I am creating a two tank system, using the stock tank for WVO and a small for starting and purging. I live in LA where cold is not much of a problem. Is there any reason not to use the stock return and have both fuels return to the WVO tank. One less thing to switch, less to buy, less to break. Thanks

Unless its 180*f in LA, temperature is a problem.

Looping the return leaves no place for air to escape except through the injectors.

Routing the diesel return to the wvo tank will result in a lot of diesel in the wvo tank. It takes a few miles for the car to warm up enough to switch it over, in the mean time all that diesel is going into the wvo tank. Greasecar uses a looped circuit. Forced Induction is correct - air is REALLY hard to get out of the system. When everything is good, well, it's good. A small air leak will drive you nuts though - ask me how I know.

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Brad
1981 300TD - daily driver
1963 Chevy II
2001 F-250 7.3 Power Stroke

In addition to the air, polymerization will occur if using the stock tank for WVO, resulting in chronic clogging. The two fuel systems need to be kept scrupulously separate. You would be better served with a more typical 2-tank setup using a heavy plastic or aluminum tank for WVO and keep the stock tank stock.

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1983 CD
1958 Studebaker Packard (being resuscitated)

With both WVO and Diesel returned to the Diesel tank you probably won't even be able to warm up the engine one time before you empty the startup/purge tank into the WVO tank.

You need to switch both the supply and return independantly to get a quick purge.

I actually use 3 solenoids for quickest switchover times, quickest purge times and effective air elimination.

Diesel returns to the diesel tank.
WVO is looped during WVO running.
WVO (and air) is returned directly to the WVO tank during Purge.

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Ron Schroeder
'85 300 Turbo Diesel 2 tank WVO
'83 300 Turbo Diesel 2 tank WVO
Some former WVO vehicles since ~1980:
'83 Mercedes 240D
'80 Audi 4000D
'83 ISUZU Pup
'70 SAAB 99 with Kubota diesel
'76 Honda Civic with Kubota diesel
'86 Golf
Several diesel generators
All with 2 tank WVO conversion
LI NY

I missed that one! Steel tanks and straight veg don't mix. My filler cap on my truck tank needs to be cleaned periodically because of the polymerization.

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Brad
1981 300TD - daily driver
1963 Chevy II
2001 F-250 7.3 Power Stroke

how about treating or sealing the stock tank with one of those liquid tank sealers or "tank cream" products? slosh it around to coat the inside of the stock tank so there is no more exposed steel inside the tank.

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1987 300TDT
1981 VW MKI Caddy 1.6 diesel, waiting on engine swap
1983 D-50 Power Ram 4x4 "Mitsubishi" 2.3 turbo diesel
assorted gas powered crap and motorcycles

RIP: 1984 300TDT, 1982 300TDT, 1984 190D 2.2, 1992 300D 2.5, 1987 300TDT, 1982 Maxima LD28, 1983 Maxima LD28, Isuzu C223 P'ups X3, 1983 Holiday Rambler 6.2 Banks turbo diesel, 1984 Winnebago LeSharo 2.1 TD, 1985 Allegro 6.5