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Old March 5th, 2011, 19:17   #1
bfrinkus
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Join Date: Oct 2010
Location: Watkinsville, GA
Default mods and effect on mpg

I LOVE these forums, but have a beef with relative lack of data relating mods to fuel economy. I see a lot of "I did x and got about 10% mpg improvement!". Many claims are unrealistic and don't take into account all possible variables. Here's my approach to make a contribution to these forums:

-all mods are performed by me, but primary driver of the car (1997 jetta tdi sedan 5 spd manual) is my wife. She is not aware of what mods are made or when so this should eliminate placebo effect.
-all "fillups" are comprised of fuel ups of at least 8 gallons.
-all mpgs reported are 3 tank averages directly before/after mod. This should eliminate a one tank outlier where maybe the fuel tank doesn't get filled all the way to the top.
-all fuel ups are as consistent as possible in method.
-my wife's driving routine and habits are pretty dang consistent. She's no hypermiler, but consistently upshifts at 2000 rpm and drives at or 5 over the speed limit.
-I perform 1 mod at a time so as not to confuse results.
-car was purchased used with "high" miles of 216k. Car was dealer maintained and 100% unmodified when purchased.

EGR kit by dieselgeek:
-mpg before 44.9
-mpg after 44.3
-conclusion, not a smart mod if for mpg. However, this is a well made kit that serves an important purpose. I recommend this kit.

Switch from conventional motor oil to synthetic oil:
-mpg before 44.3
-mpg after 44.1
-again, if for mpg only, you're out of luck. There is lots of discussion on here about this topic. I think synthetic is great, read some other posts and see what you think.

Fuel quality: some companies clearly disclose diesel cetane, other companies won't let the cat out of the bag. I switched from bp (company publicly claims to sell diesel with cetane of 40) to QT (neither corporate nor stations can/will tell me what cetane they sell).
-mpg before (bp): 44.1
-mpg after (QT): 46.1
-WOW! I actually set 2 tank mpg records in this 3 tank span. This reinforces the importance of fuel quality on performance of our diesel engines. Again, there are some great posts telling what fuels are what quality. Take the time to find the best fuel in your area...as my experience shows, it may be worth a few miles a gallon!

I recently added MotorKote hyper lubricant to my engine. My gut tells me it's snake oil, but there's only 1 way to find out, huh? If there's anything ya'll want me to try, let me know! If it's cheap and not dangerous in my opinion, I'll do it. If it's expensive and you're willing to foot the bill, I'll do it.

More to come soon...

Best,
Brad
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