.681 gear set. What kind of improvement?

[Oil_Burner]

.681 gear set. What kind of fuel improvement?

So, I just had the .681 fith gear set installed along with fresh Amsoil 75/90 synthetic gear oil. What kind of fuel improvement can I expect if I maintain my normal driving style? That is, I drive 60 on the highway. Prior to today I was averaging around 55-62 mpg depending on how much highway driving I did.


Thanks.

 

[SoCalC]

I've heard folks mention about 4% reduction if fuel use, depending on exactly how you're driving it. It's one of those mods I may never do, but am interested in.

It seems you may have overdone it on the gearbox oil viscosity, though sometimes sythetics seems to run thinner than conventionals for a given weight rating. I think something on the order of a 20wt ATF type fluid or lighter gear oil is more in line with what you ought to be running.

 

[TurbineWhine]

Your average fuel economy is very near the top of the curve that most people report for your year of TDI. Having said that, I'm not sure how much improvement you will see. When I did mine, I saw about 3 mpg improvement and my driving is about 75% highway. I typically will drive between 65 and 70mph on the interstate. I can drive aggressively and drop to 47mpg or I can drive ultra conservatively and get 56 mpg. So you see that driving style and hiway mix play a big role in the effects of the 5th gear mod. In my opinion the major benefit of the gear you have chosen is the RPM reduction at highway speeds. The noise level is down and the engine just sounds like it is working less to get me down the road.

By the way, the Bentley manual says that a SAE 75W90 mineral oil is OEM for your transmission fluid. Your choice of a Synthetic 75W90 should extend the life of your gear box. The oil you have chosen is the same oil I run in mine.

TW

 

[SoCalC]

By the way, the Bentley manual says that a SAE 75W90 mineral oil is OEM for your transmission fluid. Your choice of a Synthetic 75W90 should extend the life of your gear box. The oil you have chosen is the same oil I run in mine.TW

Wow, does this change anywhere to 03, or 04 and beyond? That viscosity seems a bit archaic for this type of application.