We have a GMC 2500 with a stock 36 gallon fuel tank. As we are planning a cross-county trip soon, what are thoughts/opinions on installing an auxiliary tank. Does anyone have experience with the kind you install in the bed of the truck? Any comments would be helpful. We pull a 27' fifth wheel. Thanks!

RDS makes a series of aux tanks and some with toolboxes. I have a 40 gallon in my truck. With your 3/4 ton truck you need to be sure your GVWR and rear axle GAWR are sufficient to carry the added fuel plus the trailer pin weight,Ken

Why? 300 miles between stops is doable anyplace in the US

I had similar concerns years ago with my 06 Duramax and it's 26 gal tank. I really, really wanted an extra diesel tank. Finally decided to just carry a 5 gal jerry can and a siphon hose in case I really got in trouble. We need the bathroom breaks every couple of hours anyway, and I decided for me it was just another toy (I like toys).I'd rather have the tool box room instead of surrendering it to an extra diesel tank. Also a little worried about ending up upside down some day with diesel dripping down my neck and something nearby sparking.

I agree with donn0128 above:This is America. There is a McDonalds, a Starbucks, a Subway, and a fuel station at almost every off ramp and most intersections where ever you will go on your cross country adventure.Follow the 1/4 till empty rule and you will be fine.have a good trip.

Sister in law kept good track by using gas buddy and planning where to fuel. She says they have almost it paid for after 6 years. She also mentioned the biggest savings is planning what state to fuel up in if given a choice. Such as AZ and Calif. They fill up close to state lines where next state over has higher taxes. She started keeping track because her husband said it would pay for itself shortly. He has it set up without any pump. He gravity feeds it thru a hose from extra tank in pick up bed to regular fuel tank. She hasn't figured in cost of hauling it around according to her. She has her numbers down to the decimal and reminds her husband often how quickly or more accurate, how long it has taken to break even. Or as she puts it, almost back to zero.Personally I would like one, just because of a couple times having to fuel at places that are taking advantage of their location. Such as Death Valley CA. I think all the station owners are related to each other at that lovely place.

auxiliary fuel tank for diesel truck | Good Sam Community

32 Replies

GoPackGo
Explorer
Sep 22, 2015
RDS gravity flow systems don't overflow. There is an in-line check valve that detects fuel backing up and closes, stopping the flow.

Is it possible that the thing could malfunction - I suppose. Has mine - no. If it ever does, I would just get a replacement.

Simple is good.
bmet2000
Explorer
Sep 22, 2015
Love my 98 gallon transfer flow in bed tank. Gives me 1000+ of towing miles to find the cheapest fuel.
Who uses gas buddy to find the cheapest fuel for hundreds of miles away? This guy does...
I wouldn't drive 100 miles out of the way, but I can always find the cheapest on my route.
Mine has the pump built in, so I don't have to turn anything on or off. Some gravity feed systems can overflow if you forget to close a valve or switch. Sure they are cheaper, but my brain doesn't always remember things... (Don't talk to me when I am using my black tank rinser and have the valves closed...)
Grit_dog
Navigator II
Sep 22, 2015
glodeke wrote:
We have a GMC 2500 with a stock 36 gallon fuel tank. As we are planning a cross-county trip soon, what are thoughts/opinions on installing an auxiliary tank. Does anyone have experience with the kind you install in the bed of the truck? Any comments would be helpful. We pull a 27' fifth wheel. Thanks!

Hey check out my add on Seattle craigslist for a JME tank I have for sale. 38-39 gal, compact baffled diamond plate. Or call me 970-319-0630. May be what your looking for, for cheap. And close to home! I'm in King Co.
TexasRangerRzR
Explorer
Sep 21, 2015
azdryheat wrote:
I installed a 91 gallon tank/tool box by RDX and love it. What I don't miss is finding fuel mid-day and then having to drag a 41' trailer through the station. I can go a couple of days between fill-ups and then fill up at my leisure minus the trailer. Such a relief.

This is why I have the same set-up. Buy fuel when it is convenient, and/or cheap.
RBPerry
Explorer
Sep 21, 2015
With gas most have the fuel pump in the tank. the fuel is also returned to the tank via a return line. So when installing two tanks in a gas vehicle you don't use a crossover. You would install a fuel pump in and return line in the new extra tank, or at least I would. This would be a lot of work though.

You could use a crossover or transfer between the two if you wanted to, and that would be the easiest way.
patperry2766
Explorer II
Sep 20, 2015
Is there a reason that transfer tanks are diesel only is because it is considered nonflammable as opposed to gasoline which is flammable?
ktmrfs
Explorer II
Sep 16, 2015
The 26 gallon on my 04 was a royal PITA even with the diesel. To many times I'd have to stop after 100 miles in order to make the next stop out in the middle of the puckerbrush. Finally started carrying two 5 gallon cans, which was fine.

On our 2015, thankfully it has the 36 gallon tank and based on my previous 10 years of towing, I think will be adequate. Yes, a 50+ gallon tank filled at a low cost station, or being able to go several days would be nice.

If I had planned on keeping the 04 a few more years I'd have gone with a 50 gallon replacement tank to keep the bed empty.

FWIW the longest trip I've done with the 2015 (running empty of course) was 750 miles without filling, and I still had 5 gallons in the tank when I filled. Just shy of 25mpg, and that included going over the continental divide and two passes in Idaho. Course to do that DW was driving the duramax following me driving a 26ft uhaul at 60mph ish the whole way.
RBPerry
Explorer
Sep 16, 2015
Many trucks have enough room for an additional tank between the body and frame rails. The problem with this is installing the fill piping and cap assembly. I have done two for customers and they came out very nice. We used crossover hoses so the tanks would remain balanced, Same amount of fuel in each tank). This does require cutting the access hole in the body, we matched it to the original. Most of the cost was in the body work and paint.

The thing is, it isn't necessary to keep the tanks full when not needed for long traveling. I think this option is much safer than a fuel tank in the bed of the truck, and it doesn't take up any bed space.
BarryG20
Explorer
Sep 11, 2015
You might try looking at Transfer flow fuel tanks and titan fuel tanks. They both make midship replacement tanks that replace the existing fuel tank with a larger one.
https://www.transferflow.com/fuel-tanks/replacement-tanks
https://titanfueltanks.com/product-category/mid-ship-fuel-tanks/
pennysmom09
Explorer
Sep 11, 2015
Lynnmor wrote:
Replaced my silly 26 gal. tank with a 50 gal. Best thing I did to the truck. Now I get to choose where to fill and how much to pay. With a trailer in tow, not every station is an easy stop. And in Death Valley the suckers wanted over $5 a gallon and it was nice to drive on by.

X2. Love not having to fill up,with fiver in tow!