I have a 1966 Cutlass Sports Coupe with a 330ci, factory four barrel Rochester, AC & Automatic. I just received my new Ni-Terne steel fuel tank and sending unit. I ordered them with a 5/16" fittings because I thought I read that was correct. Was I correct in what I ordered? I hope so, the thought of shipping that back hurts my wallet. Thanks for your input.

 

Should be 3/8 with no return line. I believe GM used 3/8 lines on cars with Q-Jets. 442's used a 1/4 return line. Did you order the 66 tank or a 67 that they say fits a 66? The vent line system on a 66 is different from a 67.

 

My replacement tank came from OPGI. It's listed for a 66-67 Cutlass, 1 vent, 20 gallon. I will borrow a mic from work and speck out the sending unit and vent nipples. I have the body off of the frame and the gas tank out, so I can do a quick comparison with the new tank and my original. I will double check the vent location too and post my findings tomorrow.

 

If it has 2 vents in the rear of the tank it's a 67 style and if it has one vent in the right front upper it's a 66 style. This has been an issue for a very long time with vendors selling/listing the 67 tank as a 66 and that's wrong.

 

It definitely has one vent.

 

My 66 cutlass holiday coupe 330ci, four barrel carb had a single 5/16 fuel line with a single vent fuel tank.As stated the fuel tank should have one vent, front upper right.

 

That's interesting on the 5/16 supply line. Only built 442's and they had the 3/8's lines. I stand corrected.

 

All is good with my gas tank and sending unit purchase from OPGI. My 66 Cutlass Sports Coupe got a new ni-terne steel, 20 gallon gas tank with the correct 5/16" fitting and vent location. As Nick stated it has one vent, no return line and 5/16" fittings. My factory Service Manual says that there were 3 gas tanks for the 66 Cutlass. One tank for the 330ci with no return line and one vent. This stayed the same with or without AC. The two other style gas tanks were for the 400ci engine. If AC was present, then a return line was in the mix. If AC was not present on the 400ci, it had no return line. All gas lines were 5/16" and the return line (if it had one) was 1/4". I appreciate everyone's input.

 

 

I'm not sure where in the service manual you got that info about the fuel lines/tank. First there was not any difference between a Cutlass & 442 fuel tank. The difference is the sending unit. All 66 442's had a 3/8 supply line and a 1/4return line A/C or not. Here is a picture of a very low mile 66 442 tri carb car that was parked in 1972 and is the most original unmolested car I've ever seen. Notice the non A/C with a return line.

 

This info I posted was from an original 1966 Oldsmobile Service Manual which is as big as a phonebook. My manual is not a reprint, but the real deal from back in the day. My manual only spoke of engine size (330 or 400) dictating what tank you got, not model. This weekend, I will try to take a screen shot of the page that describes the 3 gas tanks for 1966 and line sizes. I will post it if I can. Maybe the tri-carb setup was given bigger lines and my service manual did not mention it? That is an awesome picture that you posted! That 442 must have been a real screamer.

 

I have the same service manual you do. It's an original and not a reprint or copy. One thing to keep in mind is they print the service manuals way before the cars are built because they have to be @ the dealer before the cars. There is always engineering changes made throughout the production run. The PIM/assembly manual shows changes made and what date.Every 66/67 442 I've ever seen has the 3/8 supply and 1/4 return line no matter the options. Here's a picture of my 66 442 3x2 Sports Coupe.

 

You are so right! I appreciate everybody's comments, knowledge base and pictures.