Transmission Fluid

[01 RT SNAKE]

Ok, I'm not trying to beat a dead horse here, just looking for a little advice. I've searched and read post after post about people running all kinds of different transmission fluids in their cars, however, I'm not quite sold on any of them at this point.

I'm currently running Motul Gear 300 and can say without a doubt, my car shifts absolutely wonderful after the car has been driven for a while. Cold shifts are notchy and I'm wondering if a different oil will help with this without sacrificing any protection.

I'm torn between the Motul I'm currently running, the Amsoil product everyone is so gung ** about and the Castrol Syntorq equivalent that can be obtained from Dodge/GM dealerships. Are one of these oils superior to the other? Does a higher flash point or viscosity rating automatically make one better than the other? What should I be looking for when comparing X to Y to Z?

I'm not concerned about warranty issues because my car is long out of warranty. I'm looking for the best protection and easiest//smoothest shift.

Thanks for any advice in advance and I hope no one get's ticked off about another dang "which tranny fluid should I run" thread!

Mike
2001 RT/10

 

[RobZilla]

I use the syntorq and the cold shifts can be a lil quirky as you described. It goes away usually before I even get outta the neighborhood.

 

[Chuck 98 RT/10]

I use the Dodge factory fill. If Tom Brakes & Fluids recommends something else I'll switch.

 

[SHELBYVIPER]

Amsoil here. No warm up issues and no shifter rattle as with the OEM fluids. Shifts like butter even when cold.

 

[plumcrazy]

I use the Dodge factory fill. If Tom Brakes & Fluids recommends something else I'll switch.

ditto, and never a problem with cold shifts.

 

[01 RT SNAKE]

Shifts like butter even when cold.

No butter here. Shifts are notchy and downright have to fight them sometimes. Once the car has been driven for over 15-20 minutes, they're very smooth.

Does this sound normal or do you think there's an underlying problem? I guess I'll know when I switch to one of the other oils that you guys are reporting no cold shifting problems with....

 

[Tom F&L GoR]

Ok, I'm not trying to beat a dead horse here, just looking for a little advice. I've searched and read post after post about people running all kinds of different transmission fluids in their cars, however, I'm not quite sold on any of them at this point.

I'm currently running Motul Gear 300 and can say without a doubt, my car shifts absolutely wonderful after the car has been driven for a while. Cold shifts are notchy and I'm wondering if a different oil will help with this without sacrificing any protection.

I'm torn between the Motul I'm currently running, the Amsoil product everyone is so gung ** about and the Castrol Syntorq equivalent that can be obtained from Dodge/GM dealerships. Are one of these oils superior to the other? Does a higher flash point or viscosity rating automatically make one better than the other? What should I be looking for when comparing X to Y to Z?

I'm not concerned about warranty issues because my car is long out of warranty. I'm looking for the best protection and easiest//smoothest shift.

Thanks for any advice in advance and I hope no one get's ticked off about another dang "which tranny fluid should I run" thread!

Mike
2001 RT/10

1) Only use API GL-4 oils in a transmission. GL-5 oils are for differentials and have much different chemistry. Some oils claim both GL-4 and GL-5, but don't use a GL-5 only oil. Same for MT-4 oils; that is for HD no-synchro transmissions.

2) Higher flash point simply means it takes a higher temperature before a lighted flame ignites the vapors over the fluid. It is a telling measurement for fuels and for contaminated oils, doesn't really tell you anything about performance of oils.

3) High viscosity (thicker oil) is why it's hard to shift when cold (not enough friction on the synchros to bring them to same speed quickly). What you want to look for is high viscosity index. This implies it behaves like a thick oil when hot, but behaves like a thin oil when cold. For an engine oil, your first clue is the spread between the two designations; a 0W40 oil is high viscosity index, a 15W40 is lower viscosity index. They both have the same viscosity at 100C, so they are both "SAE 40". An SAE 40 oil must be between 12.5cSt and 16.3 cSt. Unfortunately the gear oil specifications are much wider, so an SAE 90 gear oil can be from 13.5 cSt to 24 cSt. Consequently the difference between a 70W90 and a 75W90 is more esoteric than useful.

Thicker is not automatically better. The Castrol Syntorq is actually a 75W-85W. Yes, two "W" numbers, again because the system for gear oil viscosity was developed before the use of synthetics was popular. Mopar rebrands this oil and calls it a 75W-85. Go figure.

Transmission oils and gear oils (and power steering fluids) are supposed to be changed periodically but for the most part are fill-for-life. OEMs therefore spend their own testing time and money to look at a few candidates and pick one that works. I don't mean to be anti-competitive or poo-poo any brand, but you can't go wrong by choosing an OEM oil. In this case it would be the Mopar oil, or as we know now, the Syntorq or the GM Synthetic Manual Transmission Fluid. OEMs won't allow a factory fill supplier to be the single source, either. That means Castrol has to allow licenses to other manufacturers to produce and sell the fluid also.

I have not looked up the Motul oil, but maybe you can compare the kinematic viscosity at 100C; that is usually provided. Perhaps they also show the KV at 40C; the difference between the viscosity values gives you an idea of the viscosity index. Perhaps the "ideal" oil is one that meets the engine/differential/transmission requirement when hot (typically the KV at 100C) and has as high an index as you can afford. Sort of like the 0W-40 Mobil engine oil concept, if Tremec and Chrysler determine that SAE 85 or 85W is the thickness they need when hot, then look for a 75W-85 or 70W-85 oil.

No, I don't want to just pick one brand.

 

[01 RT SNAKE]

Here is some information I obtained about the Motul Gear 300. Tom, can you diagnose this and tell me if this is up to par vs the Syntorq??

PERFORMANCES​

STANDARDS: API GL4 and GL5 / MIL-L-2105D
Very high lubricating power which decreases friction and wear.
Very easy gear shifting.
Thermal stability under high temperature.
Unshearable oil film, even under extreme working conditions.
Extreme pressure, Anti-wear, Anti-corrosion, Anti-foam.​

RECOMMENDATIONS​

Oil change: According to manufacturers' requirements and adjust according to your own use.​

PROPERTIES​

100% synthetic lubricant.
Multigrade.
Viscosity grade SAE​

75W-90​

Density at 15°C (59°F) ASTM D1298 0.868
Viscosity at 40°C (104°F) ASTM D445 105 mm​

2/s
Viscosity at 100°C (212°F) ASTM D445 14.2 mm2/s
Viscosity index ASTM D2270 140
Flash point ASTM D92 200°C / 392°F​

Pour point ASTM D97 -39 °C / -38°F

 

[Tom F&L GoR]

Specifications on the Castrol product are hard to find because it seems to have been developed in conjunction with OEMs. And since you can't get it anywhere else, the explanation is that only OEMs can sell in small bottles; this is why distributors that buy in 16+ gallon sizes often rebottle it and sell to the 4WD truck crowd. (Brembo did the same for the 1992-2000 rear brakes - can't buy individual parts inexpensively.)

In searching the internet (so take with grain of salt) I did find that Syntorq LT {=General Motors (Part #12346190) and Chrysler (Part #4637579)} is

11.9 cSt @ 100*C
64.4 @ 40*C
VI 183 achieved without viscosity index improvers.

So it is thinner than the Motul, but meets the SAE 85W minimum of 11.0 cSt. The tell-tale sign of very good base oils is that the viscosity index is a fairly high 183. If it is true that the formulation has no viscosity index improver additive (which shear in use, making the oil seem thinner after time) then it includes a base oil like a polyolefin ester, the next step "up" from polyalpha olefins (PAO). Motul is famous for using esters as well, so I'm a little surprised theirs is not as high for VI.

Assuming that Motul GL-4 additives performance is equal to Castrol GL-4 additives, the Castrol/GM/Mopar oil would shift better when cold (because it is thinner) and still be thick enough when hot (based on being Dodge factory fill oil).

 

[01 RT SNAKE]

Thanks Tom. I always enjoy reading your posts and your knowledge of oils is priceless! Dodge factory fill it is.

Mike