But you need to look each time.
Of course, at Load One, a 15 gallon purchase gets you a full shower credit, and along with the 6 cent per gallon discount, makes going even a mile or two out of your way for 20 , 30 or even 50 cents uneconomical (if all you want to do is put in 15 gallons to get the shower credit).
People need to also keep in mind the quality of fuel they are getting at other places.
Yeah, generally speaking, people with TDI vehicles, Sprinters especially, should be using as close to 50 cetane fuel as possible. If you can't find it (or are unsure), then using a cetane improver (Power Service, Standyne) is wise.
Fuels with lower cetane number have longer ignition delays, providing more time for the fuel combustion process to be completed. Thus, higher speed diesel engines (that's us) operate more effectively with higher cetane number fuels.
Sprinter engines will run on 40 or higher cetane (generally, 40-42 is the minimum range we find out there), but they are designed specifically for Eurodiesel, which is (now) minimum 51 cetane. I have been told that the Ford Transit and RAM Promaster engines are also designed for 51 cetane, but I have not been able to confirm that from any kind of official source, other than the the laws in most of Europe state that engines must be designed for the EN 590 fuel specs, which is 51 cetane. So, maybe. The overwhelming majority of Canadian diesel is 50 cetane minimum, as is California's CARB diesel (now 53). A few states have started mandating 48 and up cetane, like
Texas with their 110 county (PDF map) TxLED program. It's basically the eastern third of the state, east of I-35.
Most diesel at the pumps come from the same rack from the refinery or distributor, regardless of the brand. A few branded fuels, either because they have their own refineries or because they add a cetane improver (usually pure 2-ethylhexyl nitrate or di-tert-butyl peroxide) at the piped source or in the tank of the delivery truck will guarantee their diesel fuels.
This list is from the TDI Forums, where they keep track of it and update it as necessary. They are really anal about it, in part because a fe Volkswagen engines require a minimum of 50 cetane to prevent voiding the warranty. Also, the lubricity of diesel sold in the US is below that of Volkswagen's requirements.
Propel HPR, 75
Syndiesel, 60
BP (Amoco branded), 51;
Countrymark fuels Diesel-R, 50
Chevron, 49; or 51 with Techron D labels in select markets
ConocoPhillips through the 76 stations (California) 47-53
PetroCanada, 47-51
BP (Powerblend 47, otherwise 40-42)
Shell, 46;
Sinclair, 46;
Sunoco Gold, 45 (often +1-5) Sunoco regular is usually 40.
Exxon/Mobile, 43-46
Holiday Stations, 40-43
HESS, 40-42, can be up to 45.
Husky, 40 + diesel Max additives raise another 1-3 from there (41-45 max)
QuikTrip, 40 + lubricity additive
Pilot/Love's/Flying J/Valero/Sheetz/Walmart/Wawa: 40
B100 is 55 cetane, and B20 is 50 cetane, but will clog the injectors, fuel lines, and break down the seals in most Mercedes engines, so if you're using B20 or higher, you need to use a good dose of Howes Meaner Cleaner along with it.
Diesel that is marked "Premium" at the pump is usually 50 or higher cetane, often between 55-60. "Premium" means additives have been used to improve flow, detergents to clean the injectors, and water dispersants (basically, like adding Power Service or something), and almost always usually comes a cetane booster.
There are some QuikTrips in Missouri and Oklahoma (especially around KC) where they have truck diesel islands, and most of those are 48-52 cetane.
I stick to the BP Amoco and Powerblend, Chevron, ConocoPhilips (which is some Flying J's), and Shell when I can. Otherwise I get what I can and use Power Service (white bottle in winter, gray in summer). Most TA's use BP branded fuel.
Of course, there are some people (even those with Sprinters) who have never used a diesel fuel additive and have gone hundreds of thousands of miles without problems. YMMV.