with shifting when cold or hot. The only issue I noticed that if tranny overheats (I'm talking big time), the shifts are delayed with slamming into gear. But it would have to be 2 cst or so to produce that (OK, I'm guessing here).
ATF seems to be going to a smaller spread of cold/warm/hot viscosity.
This is good for a couple of reasons.
Cold performance is better, and more precise valving and clearances on new trannys like the thin oil.
This is good for a couple of reasons.
Cold performance is better, and more precise valving and clearances on new trannys like the thin oil.
I mentioned the various fluids for Honda ATs only because I'm familiar with those choices and they do have rather different viscosity numbers. But I guess my question is more theoretical.
Does viscosity play a part in building pressure for shifting and/or valve body operation? For example, if a fluid had too low of a viscosity, could the shifting actually feel "softer" because it can't build the pressure required for the shift? In that sense, especially if in a climate that gets warm, a more viscous fluid might be more optimal.
I have used only Honda fluid in our Acura, and while the shifting is butter-smooth (I really couldn't ask for a better-behaved transmission), some shifts seem to get too soft when the transmission fluid has gotten pretty hot (like after a long drive on a hot day). I think the Honda fluid (at least the older Z1) has a reputation for shearing rather quickly with use. Perhaps the DW-1 does also, I don't know. But it would seem to me that as the fluid gets thinner, the shifting might get smoother or softer, and as the fluid is thicker, the shifting might be firmer.
I also question shift speed. The actual amount of time it takes for the transmission to execute a shift. Is that mainly dependent on the mechanics of the transmission, and shift speed will be what shift speed will be, mostly irrelevant of fluid used? Or does fluid viscosity (or makeup) affect shift speed as well? Presumably, one would want to quicken the shift speed, to spend less time "on the clutches".
A few months ago, I ran 6 quarts of DW-1 through our Honda, and just last week, I ran 3 quarts of Valvoline MaxLife through it. Initially, the transmission was fairly firm on MaxLife, almost "abrupt". But after some more miles, it has seemed to smooth out. This is one of the reasons I asked the question to begin with: the MaxLife starts out fairly thin (only 6.1 cSt), but I do imagine that it is more shear-stable than the Honda fluid. I don't know that for sure, however.
Great discussion; please keep it going!
Does viscosity play a part in building pressure for shifting and/or valve body operation? For example, if a fluid had too low of a viscosity, could the shifting actually feel "softer" because it can't build the pressure required for the shift? In that sense, especially if in a climate that gets warm, a more viscous fluid might be more optimal.
I have used only Honda fluid in our Acura, and while the shifting is butter-smooth (I really couldn't ask for a better-behaved transmission), some shifts seem to get too soft when the transmission fluid has gotten pretty hot (like after a long drive on a hot day). I think the Honda fluid (at least the older Z1) has a reputation for shearing rather quickly with use. Perhaps the DW-1 does also, I don't know. But it would seem to me that as the fluid gets thinner, the shifting might get smoother or softer, and as the fluid is thicker, the shifting might be firmer.
I also question shift speed. The actual amount of time it takes for the transmission to execute a shift. Is that mainly dependent on the mechanics of the transmission, and shift speed will be what shift speed will be, mostly irrelevant of fluid used? Or does fluid viscosity (or makeup) affect shift speed as well? Presumably, one would want to quicken the shift speed, to spend less time "on the clutches".
A few months ago, I ran 6 quarts of DW-1 through our Honda, and just last week, I ran 3 quarts of Valvoline MaxLife through it. Initially, the transmission was fairly firm on MaxLife, almost "abrupt". But after some more miles, it has seemed to smooth out. This is one of the reasons I asked the question to begin with: the MaxLife starts out fairly thin (only 6.1 cSt), but I do imagine that it is more shear-stable than the Honda fluid. I don't know that for sure, however.
Great discussion; please keep it going!
Yes, if the fluid pressure is too low, then you will have shifting problems. It's usually due to leaking seals rather than low viscosity. If you drive high speeds, like 85+MPH, in hot weather, tranny will see excessive temps. I would invest in tranny cooler rather than going into thicker ATF.
I believe a lot of today's transmission will self adjust its shifting to compensate for the fluid visc. That's why after a bit the shifting will smooth out.
MolaKule
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One would like the fluid to have the viscosity of water, which is 0.66 cSt@40C.
But, we need a finite amount of viscosity for the reason given below.
But no lubricant design so far has achieved that viscosity, although ATF lubricants have been developed as low as approx. 4 cSt for newer transmissions.
In tranny design, the pump, channels and piping are designed to pump a certain volume and flow rate at various rpms and temperature swings in order to achieve certain pressures.
Now too high a viscosity can cause cavitaton (especially at low temperatures) and energy loss in certain hydraulic system designs. The energy loss is a result of having to push too high a viscosity fluid around the system, thus reducing efficiency and increasing fluid temperature.
Now, why do we need a low viscosity fluid for hydraulic systems like AT's?
Quote:
We need a finite amount of viscosity for the reason given below.
It turns out the lower the viscosity of a fluid the less tendency to have turbulent flow. Turbulent flow induces foaming and reduces heat transfer. So the lower the viscosity, the less tendency to foam, less power needed to push the fluid around, and better cooling of parts.
I dont think a viscosity variation of 2.5 cSt is going to cause oprational changes, all other things being equal.
But, we need a finite amount of viscosity for the reason given below.
But no lubricant design so far has achieved that viscosity, although ATF lubricants have been developed as low as approx. 4 cSt for newer transmissions.
In tranny design, the pump, channels and piping are designed to pump a certain volume and flow rate at various rpms and temperature swings in order to achieve certain pressures.
Now too high a viscosity can cause cavitaton (especially at low temperatures) and energy loss in certain hydraulic system designs. The energy loss is a result of having to push too high a viscosity fluid around the system, thus reducing efficiency and increasing fluid temperature.
Now, why do we need a low viscosity fluid for hydraulic systems like AT's?
Quote:
We need a finite amount of viscosity for the reason given below.
It turns out the lower the viscosity of a fluid the less tendency to have turbulent flow. Turbulent flow induces foaming and reduces heat transfer. So the lower the viscosity, the less tendency to foam, less power needed to push the fluid around, and better cooling of parts.
I dont think a viscosity variation of 2.5 cSt is going to cause oprational changes, all other things being equal.
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I think water has a 1 c viscosity .
it actually depends on the temp of the water.
but I believe molakule was talking about at 40C
see this link I found on google in 3.5seconds
but I believe molakule was talking about at 40C
see this link I found on google in 3.5seconds
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Thanks guys for all the great responses.
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