If you don't know if it is thick becuase of the type of oil, or becuase it is contaminated, I would suggest you heat it and mist wash it. Then dry it well and see how it is. If it's still thick, it's probably just thick oil.

I wouldn't put it in my one tank without a fuel pump, and even then it would have to be pretty warm outside.

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1983 240D Silver/Blue "Sadie", unknown miles. 100k miles on WVO single tank, converted to 2 tank about 10k miles ago, FPHE, Injector Heaters, Aux Fuel pump. Alcohol/Water injection. Frantz oil bypass filter
1992 300D 2.5 Turbo Green/Tan "Jade" 267K miles Stock.
1992 300D 2.5 tan/tan "Rocky" on 2 tank WVO. Pressure actuated Turbo "rat's nest" surgery completed. 197k miles