Heavier Than Recommended Viscosity Transmission Oil - Is it Ever Justified?
On a recent msprotege Forum thread, the question was raised as to whether SOME transmission failures in highly modified engines (especially those that see frequent drag, track or rally racing) might be due to inadequate lubrication rather than to a strength of materials issue. This being a possibility, the suggestion was made that a switch to a heavier viscosity oil might be beneficial in terms of increasing transmission life and reliability. This might be something that those of you with turbo or otherwise heavily modded n.a. engines might want to consider. The question then becomes, what would be an appropriate oil?
All of the following information comes from the Red Line oil website because the company has the most informative, comprehensive and complete array of technical specifications, data and descriptive information of any oil company website I know of.
Red Line makes three classes of oils suitable for M/T cars: Synthetic M/T Lubricant, Synthetic Gear Oil and ShockProof Gear Oil. The synthetic M/T lubricant, MT-90, is considered the oil of choice for our Protege transmissions.
The ShockProof oils (SuperLight, Lightweight and Heavy ShockProof) are not recommended for synchro type transmissions as Red Line considers these oils too slippery for optimal synchro engagement. Consequently, although LightWeight is a 75W-140 rated oil and Heavy is rated at 75W-250, neither oil is suitable as a higher viscosity replacement because of the synchro problem.
In the Gear Oil category, both the 75W-90 and 80W-140 are also not recommended by Red Line for the same reason-both oils are too slippery and thus prevent rapid synchronization. The two Gear Oils Red Line DOES recommend for M/Ts with synchros are 75W-90NS and 75W-140NS (both GL-5 rated oils) because, according to Red Line, "these gear oils don't contain the friction modifiers for limited-slip hypoid differentials. This makes the transmission synchronizers come to equal speeds more quickly, allowing faster shifting and much easier low-temperature shifting." Further proof of the suitability of these oils for our transmissions rests on the fact that these two oils are also listed in the M/T lubricant category along with MTL and MT-90. Clearly, it would seem that for those who think they may need a heavier viscosity M/T oil (other than the OEM recommendation), 75W-140NS would be the oil of choice.
I'm not recommending this practice but simply commenting on possible alternatives for others to consider.
Happy Motoring!
On a recent msprotege Forum thread, the question was raised as to whether SOME transmission failures in highly modified engines (especially those that see frequent drag, track or rally racing) might be due to inadequate lubrication rather than to a strength of materials issue. This being a possibility, the suggestion was made that a switch to a heavier viscosity oil might be beneficial in terms of increasing transmission life and reliability. This might be something that those of you with turbo or otherwise heavily modded n.a. engines might want to consider. The question then becomes, what would be an appropriate oil?
All of the following information comes from the Red Line oil website because the company has the most informative, comprehensive and complete array of technical specifications, data and descriptive information of any oil company website I know of.
Red Line makes three classes of oils suitable for M/T cars: Synthetic M/T Lubricant, Synthetic Gear Oil and ShockProof Gear Oil. The synthetic M/T lubricant, MT-90, is considered the oil of choice for our Protege transmissions.
The ShockProof oils (SuperLight, Lightweight and Heavy ShockProof) are not recommended for synchro type transmissions as Red Line considers these oils too slippery for optimal synchro engagement. Consequently, although LightWeight is a 75W-140 rated oil and Heavy is rated at 75W-250, neither oil is suitable as a higher viscosity replacement because of the synchro problem.
In the Gear Oil category, both the 75W-90 and 80W-140 are also not recommended by Red Line for the same reason-both oils are too slippery and thus prevent rapid synchronization. The two Gear Oils Red Line DOES recommend for M/Ts with synchros are 75W-90NS and 75W-140NS (both GL-5 rated oils) because, according to Red Line, "these gear oils don't contain the friction modifiers for limited-slip hypoid differentials. This makes the transmission synchronizers come to equal speeds more quickly, allowing faster shifting and much easier low-temperature shifting." Further proof of the suitability of these oils for our transmissions rests on the fact that these two oils are also listed in the M/T lubricant category along with MTL and MT-90. Clearly, it would seem that for those who think they may need a heavier viscosity M/T oil (other than the OEM recommendation), 75W-140NS would be the oil of choice.
I'm not recommending this practice but simply commenting on possible alternatives for others to consider.
Happy Motoring!
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