Stovebolt.com Forums The Shop Area The HiPo Shop Under bed fuel tank options

I am trying to decide which fuel tank to pursue for my 1949/50 3600. I have seen several threads regarding using with a 1987 vintage Blazer 25 gallon tank or an early Mustang tank. I believe the Blazer tank is 28 3/4 x 28 1/8 x 10 3/4 and some have indicated that it hangs too low below the frame. I am not sure about the diemnsions of the Mustang tank.

My plan is to have the filler located in the fender rather than the bed. I have seen several threads regarding this arrangement and while it is more complex than coming up through the bed I think it is the approach I am going to take.

I am also hoping that the tank selection will still allow dual exhaust out the rear. I have seen at least one picture of a setup that had the exhaust going over the axle, then angled to be outside the frame to clear the tank, but I am not sure what tank was used.

I am planning to run a carburetor so no high pressure in-tank fuel pump, although a low pressure in tank pump might be desireable (otherwise an in-line electric pump).

If I understand correctly the 3600 rear frame may be slightly narrower than the 3100. I am planning to retain the original rear leaf spring suspension so I don't want to compromise the rear frame but I believe there is a simple angle cross piece that may have been for the spare tire that is not structual and could be removed.

You should start with your frame measurements. When you have that figured out you can use a site like US Tanks to find dementions. Check prices on other sites such as Rock Auto to get the best deal.

Apparently this is not going to be as easy as following someone else's example.

My frame cross section in the area behind the axle has a significantly wider lower flange (that is also tapered) than the upper flange. At the rear cross member the lower flanges are 29" apart, 29 3/4" apart at the cross angle location. Therefore the max tank width needs to be less than 29" to fit between the lower flanges.

The cross angle appears to be even with or slightly behind the rear differential. I believe the angle could be replaced/relocated forward slightly but as it sits the rear edge of the angle is 16 5/8" from the rear cross member. If it is relocated the existing front edge appears to be the furthest forward a tank could be and clear the differential rear cover. That dimension is more like 18 1/4" making the maximum fore/aft tank dimension approximately 18 1/4".

The Blazer tank measurements are okay for width (28 3/4") but the fore/aft dimension of 28 1/8" appears to be significnatly too long and would result in the tank overhanging the differential, possibly interferring as the suspension is loaded. The frame height is 4 1/4" so the 25 gallon Blazer tank at 10 3/4" high would hang 6 1/2" lower than the frame if mounted flush with the top of te frame.

Tanks Inc. shows a 1949-52 Chevy Fuel Tank 29-1/4" x 21-1/4" x 8-1/4" (16 Gallons) which seems too wide but may work depending on the overall width including a flange that would be either inside or below the frame channel. The length seems a little long but may be okay if the tank is moved as far back as possible with the rear flange either inside or below the rear cross member. https://www.tanksinc.com/index.cfm/...799/category_id=133/mode=prod/prd799.htm
the fuel filler location in the right rear coner looks good for a fender filler location but I am not sure how it will clear the frame rail unless the tank is mounted higher than the top of the frame (not sure about bed clearance). They also have an 18 gallon version that is 1" taller which may be okay if the top of the tank is above the frame rail for filler clearance.

Any insight from forum members would be apprecaited.

We will not use a tank that has the filler in the bed floor so use only side fill tanks. The early Blazer tanks have a shape that fits in the factory spare tire position and require zero frame trimming. A fill tube is run under bed floor out through the side and then up to a motorcycle pop up gas cap in the left rear fender. As the photos show the tank DOES NOT hang low and has dual exhaust with no clearance issues.

Note tank fits in factory spare tire area with no modification:
[img]https://i.postimg.cc/9R0xtNcv/003.jpg[/img] [postimg.cc]

No rust exhaust tube is run up to filler cap:
[img]https://i.postimg.cc/0rqnNQwT/004.jpg[/img] [postimg.cc]

If pop up cap is painted body color it's nearly invisible:
[img]https://i.postimg.cc/5X9k2tZ4/016.jpg[/img] [postimg.cc]

[img]https://i.postimg.cc/21vJtJRv/018.jpg[/img] [postimg.cc]

Coilover, your frame cross members appear to be significantly different than mine? Mine is a straight horizontal channel riveted inside of the top flange of the frame rail. Your frame rail seperation also appears to be wider than mine as the Blazer tank is reported to be 28 3/4" wide and my lower frame flange spacing is 29", it may be an optical illusion but your frmae rail flanges appear to have a lot more clearance than expected. Your tank is also clearly behind the rear differential but the Blazer tank is reported to be 28 1/8" long and my rear differential to rear cross brace is only approximately 18".

Thanks for the pictures and information regarding the side fill. It appears that the filler tube can be routed over the frame rail and have clearance to the bed which is good news.

The truck pictured is a 52 3100 so maybe 1/2T and 3/4T rails are different.

Coilover, thanks for the additional information. I will look at the frames in the factory assembly manual but I am guessing that the 3100 and the 3600 are different.

I measured one of my old bed mounting cross rails and it appears to be approx. 1 7/8" high so the filler pipe will need to be 1 3/4" max, probably more like 1 1/2" to have clearance to the bottom of the floor boards. The Tanks Inc 16 or 18 gallon tanks (noted above) have a 1 1/2" ID filler hose so that should be okay if I can get a short enough offset to get the pipe from below the frame top flange to above the top flange.

I reviewed the frame dimensions in the FAM and confirmed that the 3600 frame is significantly narrower than the 3100 frame. It seems for informaiton regarding tank options to be helpful it needs to be from a 3600 so that may be very limiting. I have requested additional information from Tanks Inc. regarding their tanks and hpe that they can provide some information such that I don't buy a tank only to find that it will not work.

I did not find any information in the FAM regarding the bed cross rail locations to determine where the filler can not be located and clear the cross rails. I did see at least one other tank installation that had a side fill that required a modification to the bed/side for the filler tube to come up through the floor and over the bed side angle strip. I am hoping that I will not need to take that approach as I would like the bed floor and sides to be straight/flat as originally designed.

That looks like a solid option for the 3100/3200s. When you say "early" blazer, approximately what year range are you talking about?

You got me on the year of the Blazer. I just take a tape measure to the junkyard for things like gas tanks and seats. I think the one pictured is from a 74 and do know they came in two capacities, 13.5g (?) and 20g.