Massive MPG hit of -10 mpg

romad

Top Post Dawg
Joined
May 27, 2011
Location
Prescott, AZ
TDI
2005 Jetta GLS Wagon "Cranberry"
I don't know if it is due to my new elevation here in Prescott, AZ or to the non-CARB Diesel I now have to use.
 

Andyinchville1

Veteran Member
Joined
Apr 7, 2016
Location
Virginia
TDI
2003 Jetta TDI wagon, 5 sp, 226K miles
Hi

I have heard of number 1 and number 2 diesel , bio Diesel , red diesel, black diesel, off road diesel, premium diesel and even some sort of diesel with water emulsion in it but what is CARB Diesel? (sounds like good stuff if regular diesel lops off 10 MPG (of course elevation could be it too in part etc..).

Thanks

Andrew
 

hskrdu

Top Post Dawg
Joined
Oct 17, 2003
Location
Maryland and New England
TDI
2003 Golf GLS 4D 5M, 2015 GSW SE 6M
Diesel in CA must meet the California Air Resources Board specs, which differs from many other states. There also seems to be more high cetane diesel available in CA, which can offer higher FE for many owners.
 

Andyinchville1

Veteran Member
Joined
Apr 7, 2016
Location
Virginia
TDI
2003 Jetta TDI wagon, 5 sp, 226K miles
HI,

FWIW , the other day (well 2 days in a row actually) I bought diesel from a gas station that advertised using 47 Cetane Diesel fuel .... This was up from my typical 40 Cetane Diesel fuel (or 40 Cetane fuel with up to 5% bi diesel at Cost Co).

Anyways, My MPG did not make noticeable changes (I'll post them in my fuelly later when I get time).

So unless , the extra 3 points of Cetane makes a big difference, my guess the OP lost 10 MPG mainly from other reasons (since I did not gain significant MPG when going to a higher cetane value (I did add 1 OZ of Power Service gray bottle / 1 OZ TC3 2 stroke per gallon also) BUT there may be other things in CARB diesel beyond extra Cetane that could help MPGs?

Andrew
 

CantWrite

New member
Joined
Jun 8, 2021
Location
Placerville CO
TDI
2003 Jetta Wagon (ALH/5-spd), 2005 Passat Wagon (BHW/5-spd conv)
I live at 7500' elevation, routinely drive over 9000' on my 100-mile round trip commute, and often over 10k'.

I use opti-lube summer and winter in their respective seasons to their minimum dosage. I tried doubling the dose only waste money. I notice a 1.5-2 mpg gain using the additives.

I put 70K on a 2002 NB, S7, PP520's, and perfectly timed/modified by Anut at Dieselland. (347K when I sold it) It routinely returned 48 mpg winter and 52 mpg summer. This is driving without concern for mileage, passing when I wanted, using the AC, etc.

I put 50K on a 2003 Jetta Wagon, completely stock with 277K on original clutch, injectors, etc. Routinely returned 48 mpg summer and 45 winter with skybox mounted on top in the winter to hold skis. Again, driving without care for mpg. I timed this one which could be the problem.

I am "from" South Dakota, and when I drove those cars back there (~1300' elev.) I did not notice a jump in mpg at all. What I did notice is that my glow-plugs would only cycle just a few seconds even on a cold engine and the thing would fire right up. Much longer glow up here in CO.

I buy my diesel at City Market/King Soopers, as I like the $1.00/gallon savings on 35 gallons and we all have to eat! I read about it, but cannot remember their cetane rating, but I believe they just get the leftovers of the local supplier without a proprietary blend of additives.

Sorry for your huge hit in MPG. I do not think elevation is to blame, although I am one of the more dull knives.
 
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