when using a full flow oil filter on a 261 do you need to use more oil ?
Presumably you are referring to the GM full-flow oil filter assembly (58-63)?
Use of any oil filter will require more oil than is needed without any filter.
The 1959 GM full-flow oil filter does not drain out much when the engine is off (the inflow and outflow are both in the cap/cover).
The 1959 Truck Owner's Manual says the engine has a 5 qt capacity and the Jobmaster (261) oil filter holds 2 qts. Most likely the capacity is approximately 5qt+2qt=7qt.
I'd put in 6 qts at the next oil
&filter change; then, run the engine;, then, stop the engine. After about 3-5 minutes, check the oil level. Add oil as needed, and then repeat from "run the engine;".
