tank sending unit question - The 1947 - Present Chevrolet & GMC Truck Message Board Network

naphtali5725 · 06-08-2013, 07:42 AM

I have an 86 C10 with dual tanks. they both have three outlets on them.
I am buying new tanks, and want to get new sending units too.
I want to run a holley or other electric fuel pump with a regulator.
I plan on keeping the original dual tank tank switch valve, and switch on the dash.

Should I get tank sending units with just 2 outlets? or do I get the ones with 3 outlets?

I'm a bit confused on this one, since I have looked at a few holley electric pumps, and I don't see return lines on them, unless I'm looking at the wrong ones.

any suggestions? thanks guys

wraprail · 06-08-2013, 08:07 AM

I too have an 86 (or is it an 85?) don't matter in this case. Mine also has dual tanks with the factory switching setup.
I am using a high preformance machanical fuel pump and just plugged the 1/4" return line.
No problems.
If you are replacing the senders anyway then why not get the 2 hose senders.
That is what I would do.
That way you could remove that whole line. Maybe plug it at the switch valve.

I would like to know what that 3rd line is suposed to do if anyone knows.
I would guess to help Prevent vapor lock maybe?

SkinnyG · 06-08-2013, 10:49 AM

I just bought a new sender for mine, and I ordered a 3-outlet one just so that I could HAVE a return line should I convert to fuel injection at a later date. Just cap the 3rd outlet in the mean time.

naphtali5725 · 06-08-2013, 11:15 AM

For a 2 outlet, I thought one went to the fuel pump to feed it, then one was the return,
On a 3 outlet I have no idea what the 3rd one is for... I guess that's basically my real question... is the 3rd outlet for some emissions control stuff?

wraprail · 06-08-2013, 11:23 AM

Third outlet (5/16 line that does not connect to the switching valve) goes to the charcoal canister.

naphtali5725 · 06-08-2013, 11:25 AM

Quote:

Originally Posted by wraprail

Third outlet (5/16 line that does not connect to the switching valve) goes to the charcoal canister.

then I guess I can just get the 2 outlet type... I don't have a charcoal canister... or should I get one?

wraprail · 06-08-2013, 11:32 AM

Depends on how strict your home state is on emission testing and if you ever plan to move to a state that is serious. Like say California or Nevada maybe.

The canister should be mounted in a round bracket located on the driver side of the core support right next to the radiator.

**rs74** · 06-08-2013, 09:26 PM

Isn't the third line just a vent line?

**hatzie** · 06-09-2013, 10:02 AM

I think all senders have a vent line...
3 line senders were (not in any order) vent, feed, and return and 2 line senders were vent and feed with no return.

naphtali5725 · 06-09-2013, 10:59 AM

Quote:

Originally Posted by hatzie

I think all senders have a vent line...
3 line senders were (not in any order) vent, feed, and return and 2 line senders were vent and feed with no return.

thanks hatzie!

Tucson38 · 06-11-2013, 10:15 AM

I was under the impression that the third line was fuel return to prevent vapor lock. But I'm no expert.

dieseldawg142 · 06-11-2013, 07:29 PM

when i went to f.i. i replaced my senders with the 3 outlet senders. like hatzie says, feed, return, & vent

06-08-2013, 07:42 AM	#1
naphtali5725 Registered User Join Date: Mar 2012 Location: NC Posts: 1,101	tank sending unit question I have an 86 C10 with dual tanks. they both have three outlets on them. I am buying new tanks, and want to get new sending units too. I want to run a holley or other electric fuel pump with a regulator. I plan on keeping the original dual tank tank switch valve, and switch on the dash. Should I get tank sending units with just 2 outlets? or do I get the ones with 3 outlets? I'm a bit confused on this one, since I have looked at a few holley electric pumps, and I don't see return lines on them, unless I'm looking at the wrong ones. any suggestions? thanks guys __________________ My build thread... http://67-72chevytrucks.com/vboard/s...d.php?t=515829 Disabled Veteran 82nd Airborne Division Operations: Desert Shield, Desert Storm, and Uphold Democracy

06-08-2013, 08:07 AM	#2
wraprail Registered User Join Date: Sep 2010 Location: Lake Havasu City Arizona Posts: 863	Re: tank sending unit question I too have an 86 (or is it an 85?) don't matter in this case. Mine also has dual tanks with the factory switching setup. I am using a high preformance machanical fuel pump and just plugged the 1/4" return line. No problems. If you are replacing the senders anyway then why not get the 2 hose senders. That is what I would do. That way you could remove that whole line. Maybe plug it at the switch valve. I would like to know what that 3rd line is suposed to do if anyone knows. I would guess to help Prevent vapor lock maybe? __________________

06-08-2013, 10:49 AM	#3
SkinnyG Registered User Join Date: Feb 2012 Location: Beautiful BC, Canada, eh?! Posts: 2,265	Re: tank sending unit question I just bought a new sender for mine, and I ordered a 3-outlet one just so that I could HAVE a return line should I convert to fuel injection at a later date. Just cap the 3rd outlet in the mean time. __________________ 1961 Apache: "Grabber Orange" Shortboxed, pancake, step-notch, air-ride, turbo, LS 1977 Silverado: Shortboxed & dropped, potato-potato V8 Pontiac Firefly (Chevy Sprint): The ultimate engine swap: 5.7L in a 1.0L bag Lotus Super 7 Replica: Scratch-built street-legal rollerskate

06-08-2013, 11:15 AM	#4
naphtali5725 Registered User Join Date: Mar 2012 Location: NC Posts: 1,101	Re: tank sending unit question For a 2 outlet, I thought one went to the fuel pump to feed it, then one was the return, On a 3 outlet I have no idea what the 3rd one is for... I guess that's basically my real question... is the 3rd outlet for some emissions control stuff? __________________ My build thread... http://67-72chevytrucks.com/vboard/s...d.php?t=515829 Disabled Veteran 82nd Airborne Division Operations: Desert Shield, Desert Storm, and Uphold Democracy

06-08-2013, 11:23 AM	#5
wraprail Registered User Join Date: Sep 2010 Location: Lake Havasu City Arizona Posts: 863	Re: tank sending unit question Third outlet (5/16 line that does not connect to the switching valve) goes to the charcoal canister. __________________

06-08-2013, 11:32 AM	#7
wraprail Registered User Join Date: Sep 2010 Location: Lake Havasu City Arizona Posts: 863	Re: tank sending unit question Depends on how strict your home state is on emission testing and if you ever plan to move to a state that is serious. Like say California or Nevada maybe. The canister should be mounted in a round bracket located on the driver side of the core support right next to the radiator. __________________

06-08-2013, 09:26 PM	#8
rs74 Senior Member Join Date: Jun 2010 Location: Illinois Posts: 2,957	Re: tank sending unit question Isn't the third line just a vent line? __________________ Roy 85 Short Bed Silverado- Work in progress. http://67-72chevytrucks.com/vboard/s...d.php?t=564818 1987 R10 shortie

06-09-2013, 10:02 AM	#9
hatzie Moderator Join Date: Oct 2008 Location: Wentworth, NH Posts: 4,977	Re: tank sending unit question I think all senders have a vent line... 3 line senders were (not in any order) vent, feed, and return and 2 line senders were vent and feed with no return. __________________ 1959 M35A2 LDT465-1D SOLD 1967 Dodge W200 B383, NP420/NP201 SOLD 1969 Dodge Polara 500 B383, A833 SOLD 1972 Ford F250 FE390, NP435/NP205 SOLD 1976 Chevy K20, 6.5L, NV4500/NP208 SOLD 1986 M1008 CUCV SOLD 2000 GMC C2500, TD6.5L, NV4500 2005 Chevy Silverado LS 2500HD 6.0L 4L80E/NP263 2009 Impala SS LS4 V8 RTFM... GM Parts Books, GM Schematics, GM service manuals, and GM training materials... 1973-1991 GM Light Truck Service, Unit/Overhaul, Wiring Manuals, Parts Books and Some 1968-1999 GM Service Training textbooks in PDF 1988-1998 GMT400 CK service manual project 1988-1993 GMT400 CK parts books. 1967-1972 GM Light, Medium, & Heavy Truck Service Manuals in PDF Please include at least the year and model in your threads. It'll be easier to answer your questions. And please let us know if and how your repairs were successful.

06-11-2013, 10:15 AM	#11
Tucson38 Registered User Join Date: Aug 2011 Location: Tucson Arizona Posts: 164	Re: tank sending unit question I was under the impression that the third line was fuel return to prevent vapor lock. But I'm no expert.

06-11-2013, 07:29 PM	#12
dieseldawg142 Registered User Join Date: Jul 2011 Location: back 40, bc Posts: 3,903	Re: tank sending unit question when i went to f.i. i replaced my senders with the 3 outlet senders. like hatzie says, feed, return, & vent



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