[PNW_i30]

My car has the 6-spd manual and I've noticed the 2nd gear synchro is a bit 'slow', especially when the engine is cold (first 10 or so miles of operation). Once fully warmed up it's better but not really where I'd like it to be as I still have to go a bit slower than 'normal' to keep the shifts smooth. I am not hard on my car and in fact very careful there. Shifting up/down through all the other gears are fine. Due to my work schedule the car has only has a few thousand miles on it now but I've not seen much of a change there since when I picked it up with 26 miles on the odometer.

Has anyone tried using a gearbox additive or a synthetic lubricant in their car? I've used Redline products to very good effect on a prior Toyota, Subaru and Nissan, all with 5-spd manual boxes. In each case the improvement in shift quality was very obvious and made the cars far more enjoyable to drive. That said, in my prior Hyundai, which was bought used and had a 5-spd manual, out of habit I also changed it over to the correct weight/type of Redline product but did not notice any difference - it in fact shifted and felt exactly the same as it had with the factory fill.

 

[Exeno]

My car has the 6-spd manual and I've noticed the 2nd gear synchro is a bit 'slow', especially when the engine is cold (first 10 or so miles of operation). Once fully warmed up it's better but not really where I'd like it to be as I still have to go a bit slower than 'normal' to keep the shifts smooth. I am not hard on my car and in fact very careful there. Shifting up/down through all the other gears are fine. Due to my work schedule the car has only has a few thousand miles on it now but I've not seen much of a change there since when I picked it up with 26 miles on the odometer.

Has anyone tried using a gearbox additive or a synthetic lubricant in their car? I've used Redline products to very good effect on a prior Toyota, Subaru and Nissan, all with 5-spd manual boxes. In each case the improvement in shift quality was very obvious and made the cars far more enjoyable to drive. That said, in my prior Hyundai, which was bought used and had a 5-spd manual, out of habit I also changed it over to the correct weight/type of Redline product but did not notice any difference - it in fact shifted and felt exactly the same as it had with the factory fill.

So long as the gear oil you're putting into the box has the appropriate GL rating, and meets or exceeds H/K's recommendation (API GL-4, SAE 70W TGO-9, according to the owner's manual, among other name-branded recommendations contained therein), it will not void the warranty and you should at minimum expect the same level of function and performance.

With any of my manual transmission vehicles in the past, I've used Redline's fluids. As well as their differential gear oil, for the couple of Subarus I had. They ended up operating more smoothly. Which was to be expected, as they were used vehicles, but gear oil is a fairly inexpensive fluid to "test" and see how much improvement there is in the gear action, if any.