Diesel Place banner
1 - 4 of 4 Posts

·
Registered
Joined
·
179 Posts
Discussion Starter · #1 ·
I just got my 2022 GMC 3500 cab & chassis from the upfitter. It was ordered with the dual fuel tank option. In reading the diesel supplement manual page 29 says "refuel the primary front tank first, then add fuel to the auxiliary rear tank." According to the upfiter the front tank is the "extra" one because that's where they normally relocate the DEF tank on trucks with only one fuel tank. Since I had dual tanks they had to cut a piece out of the service body to get it to fit around the DEF tank since they couldn't move it.
On page 406 of the main owners' manual it lists the tank sizes as being 23.5 gallons front, 40 gallons rear. It sure seems like the primary tank would be the larger 40 gallon rear tank.
So, do I fill the rear first or the front first? The real question is why in the world would it matter which tank gets filled first?
Along that line, say I only want to put a few gallons in and not fill the truck, does it matter which tank I put it in? Should I split the fill, no matter how small between tanks?

This is probably overthinking but I generally like to go by what the manual says on any vehicle. This one seems contradictory.

Thanks for your help.
Wheel Tire Car Vehicle Automotive parking light
 

·
Registered
Joined
·
3,144 Posts
Don't know it this helps, but it is additional information.

(My interpretation is that on trucks with both tanks, the front 23.5 gal the primary one.
The only time the rear 40 gal one is primary is if it is ordered with the rear only.)


2022 Fuel tank options for the Cab&Chassis trucks, as listed in the Fleet Order Guide.

Standard:
N2N Fuel tank, front and rear, 63.5 gallon

Optional:
N2M Fuel tank, front only, 23.5 gallon

Optional
N2L Fuel tank, rear only, 40 gallon, mounted between frame side rails and behind rear axle
The N2L option - Requires (L5P) Duramax 6.6L Turbo-Diesel V8 engine. Required for DEF tank relocation to inside the frame rails - includes DEF tank relocation mounting kit.



The upfitter docs include instructions for relocating the def tank if an upfitter needs to do so.

The upfitter docs also have instructions for removal of the front (primary tank (if an upfitter needs to do that so they a relocate the def tank.
https://www.gmupfitter.com/wp-content/uploads/2021/07/UI-Bulletin_-171b.pdf

If you have both tanks fill the front 23.5 gal first.
The recommendation must have something to do with the rear tank pumping to the front.
 
  • Like
Reactions: OkDually

·
Registered
Joined
·
179 Posts
Discussion Starter · #3 ·
So I filled the truck for the first time today. The gauge was reading about 1/3. The front tank only took about 4 gallons. The rear tank took about 39. That leads me to conclude that it drains the rear tank first and then the front. I would have thought it would use them both at the same time.
 

·
Registered
Joined
·
3,144 Posts
1 - 4 of 4 Posts
Top