Sending unit question
 

Is there a difference in sending units between a 16 gal and a 20 gal tank?

Re: Sending unit question
 

I've been looking for one for my 77 dualie and what I am seeing on Rock auto is 2 outlet or 3 outlet drivers side or passenger side.

If you click on the part number in blue it shows what it fits but doesn't distinguish between 16 and 20 gallon tanks https://www.rockauto.com/en/catalog/...ding+unit,4436

Checking the height and width where the sender sits they are the same on both tanks. Some sites say that the 16 gallon is a short box tank looking at the photos it looks like the added capacity is at the front of the tanks.

Re: Sending unit question
 

They are the same for both size tanks. They differ on whether right or left side and 2 or 3 tube. I can't remember what year they went from 2 tube to 3 tube on the fillers, but I believe it was around 1978.

Re: Sending unit question
 

The third tube is your return line. If you have a return line from the fuel pump you need all three.
Not sure exactly when the return line became standard equipment but I believe it was available in the early 70's...

I don't believe you can install 20 gallon tanks with a 6' box.

16 & 20 gallon pickup tanks are the same depth so they use the same supports and the same senders. Blazer and Suburban tanks have differing depths.

The senders are side specific but the supports are not.